Prevent editor clipping in narrow windows

src/Main.qml

@@ -26,9 +26,12 @@ ApplicationWindow {
     // the app at the sizes it was designed around.
     readonly property real textScale: backend.textScale
     readonly property int editorFontPixelSize: scaledSize(20)
+    // Never wider than the Flickable's viewport, whatever the floor asks for:
+    // a tiling compositor can resize the window below its minimum width.
     readonly property int editorWidth: Math.min(
         Math.round(writerFontMetrics.averageCharacterWidth * 65),
-        Math.max(360, width - Math.round(writerFontMetrics.averageCharacterWidth * 20)))
+        Math.max(360, width - Math.round(writerFontMetrics.averageCharacterWidth * 20)),
+        Math.max(0, width - 48))
     property bool closeConfirmed: false
     property bool searchOpen: false
     property bool searchUpdating: false

tests/tst_omawrite.cpp

@@ -218,6 +218,40 @@ private slots:
         QCOMPARE(editor->property("font").value<QFont>().pixelSize(), 15);
     }
 
+    void keepsTextColumnInsideNarrowWindows() {
+        const QString mainQmlPath = QFINDTESTDATA("../src/Main.qml");
+        QVERIFY(!mainQmlPath.isEmpty());
+
+        Backend backend;
+        QQmlEngine engine;
+        engine.rootContext()->setContextProperty(QStringLiteral("backend"), &backend);
+        QQmlComponent component(&engine, QUrl::fromLocalFile(mainQmlPath));
+        QVERIFY2(component.isReady(), qPrintable(component.errorString()));
+        QScopedPointer<QObject> window(component.create());
+        QVERIFY2(window, qPrintable(component.errorString()));
+
+        QObject *editor = window->findChild<QObject *>(QStringLiteral("sourceEditor"));
+        QVERIFY(editor);
+        QObject *viewport = editor->parent();
+        QVERIFY(viewport);
+
+        // A resize reaches the window through its platform window, so the
+        // bindings only see the new width once the events are delivered.
+        const int minimumWidth = window->property("minimumWidth").toInt();
+        window->setProperty("width", minimumWidth);
+        QCoreApplication::processEvents();
+        QCOMPARE(window->property("width").toInt(), minimumWidth);
+        QVERIFY(editor->property("x").toInt() > 0);
+
+        // A tiling compositor resizes below the minimum the window asks for.
+        window->setProperty("width", 394);
+        QCoreApplication::processEvents();
+        QCOMPARE(window->property("width").toInt(), 394);
+        QVERIFY(editor->property("width").toInt()
+                <= viewport->property("width").toInt());
+        QVERIFY(editor->property("x").toInt() >= 0);
+    }
+
     void remembersLastSaveDirectory() {
         QTemporaryDir saveDirectory;
         QVERIFY(saveDirectory.isValid());