Fix Project properties > OK marking the project modified with no edit

Pressing OK in Projet > Propriétés du projet without changing anything
marked the project modified and rewrote its defaults for new folios.
Besides the Page Num placeholder (fixed separately), four causes:

- Title block custom fields: since #271 the dialog offers the
  template's variables for filling in; those left empty came back as
  part of the context. Drop the ones not in the stored context.
- DiagramContext::remove() left the key's show flag behind, so a
  context with a key removed never equalled one without it.
- Guides: applyConf() marked the project modified whether or not the
  guides changed. Compare them like every other setting.
- Wire dash size and cross-reference offsets: the spin boxes cannot
  show the stored default (dash size 1 under a minimum of 2; offset 0
  under a minimum of 40 shown as "Default"), so the clamped value came
  back. Keep the stored value unless the box shows something else, as
  #1204 did for the wire panel.

Checked in the GUI (with the Page Num fix as well) on grafcet,
schema_indus and Projet_vierge: OK with no edit then Ctrl+S saves the
same file as Ctrl+S alone; master writes dash-size 1 -> 2, a
cross-reference offset 0 -> 40, and on Projet_vierge 22 empty custom
fields. New test for DiagramContext::remove() fails without the fix.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

sources/diagramcontext.cpp

@@ -42,6 +42,7 @@ void DiagramContext::add(DiagramContext other)
 */
 void DiagramContext::remove(const QString &key) {
 	m_content.remove(key);
+	m_content_show.remove(key);
 }
 
 /**

sources/ui/conductorpropertieswidget.cpp

@@ -126,6 +126,12 @@ ConductorProperties ConductorPropertiesWidget::properties() const
 	properties_.m_bicolor               = ui->m_color_2_gb->isChecked();
 	properties_.m_color_2               = ui->m_color_2_kpb->color();
 	properties_.m_dash_size             = ui->m_dash_size_sb->value();
+		//The box starts at 2, so the default size 1 shows as 2: keep the
+		//stored size unless the box shows something else.
+	if (properties_.m_dash_size == qBound(ui->m_dash_size_sb->minimum(),
+										  m_properties.m_dash_size,
+										  ui->m_dash_size_sb->maximum()))
+		properties_.m_dash_size = m_properties.m_dash_size;
 	properties_.style                   = ui -> m_line_style_cb->itemData(ui->m_line_style_cb->currentIndex()).value<QPen>().style();
 	properties_.m_formula               = ui->m_formula_le->text();
 	properties_.text                    = ui -> m_text_le -> text();

sources/ui/configpage/configpages.cpp

@@ -233,8 +233,10 @@ void NewDiagramPage::applyConf()
 			pg.color = g.color;
 			proj_guides.append(pg);
 		}
-		m_project->setDefaultGuides(proj_guides);
-		modified_project = true;
+		if (m_project->defaultGuides() != proj_guides) {
+			m_project->setDefaultGuides(proj_guides);
+			modified_project = true;
+		}
 
 		if (modified_project) {
 			m_project -> setModified(modified_project);

sources/ui/titleblockpropertieswidget.cpp

@@ -166,6 +166,7 @@ void TitleBlockPropertiesWidget::setProperties(
 	// Show the saved custom values, plus any of the template's custom variables
 	// that aren't defined yet, so the user only fills in the missing ones (#271).
 	DiagramContext context = properties.context;
+	m_context_keys = context.keys();
 	addTemplateVariables(context, index);
 	m_dcw -> setContext(context);
 }
@@ -215,6 +216,14 @@ TitleBlockProperties TitleBlockPropertiesWidget::properties() const
 	}
 
 	prop.context = m_dcw -> context();
+		//The template's custom variables are only offered for filling in
+		//(#271): one left empty is not part of the properties.
+	const QList<QString> keys = prop.context.keys();
+	for (const QString &key : keys) {
+		if (!m_context_keys.contains(key)
+				&& prop.context.value(key).toString().isEmpty())
+			prop.context.remove(key);
+	}
 
 	prop.auto_page_num = ui->auto_page_cb->currentText();
 

sources/ui/titleblockpropertieswidget.h

@@ -100,6 +100,8 @@ class TitleBlockPropertiesWidget : public QWidget
 	private:
 		Ui::TitleBlockPropertiesWidget *ui;
 		DiagramContextWidget *m_dcw;
+			/// keys of the context given to setProperties()
+		QStringList m_context_keys;
 		QAction *m_tbt_edit, *m_tbt_duplicate;
 		QMenu *m_tbt_menu;
 		QList <TitleBlockTemplatesCollection *> m_tbt_collection_list;

sources/ui/xrefpropertieswidget.cpp

@@ -151,8 +151,15 @@ void XRefPropertiesWidget::saveProperties(int index) {
 	xrp.setPrefix("switch", ui->m_switch_prefix_le->text());
 	xrp.setMasterLabel(ui->m_master_le->text());
 	xrp.setSlaveLabel(ui->m_slave_le->text());
-	xrp.setOffset(ui->m_offset_sb->value());
-	xrp.setSlaveOffset(ui->m_slave_offset_sb->value());
+		//The boxes cannot show a value below their minimum (the offset's
+		//minimum is its "Default" entry, standing for the stored 0): keep
+		//the stored value unless the box shows something else.
+	if (ui->m_offset_sb->value() != qBound(ui->m_offset_sb->minimum(), xrp.offset(),
+										   ui->m_offset_sb->maximum()))
+		xrp.setOffset(ui->m_offset_sb->value());
+	if (ui->m_slave_offset_sb->value() != qBound(ui->m_slave_offset_sb->minimum(), xrp.slaveOffset(),
+												 ui->m_slave_offset_sb->maximum()))
+		xrp.setSlaveOffset(ui->m_slave_offset_sb->value());
 
 	m_properties.insert(type, xrp);
 }

tests/qttest/tst_diagramcontext.cpp

@@ -65,6 +65,24 @@ private slots:
 		QCOMPARE(fromDom(xml(value)), expected);
 		QCOMPARE(fromPugi(xml(value)), expected);
 	}
+
+		// remove() forgets the key entirely: a context with a key added
+		// then removed equals one that never had it. remove() used to keep
+		// the key's show flag, so the two never compared equal, and
+		// Project properties > OK saw a change where there was none.
+	void removeForgetsTheKey()
+	{
+		DiagramContext edited;
+		edited.addValue(QStringLiteral("author"), QStringLiteral("N.V."));
+		edited.addValue(QStringLiteral("01-numprojet"), QString());
+		edited.remove(QStringLiteral("01-numprojet"));
+
+		DiagramContext stored;
+		stored.addValue(QStringLiteral("author"), QStringLiteral("N.V."));
+
+		QCOMPARE(edited.keys(), stored.keys());
+		QVERIFY(edited == stored);
+	}
 };
 
 QTEST_APPLESS_MAIN(tst_diagramcontext)