Fix bugtracker #343: saving reorders texts and shapes after an edit

Diagram::toXml() writes texts, images, shapes and tables in items()
order. The diagram scene uses NoIndex, and Qt's linear index sorts its
item list by pointer address the first time any item is removed from
the scene, which the editor does constantly (selection handles, for
one). From then on the order in the saved file follows memory
addresses, so moving one element reshuffles unrelated blocks and a
version-control diff of the project becomes unreadable.

Write those blocks in stacking order instead, read from a rect query,
which Qt sorts by z and insertion order even with NoIndex. Reloading a
file rebuilds exactly that order, so a resave is stable and the drawing
does not change. Elements and conductors were already sorted.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01G2d2Zi8BfrYRPX88zhaoFG

sources/diagram.cpp

@@ -42,7 +42,9 @@
 #include "qetinformation.h"
 #include "qetproject.h"
 #include "diagramsortkeys.h"
+#include <QTextStream>
 #include <algorithm>
+#include <climits>
 #include <cassert>
 #include <math.h>
 
@@ -99,6 +101,43 @@ namespace {
 		QString b = terminalSortKey(cond->terminal2);
 		return (a <= b) ? (a + QLatin1Char('>') + b) : (b + QLatin1Char('>') + a);
 	}
+
+	/// Serialize @p items and append them to a new @p tag block of @p root,
+	/// in stacking order (@p stack_rank). items() cannot be trusted for
+	/// this: with NoIndex, the first removeItem() on the scene sorts Qt's
+	/// item list by pointer address, so from then on items() hands them over
+	/// in a per-run order (bugtracker #343). Stacking order is what reloading
+	/// the file rebuilds, so the drawing is unchanged and a resave is stable.
+	template <typename T>
+	void appendInStackingOrder(QDomDocument &document, QDomElement &root,
+							   const QString &tag, const QVector<T *> &items,
+							   const QHash<const QGraphicsItem *, int> &stack_rank)
+	{
+		if (items.isEmpty())
+			return;
+		struct Entry { int rank; QString xml_text; QDomElement xml; };
+		QVector<Entry> sorted;
+		for (T *item : items) {
+			Entry entry{stack_rank.value(item, INT_MAX), QString(),
+						item->toXml(document)};
+				// Only an item the stacking query missed needs a tiebreak.
+			if (entry.rank == INT_MAX) {
+				QTextStream stream(&entry.xml_text);
+				entry.xml.save(stream, 0);
+			}
+			sorted.append(entry);
+		}
+		std::stable_sort(sorted.begin(), sorted.end(),
+			[](const Entry &a, const Entry &b) {
+				return a.rank != b.rank ? a.rank < b.rank
+										: a.xml_text < b.xml_text;
+			});
+
+		auto block = document.createElement(tag);
+		for (const auto &entry : sorted)
+			block.appendChild(entry.xml);
+		root.appendChild(block);
+	}
 }
 
 int Diagram::xGrid  = 10;
@@ -1223,37 +1262,20 @@ QDomDocument Diagram::toXml(bool whole_content, bool is_copy_command) {
 		dom_root.appendChild(dom_conductors);
 	}
 
-	if (!list_texts.isEmpty()) {
-		auto dom_texts = document.createElement(QStringLiteral("inputs"));
-		for (auto dti : list_texts) {
-			dom_texts.appendChild(dti->toXml(document));
-		}
-		dom_root.appendChild(dom_texts);
-	}
-
-	if (!list_images.isEmpty()) {
-		auto dom_images = document.createElement(QStringLiteral("images"));
-		for (auto dii : list_images) {
-			dom_images.appendChild(dii->toXml(document));
-		}
-		dom_root.appendChild(dom_images);
-	}
-
-	if (!list_shapes.isEmpty()) {
-		auto dom_shapes = document.createElement(QStringLiteral("shapes"));
-		for (auto dii : list_shapes) {
-			dom_shapes.appendChild(dii -> toXml(document));
-		}
-		dom_root.appendChild(dom_shapes);
-	}
-
-	if (table_vector.size()) {
-		auto tables = document.createElement(QStringLiteral("tables"));
-		for (auto table : table_vector) {
-			tables.appendChild(table->toXml(document));
-		}
-		dom_root.appendChild(tables);
+		// A rect query, unlike items(), returns true stacking order (z, then
+		// insertion order) even with NoIndex.
+	QHash<const QGraphicsItem *, int> stack_rank;
+	{
+		const QList<QGraphicsItem *> stacked = items(
+					QRectF(-1e9, -1e9, 2e9, 2e9), Qt::IntersectsItemBoundingRect,
+					Qt::AscendingOrder);
+		for (int i = 0 ; i < stacked.size() ; ++i)
+			stack_rank.insert(stacked.at(i), i);
 	}
+	appendInStackingOrder(document, dom_root, QStringLiteral("inputs"), list_texts, stack_rank);
+	appendInStackingOrder(document, dom_root, QStringLiteral("images"), list_images, stack_rank);
+	appendInStackingOrder(document, dom_root, QStringLiteral("shapes"), list_shapes, stack_rank);
+	appendInStackingOrder(document, dom_root, QStringLiteral("tables"), table_vector, stack_rank);
 
 	if (!strip_vector.isEmpty()) {
 		dom_root.appendChild(TerminalStripItemXml::toXml(strip_vector, document));