Positioner: Conditionally skip saving positions after listing completes

Prevent saving incorrect icon positions while the desktop is still
setting up its screen geometry.

This fixes the following scenario:
- 'setPerStripe()' is called from QtQuick with a lower 'perStripe'
  value (because the desktop geometry is not yet correct) while the
  directory is being listed
- directory listing finishes (we skip saving the icon positions)
- 'setPerStripe()' is called again (from QtQuick) with the correct value

This can occasionally happen when turning off one monitor and turning on
another, depending on the hardware.

Behavior change: Saving is skipped when Plasma loads or the desktop
reappears on the screen. There is no need to save when the desktop
loads or reappears.

containments/desktop/plugins/folder/autotests/positionertest.cpp

@@ -418,6 +418,44 @@ void PositionerTest::tst_dontSaveWithoutScreen()
     QCOMPARE(baselineConfig, getCurrentConfig());
 }
 
+void PositionerTest::tst_mixedSetPerStripeListingAndReady()
+{
+    QString firstUrl;
+    for (auto [url, gridPos] : std::as_const(m_positioner->m_positions).asKeyValueRange()) {
+        if (gridPos.pos == 0 && gridPos.stripe == 0) {
+            firstUrl = url;
+            break;
+        }
+    }
+    QVERIFY(!firstUrl.isEmpty());
+
+    auto getFirstGridPos = [firstUrl, this] {
+        return m_positioner->m_positions.value(firstUrl, {-1, -1});
+    };
+
+    const auto perStripe = m_positioner->perStripe();
+    QCOMPARE_GT(perStripe, 1);
+
+    const int newPos = m_positioner->m_positions.size() + perStripe + 1;
+    m_positioner->move({0, newPos});
+
+    auto newGridPos = getFirstGridPos();
+    QCOMPARE(newGridPos.stripe, newPos / perStripe);
+    QCOMPARE(newGridPos.pos, newPos % perStripe);
+
+    m_folderModel->refresh();
+    QTRY_COMPARE(m_folderModel->status(), FolderModel::Listing);
+
+    m_positioner->setPerStripe(1);
+    QVERIFY(m_positioner->m_deferApplyPositions);
+    ensureFolderModelReady();
+    m_positioner->setPerStripe(perStripe);
+
+    auto gridPos = getFirstGridPos();
+    QCOMPARE(gridPos.stripe, newGridPos.stripe);
+    QCOMPARE(gridPos.pos, newGridPos.pos);
+}
+
 // Test utilities
 
 QJsonDocument PositionerTest::getCurrentConfig()

containments/desktop/plugins/folder/autotests/positionertest.h

@@ -48,6 +48,7 @@ private Q_SLOTS:
     void tst_renameFile();
     void tst_insertFile();
     void tst_dontSaveWithoutScreen();
+    void tst_mixedSetPerStripeListingAndReady();
 
 private:
     void checkDefaultPositions(int perStripe);

containments/desktop/plugins/folder/positioner.cpp

@@ -570,6 +570,7 @@ void Positioner::sourceStatusChanged()
             updatePositionsList();
             if (m_deferRestoreChangedPositions) {
                 maybeRestoreAndApplyChangedPositions(false);
+                m_skipSaveOnListingCompleted = (m_folderModel->status() == FolderModel::Ready);
             }
         }
     }
@@ -1328,7 +1329,11 @@ void Positioner::onListingCompleted(const QList<QUrl> &urls)
 
     m_positions = newPositions;
 
-    savePositionsConfig();
+    if (m_skipSaveOnListingCompleted) {
+        m_skipSaveOnListingCompleted = false;
+    } else {
+        savePositionsConfig();
+    }
 }
 
 void Positioner::connectSignals(FolderModel *model)

containments/desktop/plugins/folder/positioner.h

@@ -178,6 +178,7 @@ private:
     QHash<QString, GridPosition> m_positions;
     bool m_deferApplyPositions;
     bool m_deferRestoreChangedPositions = false;
+    bool m_skipSaveOnListingCompleted = false;
     QVariantList m_deferMovePositions;
 
     QHash<QString, std::optional<ChangedPosition>> m_changedPositions;