Never use a folio grid step below 1 from the settings

The folio grid steps, diagrameditor/Xgrid and Ygrid, are read from the
settings in six places with a plain toInt() and used as they come. The
preferences page cannot store anything below 1, but a hand-edited or
damaged settings file can hold 0, a negative number or text:

- Diagram::snapToGrid() divides by the step, so 0 is a SIGFPE on the
  first click that places a symbol;
- Diagram::drawBackground() runs "while (g_x % xGrid)" and then loops
  "gx += xGrid", so 0 crashes every repaint and a negative step never
  ends;
- the paste, duplicate and align paths divide by it or multiply with it.

Add foliogrid.h, a header-only helper: FolioGrid::step() reads a
settings entry and returns the built-in step (Diagram::xGrid, 10) when
the entry is missing, not a number, below 1 or above what an int
holds (QVariant::toInt() wraps such a value around). Every reader of
the two keys goes through it; the settings page, which only writes the
spin box values, is unchanged.

No file-format change, and no change for any step the preferences page
can produce.

Tests: tst_foliogrid covers the helper: 1, 10, "7", int max are kept;
missing, 0, -5, "ten", "", "nan", 99999999999 (as text and as a
number) and int max + 1 fall back; 7.9 rounds to 8 as before; and the
two settings keys through a QSettings scope of the test's own. The
helper is new, so the test cannot fail on master; the six readers are
the replacements in the diff.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Signed-off-by: Beat Hangartner <beat@hangartners.ch>

sources/diagram.cpp

@@ -45,6 +45,7 @@
 #include "diagramsortkeys.h"
 #include "itemgroups.h"
 #include "textgrid.h"
+#include "foliogrid.h"
 #include <QGraphicsView>
 #include <QTextStream>
 #include <algorithm>
@@ -339,10 +340,8 @@ void Diagram::drawBackground(QPainter *p, const QRectF &r) {
 
 		p -> setBrush(Qt::NoBrush);
 
-		int xGrid = settings.value(QStringLiteral("diagrameditor/Xgrid"),
-								   Diagram::xGrid).toInt();
-		int yGrid = settings.value(QStringLiteral("diagrameditor/Ygrid"),
-								   Diagram::yGrid).toInt();
+		const int xGrid = FolioGrid::step(settings.value(FolioGrid::x_key), Diagram::xGrid);
+		const int yGrid = FolioGrid::step(settings.value(FolioGrid::y_key), Diagram::yGrid);
 
 		qreal limit_x = rect.x() + rect.width();
 		qreal limit_y = rect.y() + rect.height();
@@ -2946,10 +2945,8 @@ DiagramPosition Diagram::convertPosition(const QPointF &pos) {
 QPointF Diagram::snapToGrid(const QPointF &p)
 {
 	QSettings settings;
-	int xGrid = settings.value(QStringLiteral("diagrameditor/Xgrid"),
-							   Diagram::xGrid).toInt();
-	int yGrid = settings.value(QStringLiteral("diagrameditor/Ygrid"),
-							   Diagram::yGrid).toInt();
+	const int xGrid = FolioGrid::step(settings.value(FolioGrid::x_key), Diagram::xGrid);
+	const int yGrid = FolioGrid::step(settings.value(FolioGrid::y_key), Diagram::yGrid);
 
 	//Return a point rounded to the nearest pixel
 	if (QApplication::keyboardModifiers().testFlag(Qt::ControlModifier))
@@ -2981,10 +2978,8 @@ QPointF Diagram::snapToTextGrid(const QPointF &p)
 			: settings.value(TextGrid::settings_key, 1).toReal();
 
 	return TextGrid::snap(p,
-						  settings.value(QStringLiteral("diagrameditor/Xgrid"),
-										 Diagram::xGrid).toInt(),
-						  settings.value(QStringLiteral("diagrameditor/Ygrid"),
-										 Diagram::yGrid).toInt(),
+						  FolioGrid::step(settings.value(FolioGrid::x_key), Diagram::xGrid),
+						  FolioGrid::step(settings.value(FolioGrid::y_key), Diagram::yGrid),
 						  divisor);
 }
 

sources/diagramevent/diagrameventaddpaste.cpp

@@ -19,6 +19,7 @@
 #include "../autoNum/ui/pastenumberingimport.h"
 
 #include "../diagram.h"
+#include "../foliogrid.h"
 #include "../diagramcommands.h"
 #include "../qetapp.h"
 #include "../qetdiagrameditor.h"
@@ -108,10 +109,8 @@
 	}
 	const QPointF top_left = items_rect.topLeft();
 	QSettings settings;
-	const int xGrid = settings.value(QStringLiteral("diagrameditor/Xgrid"),
-					  Diagram::xGrid).toInt();
-	const int yGrid = settings.value(QStringLiteral("diagrameditor/Ygrid"),
-					  Diagram::yGrid).toInt();
+	const int xGrid = FolioGrid::step(settings.value(FolioGrid::x_key), Diagram::xGrid);
+	const int yGrid = FolioGrid::step(settings.value(FolioGrid::y_key), Diagram::yGrid);
 	const auto snapGrid = [xGrid, yGrid](const QPointF &p) -> QPointF {
 		return QPointF(
 			qRound(p.x() / xGrid) * xGrid,
@@ -287,10 +286,8 @@ void DiagramEventAddPaste::showHint()
 void DiagramEventAddPaste::moveTo(const QPointF &scene_pos)
 {
 	QSettings settings;
-	const int xGrid = settings.value(QStringLiteral("diagrameditor/Xgrid"),
-					  Diagram::xGrid).toInt();
-	const int yGrid = settings.value(QStringLiteral("diagrameditor/Ygrid"),
-					  Diagram::yGrid).toInt();
+	const int xGrid = FolioGrid::step(settings.value(FolioGrid::x_key), Diagram::xGrid);
+	const int yGrid = FolioGrid::step(settings.value(FolioGrid::y_key), Diagram::yGrid);
 
 	const auto snapGrid = [xGrid, yGrid](const QPointF &p) -> QPointF {
 		return QPointF(

sources/diagramview.cpp

@@ -40,6 +40,7 @@
 #include "utils/conductorcreator.h"
 #include "undocommand/addgraphicsobjectcommand.h"
 #include "diagram.h"
+#include "foliogrid.h"
 #include "diagramcontexttoolbar.h"
 #include "diagramgestureoverlay.h"
 #include "gesturesettings.h"
@@ -643,10 +644,8 @@ void DiagramView::duplicate(const QPoint &stepOffset)
 	if (selection.isEmpty()) return;
 
 	QSettings settings;
-	const int x_grid = settings.value(QStringLiteral("diagrameditor/Xgrid"),
-									  Diagram::xGrid).toInt();
-	const int y_grid = settings.value(QStringLiteral("diagrameditor/Ygrid"),
-									  Diagram::yGrid).toInt();
+	const int x_grid = FolioGrid::step(settings.value(FolioGrid::x_key), Diagram::xGrid);
+	const int y_grid = FolioGrid::step(settings.value(FolioGrid::y_key), Diagram::yGrid);
 	const QPointF offset(stepOffset.x() * x_grid, stepOffset.y() * y_grid);
 
 	// Mirrors copy(), but does not touch the system clipboard: Ctrl+D

sources/foliogrid.h

@@ -0,0 +1,54 @@
+/*
+	Copyright 2006-2026 The QElectroTech Team
+	This file is part of QElectroTech.
+
+	QElectroTech is free software: you can redistribute it and/or modify
+	it under the terms of the GNU General Public License as published by
+	the Free Software Foundation, either version 2 of the License, or
+	(at your option) any later version.
+
+	QElectroTech is distributed in the hope that it will be useful,
+	but WITHOUT ANY WARRANTY; without even the implied warranty of
+	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+	GNU General Public License for more details.
+
+	You should have received a copy of the GNU General Public License
+	along with QElectroTech.  If not, see <http://www.gnu.org/licenses/>.
+*/
+#ifndef FOLIOGRID_H
+#define FOLIOGRID_H
+
+#include <QString>
+#include <QVariant>
+#include <limits>
+
+/**
+	The folio grid: the step, in pixels, that symbols snap to. Both steps
+	are kept in the settings; the preferences page only offers 1 and up,
+	but a hand-edited or damaged settings file can hold 0, a negative
+	number or text, and the code that divides by the step or loops over it
+	must never see such a value.
+*/
+namespace FolioGrid
+{
+		/// QSettings keys holding the two steps.
+	inline const QString x_key{QStringLiteral("diagrameditor/Xgrid")};
+	inline const QString y_key{QStringLiteral("diagrameditor/Ygrid")};
+
+	/**
+		@return the step held in @p value, a settings entry; or @p fallback,
+		the built-in step, when the entry is missing, not a number, less
+		than 1, or more than an int holds (QVariant::toInt() wraps such a
+		number around instead of failing).
+	*/
+	inline int step(const QVariant &value, int fallback)
+	{
+		bool ok = false;
+		const qlonglong s = value.toLongLong(&ok);
+		if (!ok || s < 1 || s > std::numeric_limits<int>::max())
+			return fallback;
+		return int(s);
+	}
+}
+
+#endif // FOLIOGRID_H

sources/undocommand/alignselectioncommand.cpp

@@ -20,6 +20,7 @@
 #include "../QPropertyUndoCommand/qpropertyundocommand.h"
 #include "../alignment.h"
 #include "../diagram.h"
+#include "../foliogrid.h"
 #include "../diagramcontent.h"
 #include "../itemgroups.h"
 #include "../qetgraphicsitem/diagramimageitem.h"
@@ -121,8 +122,8 @@ AlignSelectionCommand::AlignSelectionCommand(Diagram *diagram, Mode mode, QUndoC
 	m_locked_count = dc.removeNonMovableItems();
 
 	QSettings settings;
-	const int x_grid = settings.value(QStringLiteral("diagrameditor/Xgrid"), Diagram::xGrid).toInt();
-	const int y_grid = settings.value(QStringLiteral("diagrameditor/Ygrid"), Diagram::yGrid).toInt();
+	const int x_grid = FolioGrid::step(settings.value(FolioGrid::x_key), Diagram::xGrid);
+	const int y_grid = FolioGrid::step(settings.value(FolioGrid::y_key), Diagram::yGrid);
 	const qreal text_divisor = settings.value(TextGrid::settings_key, 1).toReal();
 
 		//Each kind goes where dragging it would have left it: symbols,

tests/qttest/CMakeLists.txt

@@ -128,6 +128,13 @@ add_test(NAME tst_textgrid COMMAND tst_textgrid)
 target_include_directories(tst_textgrid PRIVATE ${QET_DIR}/sources)
 target_link_libraries(tst_textgrid PRIVATE Qt::Test)
 
+# foliogrid.h is header-only: the folio grid step as read from the
+# settings, never 0 or negative, so no reader can divide by it or loop on it.
+add_executable(tst_foliogrid tst_foliogrid.cpp)
+target_include_directories(tst_foliogrid PRIVATE ${QET_DIR}/sources)
+target_link_libraries(tst_foliogrid PRIVATE Qt::Test Qt::Core)
+add_test(NAME tst_foliogrid COMMAND tst_foliogrid)
+
 # textlines.h is header-only: the lines of a text as they are laid out,
 # for the exports that write a text line by line.
 add_executable(tst_textlines tst_textlines.cpp)

tests/qttest/tst_foliogrid.cpp

@@ -0,0 +1,99 @@
+/*
+	Copyright 2006-2026 The QElectroTech Team
+	This file is part of QElectroTech.
+
+	QElectroTech is free software: you can redistribute it and/or modify
+	it under the terms of the GNU General Public License as published by
+	the Free Software Foundation, either version 2 of the License, or
+	(at your option) any later version.
+
+	QElectroTech is distributed in the hope that it will be useful,
+	but WITHOUT ANY WARRANTY; without even the implied warranty of
+	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+	GNU General Public License for more details.
+
+	You should have received a copy of the GNU General Public License
+	along with QElectroTech.  If not, see <http://www.gnu.org/licenses/>.
+*/
+#include "foliogrid.h"
+
+#include <QtTest>
+#include <QSettings>
+
+/**
+	FolioGrid::step() -- the folio grid step as read from the settings.
+	Every reader of diagrameditor/Xgrid and Ygrid goes through it, so a
+	settings file holding 0 (a division by zero in Diagram::snapToGrid()
+	and an endless "% 0" in drawBackground()), a negative number (an
+	endless loop) or text can no longer reach the code that uses the step.
+*/
+class tst_foliogrid : public QObject
+{
+	Q_OBJECT
+
+private slots:
+	void usableValuesAreKept_data()
+	{
+		QTest::addColumn<QVariant>("value");
+		QTest::addColumn<int>("expected");
+		QTest::newRow("one")          << QVariant(1) << 1;
+		QTest::newRow("default")      << QVariant(10) << 10;
+		QTest::newRow("text number")  << QVariant(QStringLiteral("7")) << 7;
+		QTest::newRow("large")        << QVariant(100000) << 100000;
+		QTest::newRow("int max")      << QVariant(2147483647) << 2147483647;
+	}
+
+	void usableValuesAreKept()
+	{
+		QFETCH(QVariant, value);
+		QFETCH(int, expected);
+		QCOMPARE(FolioGrid::step(value, 10), expected);
+	}
+
+	void unusableValuesFallBack_data()
+	{
+		QTest::addColumn<QVariant>("value");
+		QTest::newRow("missing")   << QVariant();
+		QTest::newRow("zero")      << QVariant(0);
+		QTest::newRow("negative")  << QVariant(-5);
+		QTest::newRow("text")      << QVariant(QStringLiteral("ten"));
+		QTest::newRow("empty")     << QVariant(QString());
+		QTest::newRow("nan")       << QVariant(QStringLiteral("nan"));
+		QTest::newRow("too large") << QVariant(QStringLiteral("99999999999"));
+		QTest::newRow("too large number") << QVariant(qlonglong(99999999999));
+		QTest::newRow("int max + 1") << QVariant(qlonglong(2147483648));
+	}
+
+	void unusableValuesFallBack()
+	{
+		QFETCH(QVariant, value);
+		QCOMPARE(FolioGrid::step(value, 10), 10);
+		QCOMPARE(FolioGrid::step(value, 20), 20);
+	}
+
+	// A decimal in the file is rounded to a whole number, as the plain
+	// QVariant::toInt() read did before.
+	void decimalIsRoundedLikeBefore()
+	{
+		QCOMPARE(FolioGrid::step(QVariant(7.9), 10), 8);
+		QCOMPARE(FolioGrid::step(QVariant(0.4), 10), 10);
+	}
+
+	// Through a real settings file, in a scope of this test's own.
+	void readsTheSettingsKeys()
+	{
+		QCoreApplication::setOrganizationName(QStringLiteral("QElectroTech-tst_foliogrid"));
+		QCoreApplication::setApplicationName(QStringLiteral("tst_foliogrid"));
+		QSettings settings;
+		settings.clear();
+		QCOMPARE(FolioGrid::step(settings.value(FolioGrid::x_key), 10), 10);
+		settings.setValue(FolioGrid::x_key, 0);
+		settings.setValue(FolioGrid::y_key, 15);
+		QCOMPARE(FolioGrid::step(settings.value(FolioGrid::x_key), 10), 10);
+		QCOMPARE(FolioGrid::step(settings.value(FolioGrid::y_key), 10), 15);
+		settings.clear();
+	}
+};
+
+QTEST_GUILESS_MAIN(tst_foliogrid)
+#include "tst_foliogrid.moc"