Merge pull request #1468 from qelectrotech/resolve-1461

Speed up opening big projects with lazy folios

sources/TerminalStrip/terminalstrip.cpp

@@ -1011,6 +1011,15 @@ bool TerminalStrip::fromXml(QDomElement &xml_element)
 	auto xml_layout = xml_element.firstChildElement(QStringLiteral("layout"));
 	if (!xml_layout.isNull())
 	{
+			//The folios holding its terminals are built (QET_LAZY_FOLIOS):
+			//a strip is read with the project, before the database could
+			//tell where any symbol is
+		QSet<QUuid> terminals;
+		const QDomNodeList xml_reals = xml_layout.elementsByTagName(RealTerminal::xmlTagName());
+		for (int i = 0 ; i < xml_reals.size() ; ++i)
+			terminals.insert(QUuid(xml_reals.at(i).toElement().attribute(QStringLiteral("element_uuid"))));
+		m_project->buildFoliosHoldingSymbols(terminals);
+
 			//Get all free elements terminal of the project
 		const ElementProvider ep(m_project);
 		auto free_terminals = ep.freeTerminal();

sources/autoNum/autonumschemecommand.cpp

@@ -105,7 +105,9 @@ QList<Diagram *> AutoNumSchemeCommand::usersOf(const QETProject *project, Kind k
 	if (!project || title.isEmpty()) {
 		return users;
 	}
-	for (Diagram *diagram : project->diagrams()) {
+		//The schemes a folio uses are its own data, read on opening:
+		//folios() builds nothing
+	for (Diagram *diagram : project->folios()) {
 		if (kind == Kind::Conductor) {
 			if (diagram->conductorsAutonumName() == title) {
 				users << diagram;
@@ -234,7 +236,8 @@ void AutoNumSchemeCommand::rename(const QString &from, const QString &to)
 		if (m_project->conductorCurrentAutoNum() == from) {
 			m_project->setCurrentConductorAutoNum(to);
 		}
-		for (Diagram *d : m_project->diagrams()) {
+			//Folios' own data, read on opening: folios() builds nothing
+		for (Diagram *d : m_project->folios()) {
 				//The highest folio number given, kept by scheme title
 			for (auto *hash : {&d->m_cnd_unitfolio_max, &d->m_cnd_tenfolio_max, &d->m_cnd_hundredfolio_max}) {
 				if (hash->contains(from)) {

sources/autoNum/elementautonumschemecommand.cpp

@@ -369,10 +369,19 @@ ElementAutoNumSchemeCommand::NumberSupport ElementAutoNumSchemeCommand::numberSu
 std::optional<int> ElementAutoNumSchemeCommand::numberOf(const NumberSupport &support,
 														 const Element *element)
 {
-	if (!support.supported || !element) {
+	if (!element) {
+		return std::nullopt;
+	}
+	return numberOf(support, element->sequenceStruct());
+}
+
+/// @return the number the sequential numbers @p seq give, if the scheme knows it
+std::optional<int> ElementAutoNumSchemeCommand::numberOf(const NumberSupport &support,
+														 const autonum::sequentialNumbers &seq)
+{
+	if (!support.supported) {
 		return std::nullopt;
 	}
-	const autonum::sequentialNumbers seq = element->sequenceStruct();
 	const QStringList &list = support.type == QLatin1String("unit") ? seq.unit
 							: support.type == QLatin1String("ten") ? seq.ten
 							: seq.hundred;
@@ -385,14 +394,18 @@ std::optional<int> ElementAutoNumSchemeCommand::numberOf(const NumberSupport &su
 }
 
 namespace {
-/// The elements of @p project which follow the scheme @p title and are not slaves or reports
-QVector<Element *> numberedFollowers(const QETProject *project, const QString &title)
+/// The symbols of @p project which follow the scheme @p title and are not
+/// slaves or reports, built or not (QETProject::symbolNumbering())
+QList<QETProject::SymbolNumbering> numberedFollowers(const QETProject *project, const QString &title)
 {
-	QVector<Element *> list;
-	const auto followers = project->elementsUsingElementAutoNum(title);
-	for (Element *el : followers) {
-		if (el->linkType() != Element::Slave && !(el->linkType() & Element::AllReport)) {
-			list << el;
+	QList<QETProject::SymbolNumbering> list;
+	const QUuid id = project->elementAutoNumId(title);
+	if (id.isNull()) {
+		return list;
+	}
+	for (const auto &symbol : project->symbolNumbering()) {
+		if (symbol.numbered && !symbol.formula.isEmpty() && symbol.scheme == id) {
+			list << symbol;
 		}
 	}
 	return list;
@@ -411,13 +424,10 @@ QSet<QString> ElementAutoNumSchemeCommand::labelsHeldBesides(const QETProject *p
 	if (!project) {
 		return labels;
 	}
-	for (Diagram *d : project->diagrams()) {
-		for (QGraphicsItem *item : d->items()) {
-			if (auto *el = qgraphicsitem_cast<Element *>(item)) {
-				if (el != element) {
-					labels << el->elementInformations().value(QETInformation::ELMT_LABEL).toString();
-				}
-			}
+		//Folios not built yet answer from what building them would give
+	for (const auto &symbol : project->symbolNumbering()) {
+		if (symbol.element != element) {
+			labels << symbol.label;
 		}
 	}
 	labels.remove(QString());
@@ -453,8 +463,8 @@ std::optional<ElementAutoNumSchemeCommand::CounterConflict> ElementAutoNumScheme
 
 	CounterConflict conflict;
 	conflict.counter = counter;
-	for (const Element *el : numberedFollowers(project, title)) {
-		if (const auto number = numberOf(support, el)) {
+	for (const auto &symbol : numberedFollowers(project, title)) {
+		if (const auto number = numberOf(support, symbol.sequence)) {
 			if (*number >= counter) {
 				++conflict.count;
 				conflict.highest = std::max(conflict.highest, *number);
@@ -486,8 +496,8 @@ QList<ElementAutoNumSchemeCommand::GapRange> ElementAutoNumSchemeCommand::gapRan
 		return ranges;
 	}
 	QSet<int> used;
-	for (const Element *el : numberedFollowers(project, title)) {
-		if (const auto number = numberOf(support, el)) {
+	for (const auto &symbol : numberedFollowers(project, title)) {
+		if (const auto number = numberOf(support, symbol.sequence)) {
 			used << *number;
 		}
 	}
@@ -559,22 +569,19 @@ QList<int> ElementAutoNumSchemeCommand::freeNumbers(const QETProject *project,
 
 	QSet<int> used;
 	int highest = context.itemAt(support.partIndex).value(1).toInt();
-	for (const Element *el : numberedFollowers(project, title)) {
-		if (el == element) continue;
-		if (const auto number = numberOf(support, el)) {
+	for (const auto &symbol : numberedFollowers(project, title)) {
+		if (symbol.element == element) continue;
+		if (const auto number = numberOf(support, symbol.sequence)) {
 			used << *number;
 			highest = std::max(highest, *number);
 		}
 	}
 
 	QSet<QString> labels;
-	for (Diagram *d : project->diagrams()) {
-		for (QGraphicsItem *item : d->items()) {
-			if (auto *el = qgraphicsitem_cast<Element *>(item)) {
-				if (el != element) {
-					labels << el->elementInformations().value(QETInformation::ELMT_LABEL).toString();
-				}
-			}
+		//Folios not built yet answer from what building them would give
+	for (const auto &symbol : project->symbolNumbering()) {
+		if (symbol.element != element) {
+			labels << symbol.label;
 		}
 	}
 	labels.remove(QString());

sources/autoNum/elementautonumschemecommand.h

@@ -18,6 +18,7 @@
 #ifndef ELEMENTAUTONUMSCHEMECOMMAND_H
 #define ELEMENTAUTONUMSCHEMECOMMAND_H
 
+#include "assignvariables.h"
 #include "numerotationcontext.h"
 #include "renumberelementscommand.h"
 
@@ -201,6 +202,8 @@ class ElementAutoNumSchemeCommand : public QUndoCommand
 		static QSet<QString> labelsHeldBesides(const QETProject *project, const Element *element);
 		static NumberSupport numberSupport(const NumerotationContext &context);
 		static std::optional<int> numberOf(const NumberSupport &support, const Element *element);
+		static std::optional<int> numberOf(const NumberSupport &support,
+										   const autonum::sequentialNumbers &seq);
 		static QList<GapRange> gapRanges(const QETProject *project, const QString &title);
 		static QList<int> freeNumbers(const QETProject *project, const QString &title,
 									  const Element *element, int limit = 500);

sources/autoNum/ui/autonumberingmanagementw.cpp

@@ -175,7 +175,8 @@ void AutoNumberingManagementW::on_m_apply_folios_rb_clicked()
 		if (ui->m_from_folios_cb->count()<=0) {
 			ui->m_from_folios_cb->clear();
 			ui->m_from_folios_cb->addItem("");
-			foreach (Diagram *diagram, project_->diagrams()){
+				//Titles and positions only: folios() builds nothing
+			foreach (Diagram *diagram, project_->folios()){
 				if (diagram->title() != "")
 					ui->m_from_folios_cb->addItem(
 							diagram->title(),
@@ -206,16 +207,17 @@ void AutoNumberingManagementW::on_m_from_folios_cb_currentIndexChanged(
 	if (index > 0) {
 		ui->m_to_folios_cb->setEnabled(true);
 		ui->m_to_folios_cb->addItem("");
-		for (int i=index;i<project_->diagrams().size();i++) {
-				if (project_->diagrams().at(i)->title() != "") {
+		const QList<Diagram *> folios = project_->folios();
+		for (int i=index;i<folios.size();i++) {
+				if (folios.at(i)->title() != "") {
 					ui->m_to_folios_cb->addItem(
-						project_->diagrams().at(i)->title(),
-						project_->diagrams().at(i)->folioIndex());
+						folios.at(i)->title(),
+						folios.at(i)->folioIndex());
 				}
 				else ui->m_to_folios_cb->addItem(
 					QString::number(
-						project_->diagrams().at(i)->folioIndex()),
-							project_->diagrams().at(i)->folioIndex());
+						folios.at(i)->folioIndex()),
+							folios.at(i)->folioIndex());
 		}
 		applyEnable(true);
 		ui->m_selected_folios_le->clear();

sources/autoNum/ui/folioautonumbering.cpp

@@ -136,7 +136,8 @@ void FolioAutonumberingW::on_m_autonumber_tabs_rb_clicked()
 	if (ui->m_from_cb->count()<=0){
 		ui->m_from_cb->clear();
 		ui->m_from_cb->addItem("");
-		foreach (Diagram *diagram, project_->diagrams()){
+			//Titles only: folios() builds nothing
+		foreach (Diagram *diagram, project_->folios()){
 			ui->m_from_cb->addItem(diagram->title());
 		}
 	}
@@ -164,9 +165,9 @@ void FolioAutonumberingW::on_m_from_cb_currentIndexChanged(int)
 	ui->m_to_cb->clear();
 	if (index > 0){
 		ui->m_to_cb->setEnabled(true);
-		for (int i=index;i<project_->diagrams().size();i++)
-			ui->m_to_cb->addItem(project_
-					     ->diagrams().at(i)->title());
+		const QList<Diagram *> folios = project_->folios();
+		for (int i=index;i<folios.size();i++)
+			ui->m_to_cb->addItem(folios.at(i)->title());
 		applyEnable(true);
 	}
 	else{

sources/bordertitleblock.cpp

@@ -29,6 +29,10 @@
 #include "titleblocktemplaterenderer.h"
 
 
+#include "diagram.h"
+#include "qetproject.h"
+#include "dataBase/projectdatabase.h"
+
 #include <QLocale>
 #include <QPainter>
 #include <QRegularExpression>
@@ -282,28 +286,98 @@ void BorderTitleBlock::borderFromXml(const QDomElement &xml_elmt) {
 	@return the properties of the titleblock
 	\~French les proprietes du cartouches
 */
-TitleBlockProperties BorderTitleBlock::exportTitleBlock()
+TitleBlockProperties BorderTitleBlock::exportTitleBlock() const
+{
+	return current();
+}
+
+/**
+	@brief BorderTitleBlock::localTitleBlock
+	@return the properties of the titleblock this object holds itself,
+	whether or not its folio is placed in a project
+*/
+TitleBlockProperties BorderTitleBlock::localTitleBlock() const
 {
 	TitleBlockProperties ip;
 
-	ip.author = author();
-	ip.date = date();
-	ip.title = title();
-	ip.filename = fileName();
-	ip.plant = plant();
-	ip.locmach = locmach();
-	ip.indexrev = indexrev();
-	ip.version = version();
-	ip.folio = folio();
+	ip.author = btb_author_;
+	ip.date = btb_date_;
+	ip.title = btb_title_;
+	ip.filename = btb_filename_;
+	ip.plant = btb_plant_;
+	ip.locmach = btb_locmach_;
+	ip.indexrev = btb_indexrev_;
+	ip.version = btb_version_;
+	ip.folio = btb_folio_;
 	ip.template_name = titleBlockTemplateName();
 	ip.display_at = m_edge;
-	ip.auto_page_num = autoPageNum();
+	ip.auto_page_num = btb_auto_page_num_;
 	ip.context = additional_fields_;
 	ip.collection = QET::QetCollection::Embedded;
 
 	return(ip);
 }
 
+/**
+	@brief BorderTitleBlock::current
+	@return the properties of the titleblock: for a folio placed in a
+	project the project's store holds them (DB-ACCESSORS-PLAN.md stage
+	4.4), for any other this object's own copy.
+*/
+TitleBlockProperties BorderTitleBlock::current() const
+{
+	if (const TitleBlockProperties *s = stored())
+		return *s;
+	return localTitleBlock();
+}
+
+/**
+	@brief BorderTitleBlock::stored
+	@return the properties the project's store holds for this titleblock's
+	folio, or nullptr if it is not placed. Read at once: the getters use it
+	field by field, as label formulas ask for the folio and title of every
+	symbol's folio, and copying the whole properties each time costs.
+*/
+const TitleBlockProperties *BorderTitleBlock::stored() const
+{
+	if (projectDataBase *store = placedStore())
+		return store->storedFolioTitleBlock(m_owner_folio->uuid());
+	return nullptr;
+}
+
+/**
+	@brief BorderTitleBlock::setOwnerFolio
+	@param folio : the folio this border and title block belongs to
+*/
+void BorderTitleBlock::setOwnerFolio(Diagram *folio)
+{
+	m_owner_folio = folio;
+}
+
+/**
+	@brief BorderTitleBlock::placedStore
+	@return the project database holding this titleblock's properties, or
+	nullptr if its folio is not placed in a project
+*/
+projectDataBase *BorderTitleBlock::placedStore() const
+{
+	QETProject *project = m_owner_folio ? m_owner_folio->project() : nullptr;
+	projectDataBase *store = project ? project->dataBase() : nullptr;
+	return store && store->placedFolio(m_owner_folio->uuid()) == m_owner_folio
+			? store : nullptr;
+}
+
+/**
+	@brief BorderTitleBlock::storeTitleBlock
+	Write this titleblock's properties to its project's store, once its
+	folio is placed: every change of them comes through here.
+*/
+void BorderTitleBlock::storeTitleBlock()
+{
+	if (projectDataBase *store = placedStore())
+		store->storeFolioTitleBlock(m_owner_folio->uuid(), localTitleBlock());
+}
+
 /**
 	@brief BorderTitleBlock::importTitleBlock
 	@param ip the new properties of titleblock
@@ -333,6 +407,7 @@ void BorderTitleBlock::importTitleBlock(const TitleBlockProperties &ip)
 	// through setFolioData(),
 	// which in turn calls updateDiagramContextForTitleBlock().
 	emit(needTitleBlockTemplate(ip.template_name));
+	storeTitleBlock();
 	emit informationChanged();
 }
 
@@ -391,6 +466,7 @@ void BorderTitleBlock::setTitleBlockTemplate(
 		const TitleBlockTemplate *titleblock_template) {
 	m_titleblock_template_renderer -> setTitleBlockTemplate(
 				titleblock_template);
+	storeTitleBlock();
 }
 
 /**
@@ -889,9 +965,21 @@ DiagramPosition BorderTitleBlock::convertPosition(const QPointF &pos)
 void BorderTitleBlock::setFolio(const QString &folio)
 {
 	btb_folio_ = folio;
+	storeTitleBlock();
 	emit (titleBlockFolioChanged(folio));
 }
 
+/**
+	@brief BorderTitleBlock::setAutoPageNum
+	@param title : the title of the folio numbering this folio follows,
+	nothing else changes
+*/
+void BorderTitleBlock::setAutoPageNum(const QString &title)
+{
+	btb_auto_page_num_ = title;
+	storeTitleBlock();
+}
+
 /**
 	@brief BorderTitleBlock::updateDiagramContextForTitleBlock
 	Update the informations given to the titleblock template
@@ -915,9 +1003,10 @@ void BorderTitleBlock::updateDiagramContextForTitleBlock(
 	// So an empty page-level value is skipped only when a real project-level
 	// one is already there to show through; otherwise it still goes in
 	// empty, which is what makes the placeholder resolve to nothing.
+	const TitleBlockProperties tb = current();
 	DiagramContext context = initial_context;
-	foreach (QString key, additional_fields_.keys()) {
-		const QVariant value = additional_fields_[key];
+	foreach (QString key, tb.context.keys()) {
+		const QVariant value = tb.context[key];
 		if (!value.toString().isEmpty() || !context.contains(key))
 			context.addValue(key, value);
 	}
@@ -925,20 +1014,20 @@ void BorderTitleBlock::updateDiagramContextForTitleBlock(
 	// ... overridden by the historical and/or dynamically generated fields
 	QLocale var;
 	var.dateFormat(QLocale::ShortFormat);
-	context.addValue("author",      btb_author_);
+	context.addValue("author",      tb.author);
 	context.addValue(
 		"date",
-		QLocale::system().toString(btb_date_, QLocale::ShortFormat));
-	context.addValue("title",       btb_title_);
-	context.addValue("filename",    btb_filename_);
-	context.addValue("plant",     btb_plant_);
-	context.addValue("locmach",     btb_locmach_);
-	context.addValue("indexrev",    btb_indexrev_);
-	context.addValue("version",     btb_version_);
+		QLocale::system().toString(tb.date, QLocale::ShortFormat));
+	context.addValue("title",       tb.title);
+	context.addValue("filename",    tb.filename);
+	context.addValue("plant",     tb.plant);
+	context.addValue("locmach",     tb.locmach);
+	context.addValue("indexrev",    tb.indexrev);
+	context.addValue("version",     tb.version);
 	context.addValue("folio",       btb_final_folio_);
 	context.addValue("folio-id",    folio_index_);
 	context.addValue("folio-total", folio_total_);
-	context.addValue("auto_page_num", btb_auto_page_num_);
+	context.addValue("auto_page_num", tb.auto_page_num);
 	context.addValue("previous-folio-num", m_previous_folio_num);
 	context.addValue("next-folio-num", m_next_folio_num);
 
@@ -1041,11 +1130,12 @@ void BorderTitleBlock::setFolioData(
 
 	// regenerate the content of the folio field
 	// regenere le contenu du champ folio
-	btb_final_folio_ = btb_folio_;
+	btb_final_folio_ = folio();
 
 	if (btb_final_folio_.contains("%autonum")){
 		btb_final_folio_.replace("%autonum", autonum);
 		btb_folio_ = btb_final_folio_;
+		storeTitleBlock();
 	}
 	btb_final_folio_.replace("%id",    QString::number(folio_index_));
 	btb_final_folio_.replace("%total", QString::number(folio_total_));

sources/bordertitleblock.h

@@ -29,6 +29,8 @@ class QPainter;
 class DiagramPosition;
 class TitleBlockTemplate;
 class TitleBlockTemplateRenderer;
+class Diagram;
+class projectDataBase;
 /**
 	@brief The BorderTitleBlock class
 	This class represents the border and the titleblock which frame a
@@ -107,34 +109,36 @@ class BorderTitleBlock : public QObject
 		QRectF outsideBorderRect() const;
 		QRectF insideBorderRect() const;
 	
-		// methods to get title block basic data
+		// methods to get title block basic data. A folio placed in a
+		// project reads them from the project's store
+		// (DB-ACCESSORS-PLAN.md stage 4.4), any other from its own copy.
 		/// @return the value of the title block "Author" field
-		QString author() const { return(btb_author_); }
+		QString author() const { const TitleBlockProperties *s = stored(); return(s ? s->author : btb_author_); }
 		/// @return the value of the title block "Date" field
-		QDate date() const { return(btb_date_); }
+		QDate date() const { const TitleBlockProperties *s = stored(); return(s ? s->date : btb_date_); }
 		/// @return the value of the title block "Title" field
-		QString title() const { return(btb_title_); }
+		QString title() const { const TitleBlockProperties *s = stored(); return(s ? s->title : btb_title_); }
 		/// @return the value of the title block "Folio" field
-		QString folio() const { return(btb_folio_); }
+		QString folio() const { const TitleBlockProperties *s = stored(); return(s ? s->folio : btb_folio_); }
 		/// @return the value of the title block "Folio" field as displayed
 		QString finalfolio() const { return(btb_final_folio_); }
 		/// @return the value of the title block "Plant" field
-		QString plant() const { return(btb_plant_); }
+		QString plant() const { const TitleBlockProperties *s = stored(); return(s ? s->plant : btb_plant_); }
 		/// @return the value of the title block "Locmach" field
-		QString locmach() const { return(btb_locmach_); }
+		QString locmach() const { const TitleBlockProperties *s = stored(); return(s ? s->locmach : btb_locmach_); }
 		/// @return the value of the revision index block "Folio" field
-		QString indexrev() const { return(btb_indexrev_); }
+		QString indexrev() const { const TitleBlockProperties *s = stored(); return(s ? s->indexrev : btb_indexrev_); }
 		/// @return the value of the title block "File" field
-		QString fileName() const { return(btb_filename_); }
+		QString fileName() const { const TitleBlockProperties *s = stored(); return(s ? s->filename : btb_filename_); }
 		/// @return the value of the title block Additional Fields
-		QString version() const { return(btb_version_); }
+		QString version() const { const TitleBlockProperties *s = stored(); return(s ? s->version : btb_version_); }
 		/// @return the value of the title block Additional Fields
 		DiagramContext additionalFields() const {
-			return (additional_fields_); }
+			const TitleBlockProperties *s = stored(); return(s ? s->context : additional_fields_); }
 		/// @return the value of the title block
-		QString autoPageNum() const { return(btb_auto_page_num_); }
+		QString autoPageNum() const { const TitleBlockProperties *s = stored(); return(s ? s->auto_page_num : btb_auto_page_num_); }
 			/// The title of the folio numbering this folio follows, nothing else changes
-		void setAutoPageNum(const QString &title) { btb_auto_page_num_ = title; }
+		void setAutoPageNum(const QString &title);
 		/// @return the value of the total number of folios
 		int folioTotal() const { return(folio_total_);}
 	
@@ -175,7 +179,9 @@ class BorderTitleBlock : public QObject
 		void borderToXml(QDomElement &);
 		void borderFromXml(const QDomElement &);
 		
-		TitleBlockProperties exportTitleBlock();
+		TitleBlockProperties exportTitleBlock() const;
+		TitleBlockProperties localTitleBlock() const;
+		void setOwnerFolio(Diagram *folio);
 		void importTitleBlock(const TitleBlockProperties &);
 		BorderProperties exportBorder();
 		void importBorder(const BorderProperties &);
@@ -289,5 +295,10 @@ class BorderTitleBlock : public QObject
 		bool display_rows_ = false;
 		bool display_border_ = false;
 		TitleBlockTemplateRenderer *m_titleblock_template_renderer;
+		Diagram *m_owner_folio = nullptr;
+		TitleBlockProperties current() const;
+		const TitleBlockProperties *stored() const;
+		projectDataBase *placedStore() const;
+		void storeTitleBlock();
 };
 #endif

sources/cable/cablemanager.cpp

@@ -335,6 +335,10 @@ void CableManager::refreshLabels(QETProject *project)
 		QString label;
 	};
 
+		//Without cables, the folios not built hold nothing this pass
+		//changes but stale references (QETProject::cableLabelFolios())
+	const QList<Diagram *> folios = project->cableLabelFolios();
+
 	QHash<QUuid, Binding> bindings;
 	for (Cable *cable : project->cables())
 	{
@@ -361,7 +365,7 @@ void CableManager::refreshLabels(QETProject *project)
 		//the core or the link does.
 	QHash<QUuid, Conductor *> conductors_by_uuid;
 	QHash<Element *, QList<Conductor *>> endings_on_report;
-	for (Diagram *diagram : project->diagrams())
+	for (Diagram *diagram : folios)
 	{
 		if (!diagram) continue;
 		for (Conductor *conductor : diagram->conductors())
@@ -440,7 +444,7 @@ void CableManager::refreshLabels(QETProject *project)
 		}
 	}
 
-	for (Diagram *diagram : project->diagrams())
+	for (Diagram *diagram : folios)
 	{
 		if (!diagram) continue;
 		for (Conductor *conductor : diagram->conductors())

sources/cli_export.cpp

@@ -869,8 +869,8 @@ int exportLinks(QETProject &project, const QString &output)
 /// diff can reveal markup QET silently normalises (tolerated-but-invalid XML).
 int resaveProject(QETProject &project, const QString &output)
 {
-	const QDomDocument doc = project.toXml();
 	if (QETProject::isContainerPath(output)) {
+		const QDomDocument doc = project.toXml();
 		QString error;
 		if (!QETProject::writeContainer(doc, output, &error)) {
 			err << "Cannot write '" << output << "': " << error << "\n";
@@ -879,13 +879,17 @@ int resaveProject(QETProject &project, const QString &output)
 		out << "Re-saved project -> " << output << "\n";
 		return 0;
 	}
+		//Folios not built (QET_LAZY_FOLIOS) written as read when that is
+		//what building them would write (QETProject::toXml())
+	QHash<int, QByteArray> kept_folios;
+	const QDomDocument doc = project.toXml(&kept_folios);
 	QFile file(output);
 	if (!file.open(QIODevice::WriteOnly | QIODevice::Text)) {
 		err << "Cannot open '" << output << "' for writing.\n";
 		return 1;
 	}
 	QTextStream fout(&file);
-	fout << doc.toString(4);
+	fout << QETProject::spliceKeptFolios(doc.toString(4), kept_folios);
 	file.close();
 	out << "Re-saved project -> " << output << "\n";
 	return 0;
@@ -963,21 +967,25 @@ int setTitleBlock(QETProject &project, const QString &output,
 		++folios;
 	}
 
-	const QDomDocument doc = project.toXml();
 	if (QETProject::isContainerPath(output)) {
+		const QDomDocument doc = project.toXml();
 		QString error;
 		if (!QETProject::writeContainer(doc, output, &error)) {
 			err << "Cannot write '" << output << "': " << error << "\n";
 			return 1;
 		}
 	} else {
+			//Folios not built (QET_LAZY_FOLIOS) written as read when that is
+			//what building them would write (QETProject::toXml())
+		QHash<int, QByteArray> kept_folios;
+		const QDomDocument doc = project.toXml(&kept_folios);
 		QFile file(output);
 		if (!file.open(QIODevice::WriteOnly | QIODevice::Text)) {
 			err << "Cannot open '" << output << "' for writing.\n";
 			return 1;
 		}
 		QTextStream fout(&file);
-		fout << doc.toString(4);
+		fout << QETProject::spliceKeptFolios(doc.toString(4), kept_folios);
 		file.close();
 	}
 	out << "Stamped " << fields.size() << " field(s) on "

sources/conductorproperties.cpp

@@ -217,10 +217,22 @@ void SingleLineProperties::drawPen(QPainter *painter,
 */
 void SingleLineProperties::toXml(QDomElement &e) const
 {
-	e.setAttribute("ground",  hasGround  ? "true" : "false");
-	e.setAttribute("neutral", hasNeutral ? "true" : "false");
-	e.setAttribute("phase",   phases);
-	if (isPen()) e.setAttribute("pen", "true");
+	for (const auto &attribute : attributes())
+		e.setAttribute(attribute.first, attribute.second);
+}
+
+/**
+	@brief SingleLineProperties::attributes
+	@return the attributes toXml() writes, in its order
+*/
+QList<QPair<QString, QString>> SingleLineProperties::attributes() const
+{
+	QList<QPair<QString, QString>> a;
+	a << qMakePair(QStringLiteral("ground"), QString::fromLatin1(hasGround ? "true" : "false"));
+	a << qMakePair(QStringLiteral("neutral"), QString::fromLatin1(hasNeutral ? "true" : "false"));
+	a << qMakePair(QStringLiteral("phase"), QString::number(phases));
+	if (isPen()) a << qMakePair(QStringLiteral("pen"), QStringLiteral("true"));
+	return a;
 }
 
 /**
@@ -268,50 +280,66 @@ ConductorProperties::~ConductorProperties()
 */
 void ConductorProperties::toXml(QDomElement &e) const
 {
-	e.setAttribute("type", typeToString(type));
+	for (const auto &attribute : attributes())
+		e.setAttribute(attribute.first, attribute.second);
+}
+
+/**
+	@brief ConductorProperties::attributes
+	@return the attributes toXml() writes, in the order it writes them: the
+	project database stores a placed wire's properties as these.
+*/
+QList<QPair<QString, QString>> ConductorProperties::attributes() const
+{
+	QList<QPair<QString, QString>> a;
+	auto add = [&a](const char *name, const QString &value) {
+		a << qMakePair(QString::fromLatin1(name), value);
+	};
+	add("type", typeToString(type));
 
 	if (color != QColor(Qt::black))
-		e.setAttribute("color", color.name());
+		add("color", color.name());
 
-	e.setAttribute("bicolor", m_bicolor? "true" : "false");
-	e.setAttribute("color2", m_color_2.name());
-	e.setAttribute("dash-size", QString::number(m_dash_size));
+	add("bicolor", m_bicolor? "true" : "false");
+	add("color2", m_color_2.name());
+	add("dash-size", QString::number(m_dash_size));
 
 	if (type == Single)
-		singleLineProperties.toXml(e);
+		a << singleLineProperties.attributes();
 
-	e.setAttribute("num", text);
-	e.setAttribute("text_color", text_color.name());
-	e.setAttribute("formula", m_formula);
-	e.setAttribute("cable", m_cable);
+	add("num", text);
+	add("text_color", text_color.name());
+	add("formula", m_formula);
+	add("cable", m_cable);
 	if (!m_cable_uuid.isNull())
 	{
 			//Only written when there is a cable: a conductor which is no
 			//part of one keeps whatever cable text it had and no reference
 			//at all, so a hand written value is never mistaken for a
 			//generated one.
-		e.setAttribute("cable_uuid", m_cable_uuid.toString());
-		e.setAttribute("cable_slot", QString::number(m_cable_slot));
+		add("cable_uuid", m_cable_uuid.toString());
+		add("cable_slot", QString::number(m_cable_slot));
 	}
-	e.setAttribute("bus", m_bus);
-	e.setAttribute("function", m_function);
-	e.setAttribute("tension_protocol", m_tension_protocol);
-	e.setAttribute("conductor_color", m_wire_color);
-	e.setAttribute("conductor_section", m_wire_section);
-	e.setAttribute("numsize", QString::number(text_size));
-	e.setAttribute("condsize", QString::number(cond_size));
-	e.setAttribute("displaytext", m_show_text);
-	e.setAttribute("onetextperfolio", m_one_text_per_folio);
-	e.setAttribute("vertirotatetext", QString::number(verti_rotate_text));
-	e.setAttribute("horizrotatetext", QString::number(horiz_rotate_text));
+	add("bus", m_bus);
+	add("function", m_function);
+	add("tension_protocol", m_tension_protocol);
+	add("conductor_color", m_wire_color);
+	add("conductor_section", m_wire_section);
+	add("numsize", QString::number(text_size));
+	add("condsize", QString::number(cond_size));
+	add("displaytext", QString::number(m_show_text));
+	add("onetextperfolio", QString::number(m_one_text_per_folio));
+	add("vertirotatetext", QString::number(verti_rotate_text));
+	add("horizrotatetext", QString::number(horiz_rotate_text));
 
 	QMetaEnum me = QMetaEnum::fromType<Qt::Alignment>();
-	e.setAttribute("horizontal-alignment", me.valueToKey(m_horizontal_alignment));
-	e.setAttribute("vertical-alignment", me.valueToKey(m_vertical_alignment));
+	add("horizontal-alignment", QString::fromLatin1(me.valueToKey(m_horizontal_alignment)));
+	add("vertical-alignment", QString::fromLatin1(me.valueToKey(m_vertical_alignment)));
 
 	QString conductor_style = writeStyle();
 	if (!conductor_style.isEmpty())
-		e.setAttribute("style", conductor_style);
+		add("style", conductor_style);
+	return a;
 }
 
 

sources/conductorproperties.h

@@ -39,6 +39,7 @@ class SingleLineProperties {
 	bool isPen() const;
 	void draw(QPainter *, QET::ConductorSegmentType, const QRectF &);
 	void toXml(QDomElement &) const;
+	QList<QPair<QString, QString>> attributes() const;
 	void fromXml(QDomElement &);
 	void toSettings(QSettings &, const QString & = QString()) const;
 	void fromSettings(QSettings &, const QString & = QString());
@@ -130,6 +131,7 @@ class ConductorProperties
 
 		// methods
 		void toXml(QDomElement &) const;
+		QList<QPair<QString, QString>> attributes() const;
 		void fromXml(QDomElement &);
 		void toSettings(QSettings &, const QString & = QString()) const;
 		void fromSettings(QSettings &, const QString & = QString());

sources/dataBase/projectdatabase.h

@@ -24,9 +24,15 @@
 #include <QPointer>
 #include <QFileDialog>
 #include <QHash>
+#include <QMap>
+#include <QDomDocument>
 #include <QSet>
 #include <QUuid>
 
+#include "../diagramcontext.h"
+#include "../titleblockproperties.h"
+#include "../conductorproperties.h"
+
 class Element;
 class QETProject;
 class Diagram;
@@ -98,6 +104,62 @@ class projectDataBase : public QObject
 		QSqlDatabase database() const {return m_data_base;}
 		int excludedConductorCount() const;
 
+			//The information of every symbol placed in the project, by
+			//symbol uuid: the store each symbol's information is written
+			//through (DB-ACCESSORS-PLAN.md stage 4.1). A symbol not placed
+			//(a preview, the symbol editor) keeps its own.
+		DiagramContext elementInformation(const QUuid &element) const;
+		bool hasElementInformation(const QUuid &element) const;
+			//How many placed symbols hold @p element: more than one in a
+			//file whose symbols were copied by an old version (F100), or
+			//for a moment while a copy's uuid is renewed
+		int placedElementCount(const QUuid &element) const;
+		bool storeElementInformation(const QUuid &element, const DiagramContext &information);
+		void elementInformationChanged(Element *element, const DiagramContext &information);
+		void forgetElementInformation(const QUuid &element);
+		void elementUuidChanged(Element *element, const QUuid &old_uuid);
+			//Placed symbols whose information differs from the store's,
+			//each as "uuid: why"; empty when they all agree
+		QStringList elementInformationMismatches() const;
+
+			//The title block properties of every folio of the project, by
+			//folio uuid: the store each folio's title block is written
+			//through (DB-ACCESSORS-PLAN.md stage 4.4). A folio not in a
+			//project keeps its own.
+		TitleBlockProperties folioTitleBlock(const QUuid &folio) const;
+		const TitleBlockProperties *storedFolioTitleBlock(const QUuid &folio) const;
+		Diagram *placedFolio(const QUuid &folio) const;
+		void storeFolioTitleBlock(const QUuid &folio, const TitleBlockProperties &properties);
+		void placeFolio(Diagram *folio);
+		void folioUuidChanged(Diagram *folio, const QUuid &old_uuid);
+		QStringList folioTitleBlockMismatches() const;
+
+			//The properties of every wire placed in the project, by wire
+			//uuid: the store each wire's properties are written through
+			//(DB-ACCESSORS-PLAN.md stage 4.5). A wire not placed keeps its own.
+		ConductorProperties conductorProperties(const QUuid &conductor) const;
+		bool hasConductorProperties(const QUuid &conductor) const;
+		int placedConductorCount(const QUuid &conductor) const;
+		void conductorPropertiesStored(Conductor *conductor, const ConductorProperties &properties);
+		void conductorUuidChanged(Conductor *conductor, const QUuid &old_uuid);
+		QStringList conductorPropertiesMismatches() const;
+
+			//Fill the three stores from a project's document before its
+			//folios are built (DB-ACCESSORS-PLAN.md stage 4.6), then, once
+			//they are, say how many of those values building agreed with.
+		void prefillFromDocument(const QDomDocument &document);
+		void endPrefill(bool keep_unplaced = false);
+			//A folio of a project opened with QET_LAZY_FOLIOS is being built:
+			//its rows came from the document already, so none are written
+			//and the database is not marked changed
+		void setBuildingFolio(bool building);
+		bool isBuildingFolio() const {return m_building_folios > 0;}
+		bool rowsFromDocument() const {return m_rows_from_document;}
+		QString prefillReport() const;
+		QSet<QUuid> foliosWithUnjoinedWires() const;
+		QSet<QUuid> folioUuidsOfElements(const QSet<QUuid> &elements) const;
+		QHash<QUuid, QString> elementTypesOnFolios(const QSet<QUuid> &folios) const;
+
 		void addElement         (Element *element);
 		void removeElement      (Element *element);
 		void elementInfoChanged (Element *element);
@@ -145,6 +207,7 @@ class projectDataBase : public QObject
 		void flushElementPositions();
 		void populateElementTable();
 		void populateElementInfoTable();
+		void populateElementInfoTableFromFolios();
 		void populateDiagramInfoTable();
 		void populateConductorTable();
 		void populateLinkTable();
@@ -203,7 +266,12 @@ class projectDataBase : public QObject
 				  m_cascade_remove_element_query,
 				  m_insert_shape_query,
 				  m_insert_independent_text_query,
-				  m_insert_image_query;
+				  m_insert_image_query,
+				  m_store_remove_query,
+				  m_store_insert_query,
+				  m_remove_links_query,
+				  m_conductor_properties_insert_query,
+				  m_conductor_property_remove_query;
 
 			//Which uuid's row each drawing item last wrote, and which item
 			//wrote each row. A pasted copy is added to the folio still
@@ -222,6 +290,51 @@ class projectDataBase : public QObject
 			//sends xChanged and yChanged for every step of a drag, so the
 			//cell is written when next read, as drawing items are.
 		QList<QPointer<Element>> m_moved_elements;
+		QHash<QUuid, DiagramContext> m_element_information;
+			//The placed symbols holding each uuid: a paste or a folio copy
+			//briefly gives a copy its original's uuid, so one uuid can have
+			//two symbols until the copy's is renewed.
+		QMultiHash<QUuid, QPointer<Element>> m_placed_elements;
+		QHash<QUuid, TitleBlockProperties> m_folio_titleblocks;
+		QHash<QUuid, QPointer<Diagram>> m_placed_folios;
+		QHash<QUuid, ConductorProperties> m_conductor_properties;
+			//The rows of conductor_properties, to write only what changes
+		QHash<QUuid, QHash<QString, QString>> m_conductor_attributes;
+		QSet<QUuid> m_dirty_conductor_properties;
+		int m_building_folios = 0;
+		QSet<QUuid> m_folios_with_unjoined_wires;
+			//The folios whose rows a rebuild keeps (keepUnbuiltFolioRows())
+		QSet<Diagram *> m_kept_folios;
+			//The tables' rows were filled from the document: those of a
+			//folio not built yet are right (QET_LAZY_FOLIOS)
+		bool m_rows_from_document = false;
+		void keepUnbuiltFolioRows();
+		void restoreKeptRows(const QString &table, Diagram *folio, const QString &where);
+		void dropKeptRows();
+		bool m_changed_before_folio = false, m_blocked_before_folio = false;
+		QHash<QUuid, DiagramContext> m_prefilled_elements;
+		QHash<QUuid, TitleBlockProperties> m_prefilled_folios;
+		QHash<QUuid, ConductorProperties> m_prefilled_conductors;
+		struct PrefillTally {
+			int agree = 0, differ = 0, unplaced = 0;
+			QMap<QString, int> fields;
+		};
+		PrefillTally m_prefill_tally[3];
+		void flushConductorProperties();
+		QMultiHash<QUuid, QPointer<Conductor>> m_placed_conductors;
+		bool storeConductorProperties(const QUuid &conductor, const ConductorProperties &properties);
+		void placeConductor(Conductor *conductor);
+		void unplaceConductor(Conductor *conductor, const QUuid &uuid);
+		Conductor *otherConductorHolder(const QUuid &uuid, const Conductor *conductor) const;
+		void writeConductorRow(Conductor *conductor);
+		void removeConductorRow(const QUuid &uuid);
+		void unplaceFolio(Diagram *folio, const QUuid &uuid);
+		void placeElement(Element *element);
+		Element *otherHolder(const QUuid &uuid, const Element *element) const;
+		void writeElementRows(Element *element);
+		void queueLinks(Element *element);
+		void removeElementRows(const QUuid &uuid);
+		void unplaceElement(Element *element, const QUuid &uuid);
 
 #ifdef QET_EXPORT_PROJECT_DB
 	public:

sources/diagram.cpp

@@ -16,6 +16,7 @@
 	along with QElectroTech.  If not, see <http://www.gnu.org/licenses/>.
 */
 #include "diagram.h"
+#include "dataBase/projectdatabase.h"
 #include "autoNum/elementautonumschemecommand.h"
 
 #include "ElementsCollection/elementcollectionhandler.h"
@@ -193,6 +194,7 @@ Diagram::Diagram(QETProject *project) :
 	 * http://tech-artists.org/t/qt-properly-removing-qgraphicitems/3063
 	 */
 
+	border_and_titleblock.setOwnerFolio(this);
 	qgi_manager_ = new QGIManager(this);
 	setBackgroundBrush(Qt::white);
 	conductor_setter_ = new QGraphicsLineItem(nullptr);
@@ -767,6 +769,49 @@ void Diagram::keyReleaseEvent(QKeyEvent *e)
 	}
 }
 
+/**
+	@brief Diagram::ensureLoaded
+	Build this folio's items from the XML kept when the project was
+	opened with QET_LAZY_FOLIOS, and do for them what opening does for
+	every folio's (QETProject::folioLoaded()). Nothing for a folio built
+	already.
+*/
+void Diagram::ensureLoaded()
+{
+	if (m_deferred.isNull()) {
+		return;
+	}
+	if (m_project) {
+		m_project->buildFolios({this});
+	} else {
+		buildDeferred();
+	}
+}
+
+/**
+	@brief Diagram::buildDeferred
+	Build this folio's items from the XML kept for later, and nothing else.
+	Their rows are in the project database already, filled from the same
+	XML: building writes none.
+	@return true if there was something to build
+*/
+bool Diagram::buildDeferred()
+{
+	if (m_deferred.isNull()) {
+		return false;
+	}
+	QDomElement xml = m_deferred;
+	m_deferred = QDomElement();
+	m_kept_text.clear();
+	projectDataBase *db = m_project ? m_project->dataBase() : nullptr;
+	if (db) db->setBuildingFolio(true);
+	m_loading_deferred = true;
+	fromXml(xml, QPointF(), true, nullptr);
+	m_loading_deferred = false;
+	if (db) db->setBuildingFolio(false);
+	return true;
+}
+
 /**
 	@brief Diagram::uuid
 	@return the uuid of this diagram
@@ -801,7 +846,7 @@ bool Diagram::uuidUsedByOtherDiagram(const QUuid &uuid) const
 	if (!m_project) {
 		return false;
 	}
-	const auto diagrams = m_project->diagrams();
+	const auto diagrams = m_project->folios(); //uuids only: no need to build them
 	for (const Diagram *diagram : diagrams) {
 		if (diagram != this && diagram->m_uuid == uuid) {
 			return true;
@@ -838,7 +883,7 @@ QUuid Diagram::derivedUuid(const QDomElement &root, const QString &reason) const
 				QStringLiteral("{d5951240-154d-44d6-8277-0092a31d1920}"));
 
 	const int index = m_project
-			? m_project->diagrams().indexOf(const_cast<Diagram *>(this))
+			? m_project->folios().indexOf(const_cast<Diagram *>(this))
 			: -1;
 	const QString project_title = root.ownerDocument()
 			.documentElement()
@@ -1088,6 +1133,10 @@ QList < QSet <Conductor *> > Diagram::potentials()
 	\~French Un Document XML (QDomDocument)
 */
 QDomDocument Diagram::toXml(bool whole_content, bool is_copy_command) {
+		//A folio of a project opened with QET_LAZY_FOLIOS is written from
+		//its built items (QETProject::toXml() may write one not built as
+		//it was read instead)
+	ensureLoaded();
 	// document
 	QDomDocument document;
 
@@ -1098,120 +1147,7 @@ QDomDocument Diagram::toXml(bool whole_content, bool is_copy_command) {
 	// schema properties
 	// proprietes du schema
 	if (whole_content) {
-			//Persist the folio identity, so that a folio keeps the same uuid
-			//across save/load. Without it every load invents a new one, and
-			//nothing outside the running instance (version control, a lock,
-			//a diff tool...) can tell which folio is which.
-		dom_root.setAttribute(QStringLiteral("uuid"), m_uuid.toString());
-		border_and_titleblock.titleBlockToXml(dom_root);
-		border_and_titleblock.borderToXml(dom_root);
-
-		// Default conductor properties
-		QDomElement default_conductor =
-				document.createElement(QStringLiteral("defaultconductor"));
-		defaultConductorProperties.toXml(default_conductor);
-		dom_root.appendChild(default_conductor);
-
-		// Conductor autonum
-		if (!m_conductors_autonum_name.isEmpty()) {
-			dom_root.setAttribute(QStringLiteral("conductorAutonum"),
-						  m_conductors_autonum_name);
-		}
-
-		//Default New Element
-		dom_root.setAttribute(QStringLiteral("freezeNewElement"),
-					  m_freeze_new_elements ? QStringLiteral("true") : QStringLiteral("false"));
-
-		//Default New Conductor
-		dom_root.setAttribute(QStringLiteral("freezeNewConductor"),
-					  m_freeze_new_conductors_
-					  ? QStringLiteral("true") : QStringLiteral("false"));
-
-		//Element Folio Sequential Variables
-		if (!m_elmt_unitfolio_max.isEmpty()
-				|| !m_elmt_tenfolio_max.isEmpty()
-				|| !m_elmt_hundredfolio_max.isEmpty()) {
-			QDomElement elmtfoliosequential =
-					document.createElement(
-						QStringLiteral("elementautonumfoliosequentials"));
-			if (!m_elmt_unitfolio_max.isEmpty()) {
-				QDomElement elmtfolioseq =
-						document.createElement(
-							QStringLiteral("elementunitfolioseq"));
-				folioSequentialsToXml(&m_elmt_unitfolio_max,
-							  &elmtfolioseq,
-							  QStringLiteral("sequf_"),
-							  QStringLiteral("unitfolioseq"),
-							  &document);
-				elmtfoliosequential.appendChild(elmtfolioseq);
-			}
-			if (!m_elmt_tenfolio_max.isEmpty()) {
-				QDomElement elmtfolioseq =
-						document.createElement(
-							QStringLiteral("elementtenfolioseq"));
-				folioSequentialsToXml(&m_elmt_tenfolio_max,
-							  &elmtfolioseq,
-							  QStringLiteral("seqtf_"),
-							  QStringLiteral("tenfolioseq"),
-							  &document);
-				elmtfoliosequential.appendChild(elmtfolioseq);
-			}
-			if (!m_elmt_hundredfolio_max.isEmpty()) {
-				QDomElement elmtfolioseq =
-						document.createElement(
-							QStringLiteral("elementhundredfolioseq"));
-				folioSequentialsToXml(&m_elmt_hundredfolio_max,
-							  &elmtfolioseq,
-							  QStringLiteral("seqhf_"),
-							  QStringLiteral("hundredfolioseq"),
-							  &document);
-				elmtfoliosequential.appendChild(elmtfolioseq);
-			}
-			dom_root.appendChild(elmtfoliosequential);
-		}
-		// Conductor Folio Sequential Variables
-		if (!m_cnd_unitfolio_max.isEmpty()
-				|| !m_cnd_tenfolio_max.isEmpty() ||
-				!m_cnd_hundredfolio_max.isEmpty()) {
-			QDomElement cndfoliosequential =
-					document.createElement(
-						QStringLiteral("conductorautonumfoliosequentials"));
-			QHash<QString, QStringList>::iterator i;
-			if (!m_cnd_unitfolio_max.isEmpty()) {
-				QDomElement cndfolioseq =
-						document.createElement(
-							QStringLiteral("conductorunitfolioseq"));
-				folioSequentialsToXml(&m_cnd_unitfolio_max,
-							  &cndfolioseq,
-							  QStringLiteral("sequf_"),
-							  QStringLiteral("unitfolioseq"),
-							  &document);
-				cndfoliosequential.appendChild(cndfolioseq);
-			}
-			if (!m_cnd_tenfolio_max.isEmpty()) {
-				QDomElement cndfolioseq =
-						document.createElement(
-							QStringLiteral("conductortenfolioseq"));
-				folioSequentialsToXml(&m_cnd_tenfolio_max,
-							  &cndfolioseq,
-							  QStringLiteral("seqtf_"),
-							  QStringLiteral("tenfolioseq"),
-							  &document);
-				cndfoliosequential.appendChild(cndfolioseq);
-			}
-			if (!m_cnd_hundredfolio_max.isEmpty()) {
-				QDomElement cndfolioseq =
-						document.createElement(
-							QStringLiteral("conductorhundredfolioseq"));
-				folioSequentialsToXml(&m_cnd_hundredfolio_max,
-							  &cndfolioseq,
-							  QStringLiteral("seqhf_"),
-							  QStringLiteral("hundredfolioseq"),
-							  &document);
-				cndfoliosequential.appendChild(cndfolioseq);
-			}
-			dom_root.appendChild(cndfoliosequential);
-		}
+		writeHeader(document, dom_root);
 	}
 	else {
 		//this method with whole_content to false,
@@ -1307,8 +1243,15 @@ QDomDocument Diagram::toXml(bool whole_content, bool is_copy_command) {
 		// since those ids are assigned sequentially in element order.
 	std::stable_sort(list_elements.begin(), list_elements.end(),
 			  [](Element *a, Element *b) { return elementSortKey(a) < elementSortKey(b); });
+		//Wires that tie on their ends (common: several from one terminal)
+		//keep the order they were made in, which for a project's is its
+		//file's -- the order the scene gave them so far, except for a folio
+		//built late (QET_LAZY_FOLIOS), whose scene order differed
 	std::stable_sort(list_conductors.begin(), list_conductors.end(),
-			  [](Conductor *a, Conductor *b) { return conductorSortKey(a) < conductorSortKey(b); });
+			  [](Conductor *a, Conductor *b) {
+		const QString ka = conductorSortKey(a), kb = conductorSortKey(b);
+		return ka != kb ? ka < kb : a->creationRank() < b->creationRank();
+	});
 
 		// A copy carries the numberings its elements follow: pasted into
 		// another project, which does not know them, it can offer to import
@@ -1375,6 +1318,143 @@ QDomDocument Diagram::toXml(bool whole_content, bool is_copy_command) {
 	return(document);
 }
 
+/**
+	@brief Diagram::writeHeader
+	Write this folio's own data -- its uuid, title block, border, default
+	wire, numbering -- into @p dom_root, the folio's element of @p document:
+	what toXml() writes before the folio's items.
+*/
+void Diagram::writeHeader(QDomDocument &document, QDomElement &dom_root)
+{
+		//Persist the folio identity, so that a folio keeps the same uuid
+		//across save/load. Without it every load invents a new one, and
+		//nothing outside the running instance (version control, a lock,
+		//a diff tool...) can tell which folio is which.
+	dom_root.setAttribute(QStringLiteral("uuid"), m_uuid.toString());
+	border_and_titleblock.titleBlockToXml(dom_root);
+	border_and_titleblock.borderToXml(dom_root);
+
+	// Default conductor properties
+	QDomElement default_conductor =
+			document.createElement(QStringLiteral("defaultconductor"));
+	defaultConductorProperties.toXml(default_conductor);
+	dom_root.appendChild(default_conductor);
+
+	// Conductor autonum
+	if (!m_conductors_autonum_name.isEmpty()) {
+		dom_root.setAttribute(QStringLiteral("conductorAutonum"),
+					  m_conductors_autonum_name);
+	}
+
+	//Default New Element
+	dom_root.setAttribute(QStringLiteral("freezeNewElement"),
+				  m_freeze_new_elements ? QStringLiteral("true") : QStringLiteral("false"));
+
+	//Default New Conductor
+	dom_root.setAttribute(QStringLiteral("freezeNewConductor"),
+				  m_freeze_new_conductors_
+				  ? QStringLiteral("true") : QStringLiteral("false"));
+
+	//Element Folio Sequential Variables
+	if (!m_elmt_unitfolio_max.isEmpty()
+			|| !m_elmt_tenfolio_max.isEmpty()
+			|| !m_elmt_hundredfolio_max.isEmpty()) {
+		QDomElement elmtfoliosequential =
+				document.createElement(
+					QStringLiteral("elementautonumfoliosequentials"));
+		if (!m_elmt_unitfolio_max.isEmpty()) {
+			QDomElement elmtfolioseq =
+					document.createElement(
+						QStringLiteral("elementunitfolioseq"));
+			folioSequentialsToXml(&m_elmt_unitfolio_max,
+						  &elmtfolioseq,
+						  QStringLiteral("sequf_"),
+						  QStringLiteral("unitfolioseq"),
+						  &document);
+			elmtfoliosequential.appendChild(elmtfolioseq);
+		}
+		if (!m_elmt_tenfolio_max.isEmpty()) {
+			QDomElement elmtfolioseq =
+					document.createElement(
+						QStringLiteral("elementtenfolioseq"));
+			folioSequentialsToXml(&m_elmt_tenfolio_max,
+						  &elmtfolioseq,
+						  QStringLiteral("seqtf_"),
+						  QStringLiteral("tenfolioseq"),
+						  &document);
+			elmtfoliosequential.appendChild(elmtfolioseq);
+		}
+		if (!m_elmt_hundredfolio_max.isEmpty()) {
+			QDomElement elmtfolioseq =
+					document.createElement(
+						QStringLiteral("elementhundredfolioseq"));
+			folioSequentialsToXml(&m_elmt_hundredfolio_max,
+						  &elmtfolioseq,
+						  QStringLiteral("seqhf_"),
+						  QStringLiteral("hundredfolioseq"),
+						  &document);
+			elmtfoliosequential.appendChild(elmtfolioseq);
+		}
+		dom_root.appendChild(elmtfoliosequential);
+	}
+	// Conductor Folio Sequential Variables
+	if (!m_cnd_unitfolio_max.isEmpty()
+			|| !m_cnd_tenfolio_max.isEmpty() ||
+			!m_cnd_hundredfolio_max.isEmpty()) {
+		QDomElement cndfoliosequential =
+				document.createElement(
+					QStringLiteral("conductorautonumfoliosequentials"));
+		QHash<QString, QStringList>::iterator i;
+		if (!m_cnd_unitfolio_max.isEmpty()) {
+			QDomElement cndfolioseq =
+					document.createElement(
+						QStringLiteral("conductorunitfolioseq"));
+			folioSequentialsToXml(&m_cnd_unitfolio_max,
+						  &cndfolioseq,
+						  QStringLiteral("sequf_"),
+						  QStringLiteral("unitfolioseq"),
+						  &document);
+			cndfoliosequential.appendChild(cndfolioseq);
+		}
+		if (!m_cnd_tenfolio_max.isEmpty()) {
+			QDomElement cndfolioseq =
+					document.createElement(
+						QStringLiteral("conductortenfolioseq"));
+			folioSequentialsToXml(&m_cnd_tenfolio_max,
+						  &cndfolioseq,
+						  QStringLiteral("seqtf_"),
+						  QStringLiteral("tenfolioseq"),
+						  &document);
+			cndfoliosequential.appendChild(cndfolioseq);
+		}
+		if (!m_cnd_hundredfolio_max.isEmpty()) {
+			QDomElement cndfolioseq =
+					document.createElement(
+						QStringLiteral("conductorhundredfolioseq"));
+			folioSequentialsToXml(&m_cnd_hundredfolio_max,
+						  &cndfolioseq,
+						  QStringLiteral("seqhf_"),
+						  QStringLiteral("hundredfolioseq"),
+						  &document);
+			cndfoliosequential.appendChild(cndfolioseq);
+		}
+		dom_root.appendChild(cndfoliosequential);
+	}
+}
+
+/**
+	@brief Diagram::headerXml
+	@return the folio's own data as writeHeader() writes it, as text
+*/
+QString Diagram::headerXml()
+{
+	QDomDocument document;
+	auto dom_root = document.createElement(QStringLiteral("diagram"));
+	document.appendChild(dom_root);
+	writeHeader(document, dom_root);
+	return document.toString();
+}
+
 /**
 	@brief Diagram::folioSequentialsToXml
 	Add folio sequential to QDomElement
@@ -1692,8 +1772,9 @@ bool Diagram::fromXml(QDomElement &document,
 		return(false);
 	}
 
-		// Read attributes of this diagram
-	if (consider_informations)
+		// Read attributes of this diagram (already read for a folio whose
+		// items are built later, see ensureLoaded())
+	if (consider_informations && !m_loading_deferred)
 	{
 			// Restore the persisted folio uuid. Done first, before any item is
 			// loaded, so that everything created below sees the final uuid.
@@ -1701,6 +1782,7 @@ bool Diagram::fromXml(QDomElement &document,
 			// persisted, or uuid already taken by another folio) gets a
 			// deterministic one instead, see derivedUuid().
 		const QUuid persisted_uuid(root.attribute(QStringLiteral("uuid")));
+		const QUuid old_uuid = m_uuid;
 		if (persisted_uuid.isNull()) {
 			m_uuid = derivedUuid(root, QStringLiteral("legacy"));
 		} else if (uuidUsedByOtherDiagram(persisted_uuid)) {
@@ -1709,6 +1791,9 @@ bool Diagram::fromXml(QDomElement &document,
 		} else {
 			m_uuid = persisted_uuid;
 		}
+			//A placed folio's stored title block follows its uuid
+		if (m_project && m_project->dataBase())
+			m_project->dataBase()->folioUuidChanged(this, old_uuid);
 
 		// Load border and titleblock
 		border_and_titleblock.titleBlockFromXml(root);
@@ -1776,6 +1861,16 @@ bool Diagram::fromXml(QDomElement &document,
 		return(true);
 	}
 
+		//A project opened with QET_LAZY_FOLIOS builds a folio's items when
+		//they are first needed: until then the folio has what it says
+		//about itself (uuid, title block, border, numbering) and keeps its
+		//XML, which belongs to the project's document.
+	if (consider_informations && !m_loading_deferred && m_project
+		&& m_project->deferringFolios()) {
+		m_deferred = root;
+		return(true);
+	}
+
 		//If paste from another project
 	if (root.hasAttribute(QStringLiteral("projectId")))
 	{

sources/diagram.h

@@ -140,6 +140,11 @@ class Diagram : public QGraphicsScene
 		bool m_freeze_new_elements;
 		bool m_freeze_new_conductors_;
 		QUuid m_uuid = QUuid::createUuid();
+			/// The XML of this folio's items, while they are not built yet
+		QDomElement m_deferred;
+		QString m_opened_header;
+		QByteArray m_kept_text;
+		bool m_loading_deferred = false;
 
 			//Selection before the current click, see completeGroupSelection()
 		QList<QPointer<QGraphicsObject>> m_previous_selection;
@@ -200,10 +205,26 @@ class Diagram : public QGraphicsScene
 	
 		// methods related to XML import/export
 		QDomDocument toXml(bool wholeContent = true, bool is_copy_command = false);
+		void writeHeader(QDomDocument &document, QDomElement &dom_root);
 		bool initFromXml(QDomElement &,
 				 QPointF = QPointF(),
 				 bool = true,
 				 DiagramContent * = nullptr);
+			/// false while this folio's items wait in its XML to be
+			/// built (QET_LAZY_FOLIOS, LAZY-FOLIO-PLAN.md)
+		bool isLoaded() const {return m_deferred.isNull();}
+		QDomElement deferredXml() const {return m_deferred;}
+		QString headerXml();
+			/// The folio's text in the file it was read from, while it is
+			/// not built (QETProject::toXml())
+		QByteArray keptText() const {return m_kept_text;}
+		void setKeptText(const QByteArray &text) {m_kept_text = text;}
+			/// Remember the folio's own data as it is now, for
+			/// headerChanged() (QETProject::toXml())
+		void rememberHeader() {m_opened_header = headerXml();}
+		bool headerChanged() {return headerXml() != m_opened_header;}
+		void ensureLoaded();
+		bool buildDeferred();
 			//The last argument is only for a copy fragment: when it is
 			//given, the cable lines that fragment carries are built as
 			//well and handed back through it -- they are not part of a

sources/diagramview.cpp

@@ -1645,6 +1645,25 @@ void DiagramView::editDiagramProperties()
 	DiagramPropertiesDialog::diagramPropertiesDialog(m_diagram, diagramEditor());
 }
 
+/**
+	@brief DiagramView::buildFolio
+	Build the items of the folio this view shows, and those of the folios
+	its cross-references need, if the project was opened without them
+	(QET_LAZY_FOLIOS); then fit the view to them.
+*/
+void DiagramView::buildFolio()
+{
+	if (QETProject *project = m_diagram->project()) {
+		if (!project->unloadedFolioCount()) {
+			return;
+		}
+		project->buildFolioToShow(m_diagram);
+	} else {
+		m_diagram->ensureLoaded();
+	}
+	adjustSceneRect();
+}
+
 /**
 	@brief DiagramView::adjustSceneRect
 	Calcul and set the area of the scene visualized by this view

sources/diagramview.h

@@ -207,6 +207,7 @@ class DiagramView : public PaletteGraphicsView
 		void paste(const QPointF & = QPointF(), QClipboard::Mode = QClipboard::Clipboard);
 		void pasteHere();
 		void duplicate(const QPoint &stepOffset);
+		void buildFolio();
 		void adjustSceneRect();
 		void updateWindowTitle();
 		void resetConductors();

sources/elementprovider.cpp

@@ -30,11 +30,10 @@
 	@param prj the project where we must find element
 	@param diagram the diagram to exclude from the search
 */
-ElementProvider::ElementProvider(QETProject *prj, Diagram *diagram)
-{
-	m_diagram_list = prj->diagrams();
-	m_diagram_list.removeOne(diagram);
-}
+ElementProvider::ElementProvider(QETProject *prj, Diagram *diagram) :
+	m_project(prj),
+	m_excluded(diagram)
+{}
 
 /**
 	@brief ElementProvider::ElementProvider Constructor
@@ -44,6 +43,46 @@ ElementProvider::ElementProvider(Diagram *diag) {
 	m_diagram_list << diag;
 }
 
+/**
+	@brief ElementProvider::ElementProvider Constructor
+	@param diagrams the diagrams to search, e.g. QETProject::builtFolios()
+*/
+ElementProvider::ElementProvider(const QList<Diagram *> &diagrams) :
+	m_diagram_list(diagrams)
+{}
+
+/**
+	@brief ElementProvider::folios
+	@return the folios to search for symbols of the kinds @p kinds (free
+	ones only if @p free_only). For a project, the folios not built yet
+	(QET_LAZY_FOLIOS) holding such a symbol are built first, and only them
+	(QETProject::buildFoliosHolding()).
+*/
+QList<Diagram *> ElementProvider::folios(ElementData::Types kinds, bool free_only) const
+{
+	if (!m_project) {
+		return m_diagram_list;
+	}
+	m_project->buildFoliosHolding(kinds, free_only);
+	QList<Diagram *> list = m_project->builtFolios();
+	list.removeOne(m_excluded);
+	return list;
+}
+
+/**
+	@brief ElementProvider::allFolios
+	@return the folios to search for anything else: every one, built
+*/
+QList<Diagram *> ElementProvider::allFolios() const
+{
+	if (!m_project) {
+		return m_diagram_list;
+	}
+	QList<Diagram *> list = m_project->diagrams();
+	list.removeOne(m_excluded);
+	return list;
+}
+
 /**
 	@brief ElementProvider::FreeElement
 	Search and return the asked element corresponding with the given filter
@@ -57,16 +96,22 @@ QVector <QPointer<Element>> ElementProvider::freeElement(ElementData::Types filt
 {
 	QVector<QPointer<Element>> free_elmt;
 	QList<Element *> elmt_list;
+	const QList<Diagram *> searched = folios(filter, true);
+		//A symbol whose saved partner is on a folio not built yet
+		//(QET_LAZY_FOLIOS) is not linked yet, but is not free: it will be
+	const QSet<QUuid> waiting = m_project ? m_project->symbolsOnUnbuiltFolios()
+										  : QSet<QUuid>();
 
 		//search in all diagram
-	for (const auto &diagram_ : std::as_const(m_diagram_list))
+	for (const auto &diagram_ : std::as_const(searched))
 	{
 			//get all element in diagram d
 		elmt_list = diagram_->elements();
 		for (const auto &elmt_ : std::as_const(elmt_list))
 		{
 			if (filter & elmt_->elementData().m_type &&
-				elmt_->isFree())
+				elmt_->isFree() &&
+				!elmt_->pendingLinks().intersects(waiting))
 			{
 				free_elmt << elmt_;
 			}
@@ -86,7 +131,7 @@ QList <Element *> ElementProvider::fromUuids(QList<QUuid> uuid_list) const
 {
 	QList <Element *> found_element;
 
-	foreach (Diagram *d, m_diagram_list) {
+	foreach (Diagram *d, allFolios()) {
 		foreach(Element *elmt, d->elements()) {
 			if (uuid_list.contains(elmt->uuid())) {
 				found_element << elmt;
@@ -106,7 +151,8 @@ QList <Element *> ElementProvider::fromUuids(QList<QUuid> uuid_list) const
 QVector<QPointer<Element>> ElementProvider::find(ElementData::Types elmt_type) const
 {
 	QVector<QPointer<Element>> returned_vector;
-	for (const auto &diagram_ : std::as_const(m_diagram_list))
+	const QList<Diagram *> searched = folios(elmt_type, false);
+	for (const auto &diagram_ : std::as_const(searched))
 	{
 		const auto elmt_list = diagram_->elements();
 		for (const auto &elmt_ : elmt_list)
@@ -153,7 +199,7 @@ QVector<QetGraphicsTableItem *> ElementProvider::table(
 		}
 	}
 
-	for (auto d : m_diagram_list) {
+	for (auto d : allFolios()) {
 		for (auto item_ : d->items())
 		{
 			if(item_->type() == QetGraphicsTableItem::Type)
@@ -197,8 +243,9 @@ QetGraphicsTableItem *ElementProvider::tableFromUuid(const QUuid &uuid)
 QVector<TerminalElement *> ElementProvider::freeTerminal() const
 {
 	QVector<TerminalElement *> vector_;
+	const QList<Diagram *> searched = folios(ElementData::Terminal, false);
 
-	for (const auto &diagram : std::as_const(m_diagram_list))
+	for (const auto &diagram : std::as_const(searched))
 	{
 		const auto elmt_list{diagram->elements()};
 

sources/elementprovider.h

@@ -41,6 +41,7 @@ class ElementProvider
 	public:
 		ElementProvider(QETProject *prj, Diagram *diagram=nullptr);
 		ElementProvider(Diagram *diag);
+		explicit ElementProvider(const QList<Diagram *> &diagrams);
 		QVector <QPointer<Element>> freeElement(ElementData::Types filter) const;
 		QList <Element *> fromUuids(QList <QUuid>) const;
 		QVector<QPointer<Element> > find(ElementData::Types elmt_type) const;
@@ -49,7 +50,15 @@ class ElementProvider
 		QVector<TerminalElement *> freeTerminal() const;
 
 	private:
+		QList<Diagram *> folios(ElementData::Types kinds, bool free_only) const;
+		QList<Diagram *> allFolios() const;
+
 		QList <Diagram *> m_diagram_list;
+			//Searching a project: its folios are asked for when searched,
+			//so that a project opened with QET_LAZY_FOLIOS builds only
+			//those a search can find something on
+		QETProject *m_project = nullptr;
+		Diagram *m_excluded = nullptr;
 };
 
 #endif // ELEMENTPROVIDER_H

sources/elementspanelwidget.cpp

@@ -473,14 +473,16 @@ void ElementsPanelWidget::updateButtons()
 		if (!selected_diagrams.isEmpty()) {
 			QETProject *selected_diagram_project = selected_diagrams.first() -> project();
 			bool is_writable           = !(selected_diagram_project -> isReadOnly());
-			int project_diagrams_count = selected_diagram_project -> diagrams().count();
+				//Positions only: folios() does not build the folios' items
+			const QList<Diagram *> folios = selected_diagram_project -> folios();
+			int project_diagrams_count = folios.count();
 
 			// Find the highest (min) and lowest (max) index among the selection
 			int min_position = project_diagrams_count;
 			int max_position = -1;
 
 			for (Diagram *diagram : selected_diagrams) {
-				int pos = selected_diagram_project -> diagrams().indexOf(diagram);
+				int pos = folios.indexOf(diagram);
 				if (pos < min_position) min_position = pos;
 				if (pos > max_position) max_position = pos;
 			}

sources/genericpanel.cpp

@@ -253,11 +253,13 @@ QTreeWidgetItem *GenericPanel::fillProjectItem(QTreeWidgetItem *project_qtwi,
 				this,&GenericPanel::projectDiagramsOrderChanged);
 		} else {
 			// remove diagrams unknown to the project (presumably removed)
-			removeObsoleteItems(project -> diagrams(),
+			removeObsoleteItems(project -> folios(),
 					    project_qtwi, QET::Diagram, false);
 		}
 		int index = 0;
-		foreach (Diagram *diagram, project -> diagrams()) {
+			//A folio's entry shows its own data (title, folio label):
+			//folios(), which does not build the folios' items
+		foreach (Diagram *diagram, project -> folios()) {
 			QTreeWidgetItem *diagram_qtwi = addDiagram(diagram,
 								   nullptr,
 								   options);

sources/print/projectprintwindow.cpp

@@ -208,7 +208,7 @@ void ProjectPrintWindow::requestPaint()
 			#endif
 		#endif
 
-	if (!m_project->diagrams().count()) {
+	if (!m_project->folios().count()) {
 		return;
 	}
 

sources/projectview.cpp

@@ -959,7 +959,9 @@ void ProjectView::loadDiagrams()
 {
 	if (!m_project) return;
 
-	setDisplayFallbackWidget(m_project -> diagrams().isEmpty());
+		//The folios' items are built when their tab is first shown
+		//(tabChanged()), not here: a tab needs only the folio's own data
+	setDisplayFallbackWidget(m_project -> folios().isEmpty());
 
 	auto dialog = DialogWaiting::instance();
 	if(dialog)
@@ -968,7 +970,7 @@ void ProjectView::loadDiagrams()
 												"...</b><br/>Creating sheet tabs :</p>"));
 	}
 
-	for(auto diagram : m_project->diagrams())
+	for(auto diagram : m_project->folios())
 	{
 		if(dialog)
 		{
@@ -1202,6 +1204,12 @@ void ProjectView::rebuildDiagramsMap()
 */
 void ProjectView::tabChanged(int tab_id)
 {
+		//A folio opened without its items (QET_LAZY_FOLIOS) is built when
+		//its tab is first shown. Read the tab itself: the first tab is
+		//shown while loadDiagrams() is still filling m_diagram_ids
+	if (auto dv = qobject_cast<DiagramView *>(m_tab->widget(tab_id)))
+		dv->buildFolio();
+
 	if (tab_id == -1)
 		setDisplayFallbackWidget(true);
 	else if(m_tab->count() == 1)

sources/qet.cpp

@@ -770,6 +770,15 @@ bool QET::compareCanonicalFilePaths(const QString &first, const QString &second)
 	@return false if an error occurred, true otherwise
 */
 bool QET::writeXmlFile(QDomDocument &xml_doc, const QString &filepath, QString *error_message)
+{
+	return writeXmlText(xml_doc.toString(4), filepath, error_message);
+}
+
+/**
+	@brief QET::writeXmlText
+	writeXmlFile() for a document already written as @p text
+*/
+bool QET::writeXmlText(const QString &text, const QString &filepath, QString *error_message)
 {
 	QSaveFile file(filepath);
 
@@ -789,7 +798,7 @@ bool QET::writeXmlFile(QDomDocument &xml_doc, const QString &filepath, QString *
 	QTextStream out(&file);
 	out.setEncoding(QStringConverter::Utf8);
 	out.setGenerateByteOrderMark(false);
-	out << xml_doc.toString(4);
+	out << text;
 	if  (!file.commit())
 	{
 		if (error_message) {
@@ -895,6 +904,15 @@ QActionGroup *QET::depthActionGroup(QObject *parent)
 }
 
 bool QET::writeToFile(QDomDocument &xml_doc, QFile *file, QString *error_message)
+{
+	return writeTextToFile(xml_doc.toString(4), file, error_message);
+}
+
+/**
+	@brief QET::writeTextToFile
+	writeToFile() for a document already written as @p text
+*/
+bool QET::writeTextToFile(const QString &text, QFile *file, QString *error_message)
 {
 	bool opened_here = file->isOpen() ? false : true;
 
@@ -920,7 +938,7 @@ bool QET::writeToFile(QDomDocument &xml_doc, QFile *file, QString *error_message
 	out.seek(0);
 	out.setEncoding(QStringConverter::Utf8);
 	out.setGenerateByteOrderMark(false);
-	out << xml_doc.toString(4);
+	out << text;
 	if (opened_here) {
 		file->close();
 	}

sources/qet.h

@@ -202,6 +202,8 @@ namespace QET {
 	bool compareCanonicalFilePaths(const QString &, const QString &);
 	bool writeXmlFile(QDomDocument &xml_doc, const QString &filepath, QString * error_message= nullptr);
 	bool writeToFile (QDomDocument &xml_doc, QFile *file, QString *error_message = nullptr);
+	bool writeXmlText(const QString &text, const QString &filepath, QString *error_message = nullptr);
+	bool writeTextToFile(const QString &text, QFile *file, QString *error_message = nullptr);
 	bool eachStrIsEqual (const QStringList &qsl);
 	QActionGroup *depthActionGroup(QObject *parent = nullptr);
 	void saveCustomColors();

sources/qetdiagrameditor.cpp

@@ -562,8 +562,9 @@ void QETDiagramEditor::setUpActions()
 	m_draw_grid->setCheckable(true);
 	m_draw_grid->setChecked(settings.value("diagrameditor/grid_display_startup", true).toBool());
 	connect(m_draw_grid, &QAction::triggered, [this](bool checked) {
+			//The folio's own setting: folios() builds nothing
 		foreach (ProjectView *prjv, this->openedProjects())
-			foreach (Diagram *d, prjv->project()->diagrams()) {
+			foreach (Diagram *d, prjv->project()->folios()) {
 				d->setDisplayGrid(checked);
 				d->update();
 			}
@@ -603,8 +604,9 @@ void QETDiagramEditor::setUpActions()
 	m_draw_guides->setCheckable(true);
 	m_draw_guides->setChecked(settings.value("diagrameditor/guides_display_startup", false).toBool());
 	connect(m_draw_guides, &QAction::triggered, [this](bool checked) {
+			//The folio's own setting: folios() builds nothing
 		foreach (ProjectView *prjv, this->openedProjects())
-			foreach (Diagram *d, prjv->project()->diagrams()) {
+			foreach (Diagram *d, prjv->project()->folios()) {
 				d->setDisplayGuides(checked);
 			}
 	});
@@ -652,8 +654,10 @@ void QETDiagramEditor::setUpActions()
 		action->setData(int(kind.first));
 		connect(action, &QAction::triggered, this, [kind](bool checked) {
 			ShownKinds::setShown(kind.first, checked);
+				//Items built later are shown or hidden as they are made
+				//(ShownKinds::tag())
 			for (QETProject *project : QETApp::registeredProjects())
-				for (Diagram *diagram : project->diagrams())
+				for (Diagram *diagram : project->builtFolios())
 					ShownKinds::apply(diagram, kind.first);
 			emit QETApp::instance()->shownKindsChanged();
 		});
@@ -2004,7 +2008,7 @@ bool QETDiagramEditor::openAndAddProject(
 		//was not found: they would otherwise vanish on the next save
 		//without the user ever being told.
 	QStringList lost_wires;
-	for (Diagram *diagram : project->diagrams()) {
+	for (Diagram *diagram : project->foliosWithWiresNotReconnected()) {
 		for (const QString &wire : diagram->wiresNotReconnected()) {
 			lost_wires << tr("Sheet %1: %2").arg(diagram->folioIndex() + 1).arg(wire);
 		}

sources/qetgraphicsitem/ViewItem/projectdbmodel.cpp

@@ -37,7 +37,8 @@
 */
 ProjectDBModel::ProjectDBModel(QETProject *project, QObject *parent) :
 	QAbstractTableModel(parent),
-	m_project(project)
+	m_project(project),
+	m_fill_when_built(project->dataBase()->isBuildingFolio())
 {
 	connect(m_project->dataBase(), &projectDataBase::dataBaseUpdated, this, &ProjectDBModel::dataBaseUpdated);
 }
@@ -320,6 +321,21 @@ void ProjectDBModel::setIdentifier(const QString &identifier) {
 	m_identifier = identifier;
 }
 
+/**
+	@brief ProjectDBModel::folioBuilt
+	The folio of a table made while it was being built (QET_LAZY_FOLIOS)
+	is built: read the database, as opening does once it has filled it.
+	Nothing for any other model.
+*/
+void ProjectDBModel::folioBuilt()
+{
+	if (!m_fill_when_built) {
+		return;
+	}
+	m_fill_when_built = false;
+	dataBaseUpdated();
+}
+
 /**
 	@brief ProjectDBModel::dataBaseUpdated
 	slot called when the project database is updated
@@ -374,6 +390,13 @@ void ProjectDBModel::setHeaderString()
 void ProjectDBModel::fillValue()
 {
 	m_record.clear();
+		//Opening builds a table before the database is filled, and fills
+		//it after: a table on a folio built late (QET_LAZY_FOLIOS) does
+		//the same, so that it is laid out as it would have been on
+		//opening -- empty until its folio is built (folioBuilt())
+	if (m_fill_when_built) {
+		return;
+	}
 	
 	auto query_ = m_project->dataBase()->newQuery(m_query);
 	if (!query_.exec()) {

sources/qetgraphicsitem/ViewItem/projectdbmodel.h

@@ -71,6 +71,7 @@ class ProjectDBModel : public QAbstractTableModel
 		void setIdentifier(const QString &identifier);
 		QString identifier() const {return m_identifier;}
 		static QString xmlTagName() {return QString("project_data_base_model");}
+		void folioBuilt();
 
 	private:
 		void dataBaseUpdated();
@@ -79,6 +80,7 @@ class ProjectDBModel : public QAbstractTableModel
 
 	private:
 		QPointer<QETProject> m_project;
+		bool m_fill_when_built = false;
 		QString m_query;
 		QVector<QStringList> m_record;
 		//First int = section, second int = Qt::role, QVariant = value

sources/qetgraphicsitem/ViewItem/qetgraphicstableitem.cpp

@@ -565,15 +565,34 @@ void QetGraphicsTableItem::initLink()
 {
 	if (!m_pending_previous_table_uuid.isNull())
 	{
-		ElementProvider provider_(this->diagram()->project());
-		if (auto previous_table = provider_.tableFromUuid(m_pending_previous_table_uuid)) {
+			//The built folios only: a previous table on a folio not built
+			//yet (QET_LAZY_FOLIOS) is linked when that folio is
+		QETProject *project = this->diagram()->project();
+		ElementProvider provider_(project->builtFolios());
+		auto previous_table = provider_.tableFromUuid(m_pending_previous_table_uuid);
+		if (previous_table) {
 			setPreviousTable(previous_table);
 		}
-		m_pending_previous_table_uuid = QUuid(); //Set to null in case initLink is called again
+		if (previous_table || !project->unloadedFolioCount()) {
+			m_pending_previous_table_uuid = QUuid(); //Set to null in case initLink is called again
+		}
 	}
 	setSize(m_pending_size);
 }
 
+/**
+	@brief QetGraphicsTableItem::previousTableUuid
+	@return the uuid of the table before this one in its chain, linked or
+	still waiting for its folio to be built (QET_LAZY_FOLIOS); null if none
+*/
+QUuid QetGraphicsTableItem::previousTableUuid() const
+{
+	if (m_previous_table) {
+		return m_previous_table->uuid();
+	}
+	return m_pending_previous_table_uuid;
+}
+
 /**
 	@brief QetGraphicsTableItem::minimumRowHeight
 	@return the minimum height of a row
@@ -610,7 +629,7 @@ QDomElement QetGraphicsTableItem::toXml(QDomDocument &dom_document) const
 	const auto project_ = diagram() ? diagram()->project() : nullptr;
 	auto in_project = [project_](const QetGraphicsTableItem *table) {
 		return project_ && table->diagram()
-				&& project_->diagrams().contains(table->diagram());
+				&& project_->folios().contains(table->diagram());
 	};
 	QetGraphicsTableItem *previous_ = m_previous_table;
 	while (previous_ && !in_project(previous_)) {

sources/qetgraphicsitem/ViewItem/qetgraphicstableitem.h

@@ -84,6 +84,8 @@ class QetGraphicsTableItem : public QetGraphicsItem
 		QPointer<QetGraphicsTableItem> nextTable() const;
 		void setToMinimumHeight();
 		void initLink();
+		bool hasPendingLink() const {return !m_pending_previous_table_uuid.isNull();}
+		QUuid previousTableUuid() const;
 		QUuid uuid() const {return m_uuid;}
 		int minimumRowHeight() const;
 

sources/qetgraphicsitem/conductor.cpp

@@ -25,6 +25,7 @@
 #include "../conductorsegment.h"
 #include "../conductorsegmentprofile.h"
 #include "../diagram.h"
+#include "../dataBase/projectdatabase.h"
 #include "../diagramcommands.h"
 #include "../qetdiagrameditor.h"
 #include "../qetgraphicsitem/terminal.h"
@@ -118,6 +119,8 @@ Conductor::Conductor(Terminal *p1, Terminal* p2) :
 	setZValue(11);
 	m_previous_z_value = zValue();
 	m_uuid = QUuid::createUuid();
+	static quint64 created = 0;
+	m_creation_rank = ++created;
 
 		//Add this conductor to the list of conductors of each of the two terminals
 	bool ajout_p1 = terminal1 -> addConductor(this);
@@ -1114,6 +1117,7 @@ void Conductor::pointsToSegments(const QList<QPointF>& points_list) {
 */
 bool Conductor::fromXml(QDomElement &dom_element)
 {
+	const QUuid old_uuid = m_uuid;
 		//Older project files have no conductor uuid attribute at all --
 		//generate one on load, same treatment terminal uuids got when
 		//that field was introduced (see terminal1/terminal2 handling in
@@ -1129,6 +1133,7 @@ bool Conductor::fromXml(QDomElement &dom_element)
 			//single load-and-resave (see #754).
 		m_uuid = QUuid::createUuid();
 	}
+	uuidChanged(old_uuid);
 
 		//"nan" and "inf" parse as numbers; a non-finite position is kept at 0
 	const qreal x = dom_element.attribute("x", nullptr).toDouble();
@@ -1235,7 +1240,7 @@ QDomElement Conductor::toXml(QDomDocument &dom_document,
 	dom_element.appendChild(dom_seq);
 
 		// Export the properties and text
-	m_properties. toXml(dom_element);
+	properties().toXml(dom_element);
 	if(m_text_item->wasMovedByUser())
 	{
 		dom_element.setAttribute("userx", QString::number(m_text_item->pos().x()));
@@ -1735,6 +1740,7 @@ void Conductor::refreshText()
 				m_properties.text = m_properties.m_formula;
 				m_text_item->setPlainText(m_properties.text);
 			}
+			storeProperties();
 		}
 		else
 		{
@@ -1833,6 +1839,7 @@ void Conductor::setProperties(const ConductorProperties &property)
 	calculateTextItemPosition();
 	update();
 
+	storeProperties();
 	emit propertiesChange();
 }
 
@@ -1842,9 +1849,75 @@ void Conductor::setProperties(const ConductorProperties &property)
 */
 ConductorProperties Conductor::properties() const
 {
+	if (projectDataBase *store = placedStore())
+		return store->conductorProperties(m_uuid);
 	return(m_properties);
 }
 
+/**
+	@brief Conductor::placedStore
+	@return the project database holding this wire's properties
+	(DB-ACCESSORS-PLAN.md stage 4.5), or nullptr if it is not placed in a
+	project, or shares its uuid with another wire for the moment a copy
+	takes to get its own
+*/
+projectDataBase *Conductor::placedStore() const
+{
+	Diagram *d = diagram();
+	QETProject *project = d ? d->project() : nullptr;
+	projectDataBase *store = project ? project->dataBase() : nullptr;
+	return store && store->hasConductorProperties(m_uuid)
+			&& store->placedConductorCount(m_uuid) == 1 ? store : nullptr;
+}
+
+/**
+	@brief Conductor::storeProperties
+	Write this wire's properties to its project's store, once it is placed:
+	every change of a placed wire's properties comes through here.
+*/
+void Conductor::storeProperties()
+{
+	Diagram *d = diagram();
+	QETProject *project = d ? d->project() : nullptr;
+	if (project && project->dataBase() && project->dataBase()->hasConductorProperties(m_uuid))
+		project->dataBase()->conductorPropertiesStored(this, m_properties);
+}
+
+/**
+	@brief Conductor::newUuid
+	Make a new uuid for this conductor; its stored properties and its row
+	follow it.
+*/
+void Conductor::newUuid()
+{
+	setUuid(QUuid::createUuid());
+}
+
+/**
+	@brief Conductor::setUuid
+	@param uuid : the uuid of this conductor, saved from now on
+*/
+void Conductor::setUuid(const QUuid &uuid)
+{
+	const QUuid old_uuid = m_uuid;
+	m_uuid = uuid;
+	m_persist_uuid = true;
+	uuidChanged(old_uuid);
+}
+
+/**
+	@brief Conductor::uuidChanged
+	Tell the project's store this placed wire's uuid changed from
+	@p old_uuid (a paste renews it, a file gives it).
+*/
+void Conductor::uuidChanged(const QUuid &old_uuid)
+{
+	Diagram *d = diagram();
+	QETProject *project = d ? d->project() : nullptr;
+	if (project && project->dataBase())
+		project->dataBase()->conductorUuidChanged(this, old_uuid);
+}
+
 /**
 	@brief Conductor::setCableReference
 	Record the cable core this conductor shows, together with the label
@@ -1868,6 +1941,7 @@ void Conductor::setCableReference(const QString &label,
 	m_properties.m_cable = label;
 	m_properties.m_cable_uuid = cable_uuid;
 	m_properties.m_cable_slot = slot;
+	storeProperties();
 	emit propertiesChange();
 }
 

sources/qetgraphicsitem/conductor.h

@@ -27,6 +27,7 @@
 class ConductorProfile;
 class ConductorSegmentProfile;
 class Diagram;
+class projectDataBase;
 class Terminal;
 class ConductorSegment;
 class ConductorTextItem;
@@ -80,8 +81,8 @@ class Conductor : public QGraphicsObject
 		Diagram *diagram() const;
 		ConductorTextItem *textItem() const;
 		QUuid uuid() const {return m_uuid;}
-		void newUuid() {m_uuid = QUuid::createUuid(); m_persist_uuid = true;}	//create new uuid for this conductor
-		void setUuid(const QUuid &uuid) {m_uuid = uuid; m_persist_uuid = true;}	//saved from now on
+		void newUuid();	//create new uuid for this conductor
+		void setUuid(const QUuid &uuid);	//saved from now on
 		void updatePath(const QRectF & = QRectF());
 
 		//This method do nothing, it's only made to be used with Q_PROPERTY
@@ -125,6 +126,11 @@ class Conductor : public QGraphicsObject
 				bool only_text = false);
 		void setProperties(const ConductorProperties &property);
 		ConductorProperties properties() const;
+			/// This wire's own copy of its properties, whatever the store holds
+		ConductorProperties ownProperties() const {return m_properties;}
+			/// The order wires were made in this session: a project's are
+			/// made in the order its file lists them
+		quint64 creationRank() const {return m_creation_rank;}
 			/// Records which cable core this conductor shows and writes the
 			/// label that assignment generates (15W1:br) into its cable
 			/// field. Deliberately not routed through
@@ -233,6 +239,10 @@ class Conductor : public QGraphicsObject
 			/// file had none -- toXml() must not persist that value, or
 			/// every reload mints and saves a new random one (see #754).
 		bool m_persist_uuid = true;
+		quint64 m_creation_rank = 0;
+		void uuidChanged(const QUuid &old_uuid);
+		projectDataBase *placedStore() const;
+		void storeProperties();
 
 			/// QPen et QBrush objects used to draw conductors
 		static QPen conductor_pen;

sources/qetgraphicsitem/element.cpp

@@ -18,6 +18,7 @@
 #include "element.h"
 #include "../qetapp.h"
 #include "../qetproject.h"
+#include "../dataBase/projectdatabase.h"
 #include "../PropertiesEditor/propertieseditordialog.h"
 #include "../autoNum/assignvariables.h"
 #include "../autoNum/elementautonumschemecommand.h"
@@ -718,6 +719,7 @@ bool Element::buildFromXml(const QDomElement &xml_def_elmt, int *state)
 	m_data.m_informations.fromXml(
 				xml_def_elmt.firstChildElement(QStringLiteral("elementInformations")),
 				QStringLiteral("elementInformation"));
+	storeInformation();
 
 		//scroll of the Children of the Definition: Parts of the Drawing
 	int parsed_elements_count = 0;
@@ -1042,7 +1044,9 @@ bool Element::fromXml(QDomElement &e,
 	}
 
 	//uuid of this element
-	m_uuid = QUuid(e.attribute(QStringLiteral("uuid"), QUuid::createUuid().toString()));
+	//Through setUuid(): a folio adds a symbol before reading it, so its
+	//stored information has to follow from the uuid it was born with.
+	setUuid(QUuid(e.attribute(QStringLiteral("uuid"), QUuid::createUuid().toString())));
 
 		//load prefix
 	m_prefix = e.attribute(QStringLiteral("prefix"));
@@ -1265,10 +1269,11 @@ QDomElement Element::toXml(
 	}
 
 	//save information of this element
-	if (! m_data.m_informations.keys().isEmpty()) {
+	const DiagramContext informations = elementInformations();
+	if (! informations.keys().isEmpty()) {
 		QDomElement infos =
 				document.createElement(QStringLiteral("elementInformations"));
-		m_data.m_informations.toXml(infos, QStringLiteral("elementInformation"));
+		informations.toXml(infos, QStringLiteral("elementInformation"));
 			//toXml() skips empty values: an element whose information is
 			//all empty would otherwise be written an empty block, which the
 			//next load reads as no information and the next save drops.
@@ -1625,7 +1630,10 @@ void Element::initLink(QETProject *prj)
 		// if nothing to link return now
 	if (tmp_uuids_link.isEmpty()) return;
 
-	ElementProvider ep(prj);
+		//The built folios only: a partner on a folio not built yet
+		//(QET_LAZY_FOLIOS) is linked when its folio is, and the saved list
+		//is kept until then, for the order it gives
+	ElementProvider ep(prj->builtFolios());
 	QList<QUuid> uuids;
 	for (const auto &linkInfo : tmp_uuids_link) {
 		uuids.append(linkInfo.uuid);
@@ -1643,7 +1651,27 @@ void Element::initLink(QETProject *prj)
 		}
 	}
 	restoreSavedLinkOrder();
-	tmp_uuids_link.clear();
+	if (pendingLinks().isEmpty() || !prj->unloadedFolioCount()) {
+		tmp_uuids_link.clear();
+	}
+}
+
+/**
+	@brief Element::pendingLinks
+	@return the uuids of the partners this symbol was saved linked to and
+	is not linked to yet: those on a folio not built yet (QET_LAZY_FOLIOS),
+	until initLink() runs again once it is
+*/
+QSet<QUuid> Element::pendingLinks() const
+{
+	QSet<QUuid> pending;
+	for (const auto &link_info : tmp_uuids_link) {
+		pending.insert(link_info.uuid);
+	}
+	for (Element *elmt : connected_elements) {
+		pending.remove(elmt->uuid());
+	}
+	return pending;
 }
 
 /**
@@ -1674,6 +1702,23 @@ void Element::initLink(const QList<Element *> &candidates)
 	tmp_uuids_link.clear();
 }
 
+/**
+	@brief Element::waitingLinks
+	@return pendingLinks() in the order this symbol was saved with them,
+	each with its group index (-1 for none)
+*/
+QList<std::pair<QUuid, int>> Element::waitingLinks() const
+{
+	const QSet<QUuid> pending = pendingLinks();
+	QList<std::pair<QUuid, int>> list;
+	for (const auto &link_info : tmp_uuids_link) {
+		if (pending.contains(link_info.uuid)) {
+			list.append({link_info.uuid, link_info.group_index});
+		}
+	}
+	return list;
+}
+
 /**
 	@brief Element::restoreSavedLinkOrder
 	Put connected_elements back in the order tmp_uuids_link saved them.
@@ -1795,6 +1840,33 @@ void Element::setFormulaSchemeId(const QUuid &id)
 		m_data.m_informations.addValue(QETInformation::ELMT_FORMULA_ID,
 									   id.toString(), false);
 	}
+	storeInformation();
+}
+
+/**
+	@brief Element::setUuid
+	A placed symbol's stored information and its database rows follow its
+	uuid (a paste or a folio copy renews it).
+*/
+void Element::setUuid(const QUuid &uuid)
+{
+	const QUuid old_uuid = m_uuid;
+	m_uuid = uuid;
+	if (diagram() && diagram()->project() && diagram()->project()->dataBase())
+		diagram()->project()->dataBase()->elementUuidChanged(this, old_uuid);
+}
+
+/**
+	@brief Element::storeInformation
+	Write this symbol's information to its project's store, once it is
+	placed (DB-ACCESSORS-PLAN.md stage 4.1): every change of a placed
+	symbol's information comes through here.
+*/
+void Element::storeInformation()
+{
+	if (diagram() && diagram()->project() && diagram()->project()->dataBase()
+		&& diagram()->project()->dataBase()->hasElementInformation(m_uuid))
+		diagram()->project()->dataBase()->elementInformationChanged(this, m_data.m_informations);
 }
 
 void Element::setElementInformations(DiagramContext dc)
@@ -1811,6 +1883,7 @@ void Element::setElementInformations(DiagramContext dc)
 	if (!actual_label.isEmpty()) {
 		m_data.m_informations.addValue(QStringLiteral("label"), actual_label); //Update the label if there is a formula
 	}
+	storeInformation();
 	emit elementInfoChange(old_info, m_data.m_informations);
 
 	// Propagate label change to linked PLC slaves (label is changed via
@@ -1841,9 +1914,43 @@ void Element::setElementInformations(DiagramContext dc)
  */
 ElementData Element::elementData() const
 {
+	if (projectDataBase *store = placedStore()) {
+		ElementData data = m_data;
+		data.m_informations = store->elementInformation(m_uuid);
+		return data;
+	}
 	return m_data;
 }
 
+/**
+	@brief Element::elementInformations
+	@return this symbol's information: for a placed symbol the project's
+	store holds it (DB-ACCESSORS-PLAN.md stage 4.2), for one not placed
+	(a preview, the symbol editor) its own copy.
+*/
+DiagramContext Element::elementInformations() const
+{
+	if (projectDataBase *store = placedStore())
+		return store->elementInformation(m_uuid);
+	return m_data.m_informations;
+}
+
+/**
+	@brief Element::placedStore
+	@return the project database holding this symbol's information, or
+	nullptr if it is not placed in a project
+*/
+projectDataBase *Element::placedStore() const
+{
+	Diagram *d = diagram();
+	QETProject *project = d ? d->project() : nullptr;
+	projectDataBase *store = project ? project->dataBase() : nullptr;
+		//A uuid other placed symbols share (F100) names no single symbol's
+		//information: this one answers from its own copy.
+	return store && store->hasElementInformation(m_uuid)
+			&& store->placedElementCount(m_uuid) == 1 ? store : nullptr;
+}
+
 /**
  * @brief Element::setElementData
  * Set new data for this element.
@@ -1860,6 +1967,7 @@ void Element::setElementData(ElementData data)
 
 	if (old_info != m_data.m_informations) {
 		m_data.m_informations.addValue(QStringLiteral("label"), actualLabel()); //Update the label if there is a formula
+		storeInformation();
 		if (diagram()) {
 			diagram()->project()->dataBase()->elementInfoChanged(this);
 		}
@@ -2078,6 +2186,7 @@ void Element::setUpFormula(bool code_letter, QUndoCommand *parent_undo)
 				->elementAutoNumCurrentFormula();
 
 		m_data.m_informations.addValue(QStringLiteral("formula"), formula);
+		storeInformation();
 
 		QString element_currentAutoNum = diagram()
 				->project()
@@ -2146,6 +2255,7 @@ void Element::setUpFormula(bool code_letter, QUndoCommand *parent_undo)
 		{
 			DiagramContext dc = m_data.m_informations;
 			m_data.m_informations.addValue(QStringLiteral("label"), actualLabel());
+			storeInformation();
 			emit elementInfoChange(dc, m_data.m_informations);
 		}
 	}
@@ -2199,6 +2309,8 @@ void Element::freezeNewAddedElement()
 */
 QString Element::actualLabel()
 {
+		//The symbol's own copy, not the store: this runs while the
+		//information is being changed, before the store has the change.
 	if (m_data.m_informations.value(QStringLiteral("formula")).toString().isEmpty()) {
 		return m_data.m_informations.value(QStringLiteral("label")).toString();
 	} else {

sources/qetgraphicsitem/element.h

@@ -40,6 +40,8 @@ class QUndoCommand;
 /**
 	This is the base class for electrical elements.
 */
+class projectDataBase;
+
 class Element : public QetGraphicsItem
 {
 	friend class DiagramEventAddElement;
@@ -130,8 +132,9 @@ class Element : public QetGraphicsItem
 		}
 
 			//METHODS related to information
-		DiagramContext elementInformations()const
-		{return m_data.m_informations;}
+		DiagramContext elementInformations()const;
+			/// This symbol's own copy of its information, whatever the store holds
+		DiagramContext ownInformations() const {return m_data.m_informations;}
 		virtual void setElementInformations(DiagramContext dc);
 
 		ElementData elementData() const;
@@ -222,6 +225,9 @@ class Element : public QetGraphicsItem
 		virtual void unlinkAllElements() {}
 		virtual void unlinkElement(Element *) {}
 		virtual void initLink(QETProject *);
+		QSet<QUuid> pendingLinks() const;
+		bool keepsSavedLinks() const {return !tmp_uuids_link.isEmpty();}
+		QList<std::pair<QUuid, int>> waitingLinks() const;
 			/**
 				Resolve tmp_uuids_link against a caller-supplied candidate
 				list instead of a project-wide search (bugtracker #607).
@@ -259,8 +265,8 @@ class Element : public QetGraphicsItem
 		 */
 		QString linkTypeToString() const;
 
-		void newUuid() {m_uuid = QUuid::createUuid();} 	//create new uuid for this element
-		void setUuid(const QUuid &uuid) {m_uuid = uuid;}
+		void newUuid() {setUuid(QUuid::createUuid());} 	//create new uuid for this element
+		void setUuid(const QUuid &uuid);
 
 	protected:
 		void drawAxes(QPainter *, const QStyleOptionGraphicsItem *);
@@ -329,6 +335,8 @@ class Element : public QetGraphicsItem
 
 	private:
 		void restoreSavedLinkOrder();
+		void storeInformation();
+		projectDataBase *placedStore() const;
 		bool m_must_highlight = false;
 		QSize   dimensions;
 		QPoint  hotspot_coord;

sources/qetgraphicsitem/terminal.cpp

@@ -1090,6 +1090,17 @@ QList<Terminal *> relatedPotentialTerminal (
 	// If terminal parent element is a folio report.
 	if (all_diagram && terminal -> parentElement() -> linkType() & Element::AllReport)
 	{
+			//The report's partner on a folio not built yet (QET_LAZY_FOLIOS)
+			//is built, so that a potential is followed as far as when every
+			//folio is; not while folios are being read or built, which
+			//would build whole report chains
+		Element *report = terminal->parentElement();
+		const QSet<QUuid> waiting = report->pendingLinks();
+		QETProject *project = report->diagram() ? report->diagram()->project() : nullptr;
+		if (!waiting.isEmpty() && project
+				&& project->state() != QETProject::ProjectParsingRunning) {
+			project->buildFoliosHoldingSymbols(waiting);
+		}
 		QList <Element *> elmt_list = terminal -> parentElement() -> linkedElements();
 		if (!elmt_list.isEmpty())
 		{

sources/qetproject.h

@@ -31,6 +31,7 @@
 #include "wirehops.h"
 #include "wiringrules.h"
 #include "diagram.h"
+#include "autoNum/assignvariables.h"
 #ifdef BUILD_WITHOUT_KF
 #	include "ui/nokde/kautosavefile.h"
 #else
@@ -44,6 +45,7 @@
 #include <QFuture>
 
 #include <array>
+#include <optional>
 
 class Diagram;
 class Element;
@@ -119,6 +121,22 @@ class QETProject : public QObject
 		QUuid derivedItemUuid(const QString &kind, const QString &key);
 		ProjectState state() const;
 		QList<Diagram *> diagrams() const;
+			//The folios whether their items are built or not
+			//(QET_LAZY_FOLIOS, LAZY-FOLIO-PLAN.md); diagrams() builds them
+		QList<Diagram *> folios() const;
+		bool deferringFolios() const {return m_deferring_folios;}
+		int unloadedFolioCount() const;
+		QList<Diagram *> builtFolios() const;
+		QList<Diagram *> cableLabelFolios();
+		QList<Diagram *> foliosWithWiresNotReconnected();
+		void buildFolioToShow(Diagram *folio);
+		void buildFoliosHolding(ElementData::Types kinds, bool free_only);
+		void buildFoliosHoldingSymbols(const QSet<QUuid> &symbols);
+		QSet<QUuid> symbolsOnUnbuiltFolios() const;
+		QSet<Diagram *> tableChainFolios(Diagram *folio) const;
+		void loadFolios() const;
+		void buildFolios(const QList<Diagram *> &folios) const;
+		void folioLoaded(Diagram *folio);
 		int folioIndex(const Diagram *) const;
 		XmlElementCollection *embeddedElementCollection()const;
 		TitleBlockTemplatesProjectCollection *embeddedTitleBlockTemplatesCollection();
@@ -240,6 +258,18 @@ class QETProject : public QObject
 										const QString &ignored_title = QString()) const;
 		static QString normalizedAutoNumName(const QString &name);
 		QVector<Element *> elementsUsingElementAutoNum(const QString &title) const;
+			/// A placed symbol's numbering, whether its folio is built or
+			/// not (QET_LAZY_FOLIOS): what is asked of every symbol of the
+			/// project when one is numbered
+		struct SymbolNumbering {
+			const Element *element = nullptr; ///< null on a folio not built
+			QString label;
+			QString formula;
+			QUuid scheme;   ///< the element numbering scheme it follows
+			autonum::sequentialNumbers sequence;
+			bool numbered = false; ///< neither a slave nor a report
+		};
+		QList<SymbolNumbering> symbolNumbering() const;
 
 		/**
 		 * @brief Renumber existing elements by element autonumbering scheme.
@@ -283,7 +313,8 @@ class QETProject : public QObject
 		void autoFolioNumberingNewFolios ();
 		void autoFolioNumberingSelectedFolios(int, int, const QString&);
 
-		QDomDocument toXml();
+		QDomDocument toXml(QHash<int, QByteArray> *kept_folios = nullptr);
+		static QString spliceKeptFolios(QString text, const QHash<int, QByteArray> &kept_folios);
 		bool close();
 		QETResult write();
 		bool isReadOnly() const;
@@ -293,6 +324,7 @@ class QETProject : public QObject
 		QString integrateTitleBlockTemplate(const TitleBlockTemplateLocation &, MoveTitleBlockTemplatesHandler *handler);
 		bool usesElement(const ElementsLocation &) const;
 		QList <ElementsLocation> unusedElements() const;
+		QList<ElementsLocation> unbuiltFolioElements() const;
 		bool usesTitleBlockTemplate(const TitleBlockTemplateLocation &);
 		bool projectWasModified();
 		bool projectOptionsWereModified();
@@ -474,6 +506,24 @@ class QETProject : public QObject
 			/// saved without an id (written before ids existed)
 		bool m_legacy_element_autonums = false;
 		void linkElementsToElementAutoNums();
+		void linkElementsToElementAutoNums(Diagram *folio);
+		QHash<QString, QStringList> elementAutoNumTitlesByFormula() const;
+		std::optional<QUuid> elementAutoNumIdToLink(
+				const DiagramContext &information,
+				const QHash<QString, QStringList> &titles_by_formula) const;
+		bool m_deferring_folios = false;
+			/// Saving may write a folio not built as it was read
+			/// (writesKeptFolios()): the file is this version's, its
+			/// database rows came from it, and nothing project-wide that
+			/// a folio's saved items depend on has changed since
+		bool m_kept_folios_trusted = false;
+		bool m_kept_folios_stale = false;
+			/// Something was edited since the project was opened: a table
+			/// filled from the database may have changed
+		bool m_edited_since_open = false;
+		void markKeptFoliosStale() {m_kept_folios_stale = true;}
+			/// The file being read, for each folio's text (readDiagramsXml())
+		QByteArray m_opened_content;
 		bool m_auto_conductor = true;
 		WireHops::Mode m_wire_hops = WireHops::Mode::None;
 			/// Texts drawn in a turned symbol stay horizontal (on for a new

sources/ui/diagrambgcolorbutton.cpp

@@ -150,8 +150,9 @@ void DiagramBgColorToolButton::applyColor(const QColor &color)
 	if (!editor) {
 		return;
 	}
+		//A folio not built yet takes the colour when it is drawn
 	for (ProjectView *pv : editor->openedProjects())
-		for (Diagram *d : pv->project()->diagrams())
+		for (Diagram *d : pv->project()->folios())
 			d->update();
 }
 
@@ -175,8 +176,9 @@ void DiagramBgColorToolButton::applySystemColor()
 	if (!editor) {
 		return;
 	}
+		//A folio not built yet takes the colour when it is drawn
 	for (ProjectView *pv : editor->openedProjects())
-		for (Diagram *d : pv->project()->diagrams())
+		for (Diagram *d : pv->project()->folios())
 			d->update();
 }
 

sources/ui/diagrameditorhandlersizewidget.cpp

@@ -60,7 +60,8 @@ void DiagramEditorHandlerSizeWidget::on_comboBox_currentIndexChanged(int index)
 	{
 		editor_->setProperty("graphics_handler_size", size);
 		for (auto project_view : editor_->openedProjects()) {
-			for (auto diagram : project_view->project()->diagrams()) {
+				//Handles exist on built folios only
+			for (auto diagram : project_view->project()->builtFolios()) {
 				for (const auto item : diagram->items()) {
 					if (item->type() == QetGraphicsHandlerItem::Type) {
 						auto handler = qgraphicsitem_cast<QetGraphicsHandlerItem *>(item);

sources/ui/jumptoelementdialog.cpp

@@ -169,7 +169,7 @@ void JumpToElementDialog::activateCurrentItem()
 	const int index = current->data(Qt::UserRole).toInt();
 	if (index == -1) {
 		const QList<Diagram *> diagrams = m_diagram->project()
-				? m_diagram->project()->diagrams()
+				? m_diagram->project()->folios()
 				: QList<Diagram *>();
 		const int folio = current->data(Qt::UserRole + 2).toInt();
 		if (folio >= 0 && folio < diagrams.size()) {
@@ -208,7 +208,8 @@ QListWidgetItem *JumpToElementDialog::cellItem(const QString &needle) const
 	if (!m_diagram || !m_diagram->project()) {
 		return nullptr;
 	}
-	const QList<Diagram *> diagrams = m_diagram->project()->diagrams();
+		//Folios' cells only (their border): folios() builds nothing
+	const QList<Diagram *> diagrams = m_diagram->project()->folios();
 
 	Diagram *diagram = m_diagram;
 	QString cell = needle;

tests/qttest/CMakeLists.txt

@@ -87,6 +87,13 @@ if(Python3_Interpreter_FOUND AND CMAKE_GENERATOR STREQUAL "Ninja")
       --source ${CMAKE_CURRENT_SOURCE_DIR}/attached_plain_paste_probe.cpp
       --fixture ${CMAKE_CURRENT_SOURCE_DIR}/fixtures/unlinked_contact_label.qet)
   set_tests_properties(tst_attachedplainpaste PROPERTIES TIMEOUT 300 RUN_SERIAL TRUE)
+  add_test(NAME tst_lazyfolios
+    COMMAND ${Python3_EXECUTABLE} ${CMAKE_CURRENT_SOURCE_DIR}/run_lazy_folios_probe.py
+      --build ${CMAKE_BINARY_DIR} --binary $<TARGET_FILE:qelectrotech>
+      --source ${CMAKE_CURRENT_SOURCE_DIR}/lazy_folios_probe.cpp
+      --fixture ${CMAKE_CURRENT_SOURCE_DIR}/../../examples/industrial.qet)
+  set_tests_properties(tst_lazyfolios PROPERTIES TIMEOUT 600 RUN_SERIAL TRUE
+    ENVIRONMENT "QT_QPA_PLATFORM=offscreen")
   # Deleting a cable, undoing the delete twice and then editing anything
   # has both cable commands tearing down the same cable. Runs under the
   # same objects the application uses, so a second free is caught.

tests/qttest/lazy_folios_probe.cpp

@@ -0,0 +1,579 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+// Lazy folios (QET_LAZY_FOLIOS, LAZY-FOLIO-PLAN.md stages 5.2 and 5.3),
+// linked against the application's objects: a folio shown in a project
+// opened without building its folios draws and links as in the project
+// opened as usual, building only it and the folios its links and tables
+// reach, and the project saves the same.
+#include <QApplication>
+#include <QFile>
+#include <QFontDatabase>
+#include <QImage>
+#include <QSqlRecord>
+#include <QSqlQuery>
+#include <QRegularExpression>
+#include <QPainter>
+#include <QSettings>
+#include <QTemporaryDir>
+#include <cstdio>
+#include <stdexcept>
+#include "../../sources/diagram.h"
+#include "../../sources/qetproject.h"
+#include "../../sources/qetresult.h"
+#include "../../sources/qetmessagebox.h"
+#include "../../sources/qetgraphicsitem/element.h"
+#include "../../sources/autoNum/elementautonumschemecommand.h"
+#include "../../sources/elementprovider.h"
+#include "../../sources/TerminalStrip/terminalstrip.h"
+#include "../../sources/ui/elementpropertieswidget.h"
+#include "../../sources/conductorautonumerotation.h"
+#include "../../sources/diagramcontent.h"
+#include "../../sources/diagramview.h"
+#include "../../sources/diagramevent/diagrameventaddpaste.h"
+#include <QKeyEvent>
+#include "../../sources/qetgraphicsitem/conductor.h"
+#include "../../sources/qetgraphicsitem/terminal.h"
+#include "../../sources/undocommand/changeelementinformationcommand.h"
+#include "../../sources/undocommand/changetitleblockcommand.h"
+#include "../../sources/undocommand/deleteqgraphicsitemcommand.h"
+#include "../../sources/factory/elementfactory.h"
+#include "../../sources/undocommand/addgraphicsobjectcommand.h"
+
+static void check(bool value, const char *message) { if (!value) throw std::runtime_error(message); }
+
+	//Every symbol's numbering, in a stable order
+static QStringList numbering(const QETProject &project)
+{
+	QStringList list;
+	for (const auto &symbol : project.symbolNumbering())
+		list << QStringList{symbol.label, symbol.formula, symbol.scheme.toString(),
+							symbol.sequence.unit.join(';'), symbol.sequence.ten.join(';'),
+							symbol.sequence.hundred.join(';'),
+							QString::number(symbol.numbered)}.join('|');
+	list.sort();
+	return list;
+}
+
+	//What the scheme @p title tells of the numbers its symbols carry
+static QString gaps(const QETProject &project, const QString &title)
+{
+	QStringList list;
+	for (const auto &gap : ElementAutoNumSchemeCommand::gapRanges(&project, title))
+		list << QString("%1-%2").arg(gap.from).arg(gap.to);
+	return list.join(',');
+}
+
+	//A symbol of @p location placed on folio @p i as the folio's editor
+	//places one (DiagramEventAddElement::addElement()), numbered with the
+	//scheme @p title: its label, and the numbers then free for it
+static QString place(QETProject &project, int i, const QString &location, const QString &title)
+{
+	Diagram *folio = project.folios().at(i);
+	project.buildFolioToShow(folio);
+	project.setCurrrentElementAutonum(title);
+	int state = 0;
+	Element *element = ElementFactory::Instance()->createElement(
+				ElementsLocation(location, &project), nullptr, &state);
+	check(!state, "symbol made");
+	element->setPos(QPointF(-500, -500));
+	folio->addItem(element);
+	auto *undo = new QUndoCommand("insert");
+	new AddGraphicsObjectCommand(element, folio, element->pos(), undo);
+	element->setUpFormula(true, undo);
+	folio->undoStack().push(undo);
+	element->freezeNewAddedElement();
+	QStringList free;
+	for (int n : ElementAutoNumSchemeCommand::freeNumbers(&project, title, element))
+		free << QString::number(n);
+	return element->actualLabel() + " free " + free.join(',');
+}
+
+	//The symbols a search of a project finds, by uuid
+static QStringList found(const QVector<QPointer<Element>> &elements)
+{
+	QStringList list;
+	for (const auto &element : elements)
+		list << element->uuid().toString();
+	list.sort();
+	return list;
+}
+
+	//Everyday edits on folio @p i, as its editor makes them: a symbol's
+	//information, a wire, the folio's title block, a linked symbol
+	//deleted, then one undo and one redo
+static void edit(QETProject &project, int i)
+{
+	Diagram *folio = project.folios().at(i);
+	project.buildFolioToShow(folio);
+	QList<Element *> elements = folio->elements();
+	std::sort(elements.begin(), elements.end(), [](Element *a, Element *b) {
+		return a->uuid() < b->uuid(); });
+	check(elements.size() > 2, "a folio with symbols to edit");
+
+	const DiagramContext old_info = elements.first()->elementInformations();
+	DiagramContext new_info = old_info;
+	new_info.addValue(QStringLiteral("comment"), QStringLiteral("edited lazily"));
+	folio->undoStack().push(new ChangeElementInformationCommand(elements.first(), old_info, new_info));
+
+	Terminal *ends[2] = {nullptr, nullptr};
+	for (Element *element : elements) {
+		for (Terminal *terminal : element->terminals()) {
+			if (terminal->conductors().isEmpty()
+					&& (!ends[0] || ends[0]->parentElement() != element)) {
+				ends[ends[0] ? 1 : 0] = terminal;
+				break;
+			}
+		}
+		if (ends[1]) break;
+	}
+	if (ends[1]) {
+		auto *undo = new QUndoCommand(QStringLiteral("wire"));
+		auto *wire = new Conductor(ends[0], ends[1]);
+		new AddGraphicsObjectCommand(wire, folio, QPointF(), undo);
+		ConductorAutoNumerotation numbering(wire, folio, undo);
+		numbering.numerate();
+		folio->undoStack().push(undo);
+	}
+
+	const TitleBlockProperties old_block = folio->border_and_titleblock.exportTitleBlock();
+	TitleBlockProperties new_block = old_block;
+	new_block.title += QStringLiteral(" (edited)");
+	folio->undoStack().push(new ChangeTitleBlockCommand(folio, old_block, new_block));
+
+		//Copy three symbols and paste them, as Ctrl+C then Ctrl+Shift+V
+		//and Return do
+	{
+		DiagramView view(folio);
+		folio->clearSelection();
+		for (int n = 0 ; n < 3 ; ++n)
+			elements.at(n)->setSelected(true);
+		view.copy();
+		auto *paste = new DiagramEventAddPaste(folio, QPointF(), DiagramEventAddPaste::AtOrigin);
+		folio->setEventInterface(paste);
+		QKeyEvent drop(QEvent::KeyPress, Qt::Key_Return, Qt::NoModifier);
+		paste->keyPressEvent(&drop);
+		folio->clearEventInterface();
+	}
+
+	Element *linked = nullptr;
+	for (Element *element : elements)
+		if (!element->linkedElements().isEmpty()) { linked = element; break; }
+	folio->clearSelection();
+	(linked ? linked : elements.last())->setSelected(true);
+	folio->undoStack().push(new DeleteQGraphicsItemCommand(folio, DiagramContent(folio, true)));
+
+	project.undoStack()->undo();
+	project.undoStack()->redo();
+}
+
+	//The project as saving writes it: folios not built written as read
+	//when building them would write the same (QETProject::toXml())
+static QString saved(QETProject &project)
+{
+	QHash<int, QByteArray> kept;
+	const QDomDocument document = project.toXml(&kept);
+	return QETProject::spliceKeptFolios(document.toString(4), kept);
+}
+
+	//The rows of the project database's tables, in their order, read as
+	//every caller reads them (newQuery(): brought up to date first)
+static QStringList tables(QETProject &project)
+{
+	QStringList rows;
+	for (const char *table : {"diagram", "diagram_info", "element", "element_info",
+							  "terminal", "conductor", "link"}) {
+		QSqlQuery query = project.dataBase()->newQuery(
+					QStringLiteral("SELECT * FROM %1 ORDER BY rowid").arg(QLatin1String(table)));
+		check(query.exec(), "a table read");
+		QStringList table_rows;
+		while (query.next()) {
+			QStringList row;
+			for (int i = 0 ; i < query.record().count() ; ++i)
+				row << query.value(i).toString();
+			table_rows << QLatin1String(table) + ": " + row.join('|');
+		}
+			//Rows are written in the order the scene gives a folio's items,
+			//which is not the same from one opening to the next: two usual
+			//opens given the same edits differ in it (637 rows of 3 394 on
+			//industrial.qet). What a table holds is compared, not its order
+		table_rows.sort();
+		rows << table_rows;
+	}
+	return rows;
+}
+
+static QImage render(Diagram *folio)
+{
+	const QRectF rect = folio->border_and_titleblock.borderAndTitleBlockRect().adjusted(-5, -5, 5, 5);
+	QImage image(rect.size().toSize(), QImage::Format_RGB32);
+	image.fill(Qt::white);
+	QPainter painter(&image);
+	folio->render(&painter, QRectF(QPointF(0, 0), rect.size()), rect);
+	return image;
+}
+
+	//Each symbol's partners, in their order
+static QStringList links(Diagram *folio)
+{
+	QStringList list;
+	for (Element *element : folio->elements()) {
+		QStringList partners;
+		for (Element *partner : element->linkedElements())
+			partners << partner->uuid().toString();
+		list << element->uuid().toString() + ' ' + partners.join(',');
+	}
+	list.sort();
+	return list;
+}
+
+int main(int argc, char **argv)
+{
+	QApplication app(argc, argv); std::freopen(argv[2], "w", stdout);
+	QTemporaryDir settings; QSettings::setDefaultFormat(QSettings::IniFormat);
+	QSettings::setPath(QSettings::IniFormat, QSettings::UserScope, settings.path());
+	QCoreApplication::setOrganizationName("QETLazyFoliosRegression");
+	QETProject::setBackupEnabled(false); QET::QetMessageBox::setNonInteractive(true);
+	QFontDatabase::addApplicationFont(":/fonts/LiberationSans-Regular.ttf");
+		//Folios not built saved as read (QETProject::toXml()): this
+		//fixture is written by this version's own save
+	qputenv("QET_LAZY_SAVE_KEPT", "1");
+	try {
+		const QString output = QString::fromLocal8Bit(argv[3]);
+		qunsetenv("QET_LAZY_FOLIOS");
+			//A file saved by this version: its folios carry their uuids,
+			//which opening without building them needs
+		const QString path = output + "/lazy_folios.qet";
+		QSet<int> strip_folios;
+		{
+			QETProject source(QString::fromLocal8Bit(argv[1]));
+			check(source.state() == QETProject::Ok, "fixture opens");
+				//A terminal strip of terminals on several folios: it is
+				//read with the project, before any folio is built
+			TerminalStrip *strip = source.newTerminalStrip(QStringLiteral("=A1"), QStringLiteral("+B1"),
+														  QStringLiteral("X99"));
+			int added = 0;
+			for (Diagram *folio : source.folios())
+				for (Element *element : folio->elements())
+					if (element->elementData().m_type == ElementData::Terminal && added < 12
+							&& strip->addTerminal(element)) {
+						++added;
+						strip_folios.insert(source.folioIndex(folio));
+					}
+			check(added > 3, "a terminal strip with terminals");
+			source.setFilePath(path);
+			check(source.write().isOk(), "fixture saved by this version");
+		}
+		QETProject eager(path);
+		check(eager.state() == QETProject::Ok, "project opens");
+		{
+			qputenv("QET_LAZY_FOLIOS", "1");
+			QETProject lazy_strips(path);
+			qunsetenv("QET_LAZY_FOLIOS");
+			auto strip_of = [](const QETProject &project) {
+				for (TerminalStrip *strip : project.terminalStrip())
+					if (strip->name() == QStringLiteral("X99")) return strip->physicalTerminalCount();
+				return -1;
+			};
+			check(strip_of(lazy_strips) > 3 && strip_of(lazy_strips) == strip_of(eager),
+				  "a terminal strip keeps its terminals when the folios are not built");
+		}
+		const QList<Diagram *> folios = eager.folios();
+		check(folios.size() > 3, "several folios");
+		QList<QImage> images; QList<QStringList> partners;
+		int linked = 0;
+		for (Diagram *folio : folios) {
+			images << render(folio);
+			partners << links(folio);
+			for (Element *element : folio->elements())
+				linked += !element->linkedElements().isEmpty();
+		}
+		check(linked > 0, "the project has linked symbols");
+
+		qputenv("QET_LAZY_FOLIOS", "1");
+		auto same = [&](QETProject &lazy, int i, const char *what) {
+			Diagram *folio = lazy.folios().at(i);
+			lazy.buildFolioToShow(folio);
+			if (render(folio) != images.at(i) || links(folio) != partners.at(i)) {
+				std::printf("folio %d, %s: differs\n", i + 1, what);
+				throw std::runtime_error("a folio shown lazily draws or links as opened as usual");
+			}
+		};
+			//Each folio first after opening
+		for (int i = 0; i < folios.size(); ++i) {
+			QETProject lazy(path);
+			check(lazy.unloadedFolioCount() == folios.size() - strip_folios.size(),
+				  "opened building only the folios of the terminal strip's terminals");
+			same(lazy, i, "shown first");
+			check(lazy.unloadedFolioCount() > 0, "showing a folio does not build them all");
+		}
+			//Every folio, one after the other, then the save
+		QETProject lazy(path);
+		for (int i = 0; i < folios.size(); ++i)
+			same(lazy, i, "shown in turn");
+		check(lazy.toXml().toString() == eager.toXml().toString(), "saves as opened as usual");
+		check(lazy.undoStack()->isClean(), "showing folios changes nothing");
+
+			//Numbering asks every symbol of the project: it is answered for
+			//the folios not built without building them, as when built
+		QETProject numbered(path);
+		check(numbering(numbered) == numbering(eager), "symbols' numbering as when built");
+		const QStringList titles = eager.elementAutoNum().keys();
+		check(!titles.isEmpty(), "the project has element numbering schemes");
+		for (const QString &title : titles)
+			check(gaps(numbered, title) == gaps(eager, title), "a scheme's gaps as when built");
+		check(numbered.unloadedFolioCount() == folios.size() - strip_folios.size(), "numbering read without building");
+			//A symbol placed on a folio, numbered by a scheme others follow
+		QString location, title;
+		int folio = -1;
+		for (const auto &symbol : eager.symbolNumbering()) {
+			if (symbol.numbered && symbol.element && !eager.elementAutoNumTitle(symbol.scheme).isEmpty()) {
+				location = symbol.element->location().toString();
+				title = eager.elementAutoNumTitle(symbol.scheme);
+				folio = eager.folios().indexOf(symbol.element->diagram());
+				break;
+			}
+		}
+		check(folio >= 0, "a symbol following a scheme");
+		const QString placed = place(numbered, folio, location, title);
+		std::printf("placed on folio %d with %s: %s\n", folio + 1, qPrintable(title), qPrintable(placed));
+		check(numbered.unloadedFolioCount() > 0, "numbering a placed symbol does not build every folio");
+		QETProject usual(path);
+		check(placed == place(usual, folio, location, title), "a placed symbol numbered as when built");
+			//The candidates a link tab lists (ElementProvider): found as
+			//when built, building only the folios which hold some
+		const ElementProvider usual_search(&eager);
+		for (const ElementData::Types kinds : {ElementData::Types(ElementData::Slave),
+											   ElementData::Types(ElementData::Master),
+											   ElementData::Types(ElementData::AllReport),
+											   ElementData::Types(ElementData::Terminal)}) {
+			QETProject searched(path);
+			const ElementProvider search(&searched);
+			const QStringList lazy_free = found(search.freeElement(kinds)), usual_free = found(usual_search.freeElement(kinds));
+			if (lazy_free != usual_free) {
+				for (const QString &u : usual_free) if (!lazy_free.contains(u)) std::printf("  only when built: %s\n", qPrintable(u));
+				for (const QString &u : lazy_free) if (!usual_free.contains(u)) std::printf("  only lazily: %s\n", qPrintable(u));
+			}
+			check(lazy_free == usual_free, "free symbols found as when built");
+			std::printf("free symbols of kinds %d: %d folios built\n", int(kinds),
+						int(folios.size() - searched.unloadedFolioCount()));
+			check(found(search.find(kinds)) == found(usual_search.find(kinds)),
+				  "symbols found as when built");
+		}
+		{
+			QETProject searched(path);
+			ElementProvider(&searched).freeElement(ElementData::Slave);
+			check(searched.unloadedFolioCount() > 0, "a search for free contacts does not build every folio");
+		}
+			//Selecting a symbol shows its properties, a link tab for a
+			//coil, a contact or a report: the folio and few others built
+		for (const Element::kind kind : {Element::Master, Element::Slave, Element::NextReport,
+										 Element::PreviousReport}) {
+			QETProject selected(path);
+			Element *element = nullptr;
+			for (int i = 0 ; !element && i < folios.size() ; ++i) {
+				for (Element *candidate : eager.folios().at(i)->elements()) {
+					if (candidate->linkType() == kind) {
+						selected.buildFolioToShow(selected.folios().at(i));
+						for (Element *e : selected.folios().at(i)->elements())
+							if (e->uuid() == candidate->uuid()) element = e;
+						break;
+					}
+				}
+			}
+			check(element, "a symbol of each kind with a link tab");
+			const int before = selected.unloadedFolioCount();
+			delete new ElementPropertiesWidget(element);
+			std::printf("properties of a symbol of kind %d: %d more folios built, %d not built\n",
+						int(kind), before - selected.unloadedFolioCount(), selected.unloadedFolioCount());
+			check(selected.unloadedFolioCount() > 0, "selecting a symbol does not build every folio");
+		}
+			//Everyday edits on a folio linked to others: the others stay
+			//not built, and the project saves as when they are
+		int busiest = 0, most = -1;
+		for (int i = 0 ; i < folios.size() ; ++i) {
+			int partners = 0;
+			for (Element *element : folios.at(i)->elements())
+				for (Element *partner : element->linkedElements())
+					partners += partner->diagram() != folios.at(i);
+			if (partners > most) { most = partners; busiest = i; }
+		}
+		{
+			QETProject edited(path), usual(path);
+			qunsetenv("QET_LAZY_FOLIOS");
+			QETProject usual_edited(path);
+			qputenv("QET_LAZY_FOLIOS", "1");
+			edit(edited, busiest);
+			std::printf("edits on folio %d (%d links to other folios): %d folios not built\n",
+						busiest + 1, most, edited.unloadedFolioCount());
+			check(edited.unloadedFolioCount() > 0, "editing a folio does not build every folio");
+			edit(usual_edited, busiest);
+				//Made by the edits, a new wire's uuid is random: any uuid the
+				//file had not is "new" before comparing
+			QFile saved(path); saved.open(QIODevice::ReadOnly);
+			const QString before = QString::fromUtf8(saved.readAll());
+			static const QRegularExpression uuid_re(QStringLiteral("uuid=\"(\\{[0-9a-f-]{36}\\})\""));
+			auto known = [&before](QString xml) {
+				QString out;
+				qsizetype at = 0;
+				for (auto it = uuid_re.globalMatch(xml) ; it.hasNext() ; ) {
+					const auto match = it.next();
+					out += xml.mid(at, match.capturedStart() - at);
+					out += before.contains(match.captured(1)) ? match.captured(0)
+															  : QStringLiteral("uuid=\"new\"");
+					at = match.capturedEnd();
+				}
+				return out + xml.mid(at);
+			};
+			const QStringList lazy_rows = tables(edited), usual_rows = tables(usual_edited);
+			static const QRegularExpression bare_uuid_re(QStringLiteral("\\{[0-9a-f-]{36}\\}"));
+			auto known_row = [&before](QString row) {
+				for (auto it = bare_uuid_re.globalMatch(QString(row)) ; it.hasNext() ; ) {
+					const QString uuid = it.next().captured(0);
+					if (!before.contains(uuid)) row.replace(uuid, QStringLiteral("new"));
+				}
+				return row;
+			};
+			check(edited.unloadedFolioCount() > 0, "reading the database does not build every folio");
+			QStringList lazy_known, usual_known;
+			for (const QString &row : lazy_rows) lazy_known << known_row(row);
+			for (const QString &row : usual_rows) usual_known << known_row(row);
+			lazy_known.sort();
+			usual_known.sort();
+			int differing = 0;
+			for (int i = 0 ; i < std::max(lazy_known.size(), usual_known.size()) ; ++i)
+				if (lazy_known.value(i) != usual_known.value(i) && differing++ < 5)
+					std::printf("  row %d: lazy  %s\n         usual %s\n", i, qPrintable(lazy_known.value(i).left(160)),
+								qPrintable(usual_known.value(i).left(160)));
+			std::printf("database after the edits: %d rows, %d differ\n", int(usual_rows.size()), differing);
+			check(!differing, "the database after the edits as when every folio is built");
+				//A pasted copy has a random uuid, and a folio's symbols are
+				//saved in uuid order: the lines are compared, not their order
+			auto lines = [&known](const QString &xml) {
+				QStringList list = known(xml).split(QLatin1Char('\n'));
+				list.sort();
+				return list.join(QLatin1Char('\n'));
+			};
+			const QString a = lines(edited.toXml().toString()), b = lines(usual_edited.toXml().toString());
+			if (a != b) {
+				QFile fa(output + "/edited-lazy.xml"); fa.open(QIODevice::WriteOnly); fa.write(a.toUtf8());
+				QFile fb(output + "/edited-usual.xml"); fb.open(QIODevice::WriteOnly); fb.write(b.toUtf8());
+			}
+			check(a == b,
+				  "edits save as when every folio is built");
+		}
+			//Saving writes the folios not built as they were read, the same
+			//bytes as building them would write
+		const QString usual_text = saved(eager);
+		{
+			QETProject untouched(path);
+			const int unbuilt = untouched.unloadedFolioCount();
+			const QString untouched_text = saved(untouched);
+			if (untouched_text != usual_text) {
+				QFile fa(output + "/untouched-lazy.xml"); fa.open(QIODevice::WriteOnly); fa.write(untouched_text.toUtf8());
+				QFile fb(output + "/untouched-usual.xml"); fb.open(QIODevice::WriteOnly); fb.write(usual_text.toUtf8());
+			}
+			check(untouched_text == usual_text, "a project saved without building, as when built");
+				//Only the partners of the folios the terminal strip built
+			std::printf("saved untouched: %d of %d folios not built built to save\n",
+						unbuilt - untouched.unloadedFolioCount(), unbuilt);
+			check(untouched.unloadedFolioCount() > 0, "saving does not build every folio");
+		}
+			//After everyday edits on a folio: as when built, others not built
+		{
+			QETProject edited(path), usual(path);
+			qunsetenv("QET_LAZY_FOLIOS");
+			QETProject usual_edited(path);
+			qputenv("QET_LAZY_FOLIOS", "1");
+			edit(edited, busiest);
+			edit(usual_edited, busiest);
+			QFile file(path); file.open(QIODevice::ReadOnly);
+			const QString before = QString::fromUtf8(file.readAll());
+			static const QRegularExpression uuid_re(QStringLiteral("\\{[0-9a-f-]{36}\\}"));
+			auto lines = [&before](QString text) {
+				for (auto it = uuid_re.globalMatch(QString(text)) ; it.hasNext() ; ) {
+					const QString uuid = it.next().captured(0);
+					if (!before.contains(uuid)) text.replace(uuid, QStringLiteral("new"));
+				}
+				QStringList list = text.split(QLatin1Char('\n'));
+				list.sort();
+				return list;
+			};
+			const QStringList la = lines(saved(edited)), lb = lines(saved(usual_edited));
+			if (la != lb) {
+				int shown = 0;
+				for (const QString &l : lb) if (!la.contains(l) && shown++ < 6) std::printf("  only usual: %s\n", qPrintable(l.trimmed().left(150)));
+				shown = 0;
+				for (const QString &l : la) if (!lb.contains(l) && shown++ < 6) std::printf("  only lazy:  %s\n", qPrintable(l.trimmed().left(150)));
+			}
+			check(la == lb, "edits saved without building, as when built");
+			std::printf("saved after the edits: %d folios not built\n", edited.unloadedFolioCount());
+			check(edited.unloadedFolioCount() > 0, "saving after edits does not build every folio");
+		}
+			//A folio not built given a new title: it and the folios its
+			//links reach are built to be saved, the others not
+		{
+			QETProject renamed(path);
+			qunsetenv("QET_LAZY_FOLIOS");
+			QETProject usual_renamed(path);
+			qputenv("QET_LAZY_FOLIOS", "1");
+			for (QETProject *project : {&renamed, &usual_renamed}) {
+				Diagram *folio = project->folios().at(busiest);
+				TitleBlockProperties block = folio->border_and_titleblock.exportTitleBlock();
+				block.title += QStringLiteral(" (renamed)");
+				folio->border_and_titleblock.importTitleBlock(block);
+			}
+			check(saved(renamed) == saved(usual_renamed), "a renamed folio saved as when built");
+			std::printf("saved after a folio not built was renamed: %d folios not built\n", renamed.unloadedFolioCount());
+			check(renamed.unloadedFolioCount() > 0, "renaming a folio does not build every folio to save");
+		}
+			//Project properties, which any folio's texts can use: every
+			//folio is built to be saved
+		{
+			QETProject changed(path);
+			qunsetenv("QET_LAZY_FOLIOS");
+			QETProject usual_changed(path);
+			qputenv("QET_LAZY_FOLIOS", "1");
+			for (QETProject *project : {&changed, &usual_changed}) {
+				DiagramContext properties = project->projectProperties();
+				properties.addValue(QStringLiteral("lazy_test"), QStringLiteral("1"));
+				project->setProjectProperties(properties);
+			}
+			check(saved(changed) == saved(usual_changed), "changed project properties saved as when built");
+			check(changed.unloadedFolioCount() == 0, "changed project properties build every folio to save");
+		}
+			//A potential through folio reports is followed as far as when
+			//every folio is built
+		{
+			Conductor *usual_wire = nullptr;
+			for (Diagram *folio : eager.folios())
+				for (Element *element : folio->elements())
+					if ((element->linkType() & Element::AllReport) && !element->conductors().isEmpty()
+							&& !usual_wire)
+						usual_wire = element->conductors().first();
+			check(usual_wire, "a wire on a folio report");
+			auto potential = [](Conductor *wire) {
+				QStringList list;
+				for (Conductor *c : wire->relatedPotentialConductors(true))
+					list << c->uuid().toString();
+				list.sort();
+				return list;
+			};
+			QETProject followed(path);
+			Diagram *folio = followed.folios().at(eager.folioIndex(usual_wire->diagram()));
+			followed.buildFolioToShow(folio);
+			Conductor *wire = nullptr;
+			for (Conductor *c : folio->conductors())
+				if (c->uuid() == usual_wire->uuid()) wire = c;
+			check(wire, "the same wire");
+			check(potential(wire) == potential(usual_wire), "a potential followed as when built");
+			std::printf("potential through reports: %d wires, %d folios not built\n",
+						int(potential(wire).size()), followed.unloadedFolioCount());
+		}
+		std::printf("PASS: %d folios\n", int(folios.size()));
+	} catch (const std::exception &error) {
+		std::printf("FAIL: %s\n", error.what());
+		std::fflush(stdout);
+		return 1;
+	}
+	std::fflush(stdout);
+	return 0;
+}

tests/qttest/run_lazy_folios_probe.py

@@ -0,0 +1,60 @@
+#!/usr/bin/env python3
+"""Link the lazy folios integration probe using an existing Ninja app build.
+
+Reuses app objects without duplicating the app or introducing a core-library
+refactor. No application source or existing executable is replaced. The
+generated manifest, probe binary, reports and export fixtures stay in build/.
+"""
+import argparse
+import pathlib
+import re
+import shutil
+import subprocess
+import sys
+
+parser = argparse.ArgumentParser()
+parser.add_argument('--build', required=True)
+parser.add_argument('--binary', required=True)
+parser.add_argument('--source', required=True)
+parser.add_argument('--fixture', required=True)
+args = parser.parse_args()
+build = pathlib.Path(args.build).resolve()
+binary = pathlib.Path(args.binary).resolve()
+source = pathlib.Path(args.source).resolve()
+fixture = pathlib.Path(args.fixture).resolve()
+manifest = (build / 'build.ninja').read_text(encoding='utf-8')
+match = re.search(r'^build (\S*?/sources/main\.cpp\.(?:obj|o)):', manifest, re.MULTILINE)
+if not match:
+    sys.exit('Cannot find the application main object in the Ninja build.')
+main_object = match.group(1)
+probe_object = main_object.replace('main.cpp.', 'lazy_folios_probe.cpp.')
+probe_binary = binary.with_name('lazy_folios_probe' + binary.suffix)
+def escape(path):
+    return pathlib.Path(path).as_posix().replace('$', '$$').replace(':', '$:').replace(' ', '$ ')
+main_source = source.parents[2] / 'sources' / 'main.cpp'
+manifest = manifest.replace(main_object, probe_object)
+manifest = manifest.replace(escape(main_source), escape(source))
+if binary.suffix:
+    manifest = manifest.replace(binary.name, probe_binary.name)
+else:
+    old_target = escape(binary.name if binary.parent == build else binary)
+    new_target = escape(probe_binary.name if probe_binary.parent == build else probe_binary)
+    manifest = manifest.replace('build ' + old_target + ':', 'build ' + new_target + ':')
+    old_file = binary.name if binary.parent == build else binary.as_posix()
+    new_file = probe_binary.name if probe_binary.parent == build else probe_binary.as_posix()
+    manifest = re.sub(r'^  TARGET_FILE = ' + re.escape(old_file) + r'$',
+                      '  TARGET_FILE = ' + new_file, manifest, flags=re.MULTILINE)
+probe_manifest = build / 'lazy-folios-probe.ninja'
+probe_manifest.write_text(manifest, encoding='utf-8')
+ninja = shutil.which('ninja')
+if not ninja:
+    sys.exit('Ninja is required for the integration probe.')
+target = probe_binary.name if probe_binary.parent == build else str(probe_binary)
+subprocess.run([ninja, '-C', str(build), '-f', probe_manifest.name, target], check=True)
+output = build / 'lazy-folios'
+output.mkdir(exist_ok=True)
+report = output / 'results.txt'
+result = subprocess.run([str(probe_binary), str(fixture), str(report), str(output)], timeout=500)
+if report.exists():
+    print(report.read_text(encoding='utf-8', errors='replace'))
+sys.exit(result.returncode)

tests/qttest/tst_resaveunchanged.cpp

@@ -317,6 +317,169 @@ private slots:
 		QCOMPARE(without_save_stamps(read(back)), without_save_stamps(read(straight)));
 	}
 
+	// QElectroTech run in a sandbox of its own with @p args, the store
+	// check on (QET_CHECK_ELEMENT_INFO_STORE); its output
+	QString runChecked(const QStringList &args, bool eager = false)
+	{
+		const QString home = m_dir.filePath(QStringLiteral("home%1").arg(m_run++));
+		QDir().mkpath(home);
+		QProcessEnvironment env = QProcessEnvironment::systemEnvironment();
+		env.insert(QStringLiteral("QT_QPA_PLATFORM"), QStringLiteral("offscreen"));
+		env.insert(QStringLiteral("QET_ENABLE_SCRIPTING"), QStringLiteral("1"));
+		env.insert(QStringLiteral("QET_CHECK_ELEMENT_INFO_STORE"), QStringLiteral("1"));
+		if (eager) {
+			env.remove(QStringLiteral("QET_LAZY_FOLIOS")); //every folio built on opening
+		}
+		env.insert(QStringLiteral("HOME"), home);
+		env.insert(QStringLiteral("XDG_CONFIG_HOME"), home + QStringLiteral("/config"));
+		env.insert(QStringLiteral("XDG_DATA_HOME"), home + QStringLiteral("/data"));
+		QProcess proc;
+		proc.setProcessEnvironment(env);
+		proc.start(QStringLiteral(QET_TEST_BINARY_PATH), args);
+		if (!proc.waitForFinished(180000)) return {};
+		return QString::fromUtf8(proc.readAllStandardOutput() + proc.readAllStandardError());
+	}
+
+	// The stores of symbol information and folio title blocks
+	// (DB-ACCESSORS-PLAN.md stages 4.1, 4.4) agree with every placed symbol
+	// and folio once a project is open: every example.
+	void elementInfoStoreAgrees_data()
+	{
+		QTest::addColumn<QString>("project");
+		const QDir examples(QStringLiteral(QET_EXAMPLES_DIR));
+		for (const QString &f : examples.entryList({QStringLiteral("*.qet")}, QDir::Files, QDir::Name))
+			QTest::newRow(f.toUtf8().constData()) << examples.filePath(f);
+	}
+	void elementInfoStoreAgrees()
+	{
+		QFETCH(QString, project);
+		const QString out = runChecked({QStringLiteral("--resave"), project,
+										m_dir.filePath(QStringLiteral("store%1.qet").arg(m_run))});
+		QVERIFY2(out.contains(QStringLiteral("element information store: 0 differ")), qPrintable(out.right(600)));
+		QVERIFY2(out.contains(QStringLiteral("folio title block store: 0 differ")), qPrintable(out.right(600)));
+		QVERIFY2(out.contains(QStringLiteral("wire properties store: 0 differ")), qPrintable(out.right(600)));
+	}
+
+	// The stores filled from the document before the folios are built
+	// (DB-ACCESSORS-PLAN.md stage 4.6) hold what building them gives, for a
+	// project saved by this version (every symbol, folio and wire carries
+	// a uuid): nothing differs, nothing is left unplaced.
+	void storesFilledBeforeBuilding()
+	{
+		const QString saved = resave(QStringLiteral(QET_EXAMPLES_DIR "/industrial.qet"));
+		QVERIFY2(!saved.isEmpty(), "--resave failed");
+		const QString out = runChecked({QStringLiteral("--resave"), saved,
+										m_dir.filePath(QStringLiteral("prefilled.qet"))}, true);
+		const QRegularExpression line(QStringLiteral(
+				"filled before building: symbols (\\d+) agree, 0 differ, 0 not placed; "
+				"folios (\\d+) agree, 0 differ, 0 not placed; wires (\\d+) agree, 0 differ, 0 not placed"));
+		const QRegularExpressionMatch m = line.match(out);
+		QVERIFY2(m.hasMatch(), qPrintable(out.right(600)));
+		QVERIFY(m.captured(1).toInt() > 600 && m.captured(2).toInt() == 50 && m.captured(3).toInt() > 600);
+	}
+
+	// Title block fields stamped on every folio go through the store, and
+	// the saved folios carry them (a folio saves what the store holds).
+	void folioTitleBlockStoreAfterSetTitleBlock()
+	{
+		const QString saved = m_dir.filePath(QStringLiteral("stamped.qet"));
+		const QString out = runChecked({QStringLiteral("--set-titleblock"),
+										QStringLiteral(QET_EXAMPLES_DIR "/industrial.qet"), saved,
+										QStringLiteral("author=Ann"), QStringLiteral("extrafield=Hello")});
+		QVERIFY2(out.contains(QStringLiteral("folio title block store: 0 differ")), qPrintable(out.right(600)));
+		const QByteArray xml = read(saved);
+		QCOMPARE(xml.count("<diagram "), xml.count("author=\"Ann\"") - 1);
+		QCOMPARE(xml.count("<diagram "), xml.count("name=\"extrafield\"") - 1);
+	}
+
+	// ... and after a copy of a symbol, which briefly shares its original's
+	// uuid, and an undo: the original kept no row once (duplicateElements
+	// is the copy the paste and folio duplication make).
+	void elementInfoStoreAfterCopyAndUndo()
+	{
+#ifndef QET_HAS_SCRIPTING
+		QSKIP("needs --run: this QElectroTech is built without Qt Qml");
+#endif
+		const QString script = m_dir.filePath(QStringLiteral("copy.js"));
+		QFile js(script);
+		QVERIFY(js.open(QIODevice::WriteOnly));
+		js.write(QStringLiteral(
+				 "var f = 0; while (qet.elementUuids(f).length < 3) ++f;\n"
+				 "var e = qet.elementUuids(f);\n"
+				 "qet.log('COPY ' + qet.duplicateElements(f, [e[0], e[1]], f, 300, 300).length);\n"
+				 "qet.log('DELETE ' + qet.deleteElement(f, e[2]) + ' UNDO ' + qet.undo());\n"
+				 "qet.log('SAVED ' + qet.save('%1'));\n").arg(m_dir.filePath(QStringLiteral("copied.qet"))).toUtf8());
+		js.close();
+		const QString out = runChecked({QStringLiteral("--run"), script,
+										QStringLiteral(QET_EXAMPLES_DIR "/industrial.qet")});
+		QVERIFY2(out.contains(QStringLiteral("COPY 2")) && out.contains(QStringLiteral("UNDO true"))
+				 && out.contains(QStringLiteral("SAVED true")), qPrintable(out.right(600)));
+		QVERIFY2(out.contains(QStringLiteral("element information store: 0 differ")), qPrintable(out.right(600)));
+	}
+
+	// After copies of linked symbols, of wired symbols, and the undo of a
+	// folio's removal, the project database's symbol, link, wire and
+	// terminal rows are those a fresh open of the saved project builds
+	// (F106, F107): a copy is placed while it still carries its original's
+	// uuid, and an undone folio removal put back its symbols but not their
+	// rows.
+	void symbolRowsAfterCopyAndFolioUndo()
+	{
+#ifndef QET_HAS_SCRIPTING
+		QSKIP("needs --run: this QElectroTech is built without Qt Qml");
+#endif
+		const QString rows = QStringLiteral(
+				 "function rows() { return JSON.stringify(["
+				 "qet.query('SELECT uuid, diagram_uuid, type FROM element ORDER BY uuid'),"
+				 "qet.query('SELECT element_uuid, label, comment FROM element_info ORDER BY element_uuid'),"
+				 "qet.query('SELECT element_uuid, linked_uuid FROM link ORDER BY element_uuid, linked_uuid'),"
+				 "qet.query('SELECT uuid, terminal1_element_uuid, terminal2_element_uuid, text FROM conductor ORDER BY uuid'),"
+				 "qet.query('SELECT uuid, element_uuid FROM terminal ORDER BY uuid, element_uuid')]); }\n");
+		const QString edit = m_dir.filePath(QStringLiteral("rows_edit.js")),
+				dump = m_dir.filePath(QStringLiteral("rows_dump.js")),
+				saved = m_dir.filePath(QStringLiteral("rows.qet"));
+		QFile js(edit);
+		QVERIFY(js.open(QIODevice::WriteOnly));
+		js.write((rows + QStringLiteral(
+				 "var linked = -1;\n"
+				 "for (var f = 0; f < qet.folioCount() && linked < 0; ++f)\n"
+				 "  qet.elementUuids(f).forEach(function (u) { if (qet.linkedElements(f, u).length) linked = f; });\n"
+				 "qet.log('UNDONE ' + (qet.removeFolio(linked) && qet.undo()));\n"
+				 "var copied = 0;\n"
+				 "for (var f = 0; f < qet.folioCount() && copied < 3; ++f) {\n"
+				 "  var e = qet.elementUuids(f);\n"
+				 "  for (var i = 0; i < e.length && copied < 3; ++i)\n"
+				 "    if (qet.linkedElements(f, e[i]).length)\n"
+				 "      copied += qet.duplicateElements(f, [e[i]], f, 300, 300).length;\n"
+				 "}\n"
+				 "qet.log('COPIED ' + copied);\n"
+				 "var wf = 0; while (qet.elementUuids(wf).length < 6) ++wf;\n"
+				 "var wires = qet.conductorCount(wf), w = qet.elementUuids(wf);\n"
+				 "qet.log('WIRED ' + qet.duplicateElements(wf, w.slice(0, 6), wf, 300, 300).length"
+				 " + (qet.conductorCount(wf) > wires ? ' with wires' : ''));\n"
+				 "qet.log('ROWS ' + rows());\n"
+				 "qet.log('SAVED ' + qet.save('%1'));\n").arg(saved)).toUtf8());
+		js.close();
+		QFile js2(dump);
+		QVERIFY(js2.open(QIODevice::WriteOnly));
+		js2.write((rows + QStringLiteral("qet.log('ROWS ' + rows());\n")).toUtf8());
+		js2.close();
+
+		const QString edited = runChecked({QStringLiteral("--run"), edit,
+										   QStringLiteral(QET_EXAMPLES_DIR "/industrial.qet")});
+		QVERIFY2(edited.contains(QStringLiteral("COPIED 3")) && edited.contains(QStringLiteral("WIRED 6 with wires"))
+				 && edited.contains(QStringLiteral("UNDONE true"))
+				 && edited.contains(QStringLiteral("SAVED true")), qPrintable(edited.right(600)));
+		const QString reopened = runChecked({QStringLiteral("--run"), dump, saved});
+		auto rowsOf = [](const QString &log) {
+			const int at = log.indexOf(QStringLiteral("ROWS "));
+			return at < 0 ? QString() : log.mid(at + 5, log.indexOf(QLatin1Char('\n'), at) - at - 5);
+		};
+		QVERIFY(!rowsOf(reopened).isEmpty());
+		QCOMPARE(rowsOf(edited), rowsOf(reopened));
+	}
+
+
 	// A title-block value that is a single space is kept through two saves
 	// (#973), and a value with accents comes back as it went in.
 	void singleSpaceValueKept()