fix placement of placeholder text in QLineEdits with action icons

After dc794f7622bc00f7ca50fab65d6965695d6d2972, side widgets only got
space if they were not fading out, but the logic was not correctly
accounting for side widgets that never fade, such as buttons added via
QLineEdit::addAction.

Fix this to give visible widgets space, unless they are fading out. That
was the intent of the original change. Rename the variable to make its
purpose clearer, and reset it at the end of the fade-out animation.

Add a much-needed test that relies on private APIs to verify that the
effective margins are calculated correctly.
Origin: upstream, https://code.qt.io/cgit/qt/qtbase.git/commit/?id=0e6b31019f01c72e
Last-Update: 2021-08-10

Gbp-Pq: Name fix-placement-of-placeholder-text-in-QLineEdits-with-action-icons.diff

src/widgets/widgets/qlineedit_p.cpp

@@ -407,8 +407,9 @@ void QLineEditIconButton::setHideWithText(bool hide)
 
 void QLineEditIconButton::onAnimationFinished()
 {
-    if (shouldHideWithText() && isVisible() && !m_wasHidden) {
+    if (shouldHideWithText() && isVisible() && m_fadingOut) {
         hide();
+        m_fadingOut = false;
 
         // Invalidate previous geometry to take into account new size of side widgets
         if (auto le = lineEditPrivate())
@@ -418,7 +419,7 @@ void QLineEditIconButton::onAnimationFinished()
 
 void QLineEditIconButton::animateShow(bool visible)
 {
-    m_wasHidden = visible;
+    m_fadingOut = !visible;
 
     if (shouldHideWithText() && !isVisible()) {
         show();

src/widgets/widgets/qlineedit_p.h

@@ -95,8 +95,11 @@ public:
 
     bool shouldHideWithText() const;
     void setHideWithText(bool hide);
-    // m_wasHidden is true unless the button is fading out
-    bool needsSpace() const { return m_wasHidden; }
+    bool needsSpace() const {
+        if (m_fadingOut)
+            return false;
+        return isVisibleTo(parentWidget());
+    }
 #endif
 
 protected:
@@ -120,7 +123,7 @@ private:
 
 #if QT_CONFIG(animation)
     bool m_hideWithText = false;
-    bool m_wasHidden = false;
+    bool m_fadingOut = false;
 #endif
 
 };

tests/auto/widgets/widgets/qlineedit/tst_qlineedit.cpp

@@ -292,6 +292,7 @@ private slots:
     void clearButtonVisibleAfterSettingText_QTBUG_45518();
     void sideWidgets();
     void sideWidgetsActionEvents();
+    void sideWidgetsEffectiveMargins();
 
     void shouldShowPlaceholderText_data();
     void shouldShowPlaceholderText();
@@ -4646,6 +4647,71 @@ void tst_QLineEdit::sideWidgetsActionEvents()
     QCOMPARE(toolButton2->x(), toolButton1X);
 }
 
+/*!
+    Verify that side widgets are positioned correctly and result in
+    correct effective text margins.
+*/
+void tst_QLineEdit::sideWidgetsEffectiveMargins()
+{
+#ifndef QT_BUILD_INTERNAL
+    QSKIP("This test requires a developer build.");
+#else
+    QLineEdit edit;
+    edit.setPlaceholderText("placeholder");
+    edit.setClearButtonEnabled(true);
+    edit.show();
+    QLineEditPrivate *priv = QLineEditPrivate::get(&edit);
+    const auto sideWidgetParameters = priv->sideWidgetParameters();
+    const int sideWidgetWidth = sideWidgetParameters.widgetWidth + sideWidgetParameters.margin;
+    QVERIFY(QTest::qWaitForWindowExposed(&edit));
+
+    QCOMPARE(priv->effectiveTextMargins().left(), 0);
+    QCOMPARE(priv->effectiveTextMargins().right(), 0);
+
+    edit.setText("Left to right"); // clear button fades in on the right
+    QCOMPARE(priv->effectiveTextMargins().left(), 0);
+    QCOMPARE(priv->effectiveTextMargins().right(), sideWidgetWidth);
+    edit.clear();
+    QCOMPARE(priv->effectiveTextMargins().left(), 0);
+    QCOMPARE(priv->effectiveTextMargins().right(), 0);
+
+    edit.setLayoutDirection(Qt::RightToLeft);
+    edit.setText("ئۇيغۇر تىلى"); // clear button fades in on the left
+    QCOMPARE(priv->effectiveTextMargins().left(), sideWidgetWidth);
+    QCOMPARE(priv->effectiveTextMargins().right(), 0);
+    edit.clear();
+    QCOMPARE(priv->effectiveTextMargins().left(), 0);
+    QCOMPARE(priv->effectiveTextMargins().right(), 0);
+
+    edit.setLayoutDirection(Qt::LeftToRight);
+
+    const QIcon leftIcon = edit.style()->standardIcon(QStyle::SP_FileIcon);
+    const QIcon rightIcon = edit.style()->standardIcon(QStyle::SP_DirIcon);
+    edit.addAction(leftIcon, QLineEdit::ActionPosition::LeadingPosition);
+    QCOMPARE(priv->effectiveTextMargins().left(), sideWidgetWidth);
+    QCOMPARE(priv->effectiveTextMargins().right(), 0);
+
+    edit.addAction(rightIcon, QLineEdit::ActionPosition::TrailingPosition);
+    QCOMPARE(priv->effectiveTextMargins().left(), sideWidgetWidth);
+    QCOMPARE(priv->effectiveTextMargins().right(), sideWidgetWidth);
+
+    edit.setText("Left to right"); // clear button on the right
+    QCOMPARE(priv->effectiveTextMargins().left(), sideWidgetWidth);
+    QCOMPARE(priv->effectiveTextMargins().right(), 2 * sideWidgetWidth);
+    edit.clear();
+    QCOMPARE(priv->effectiveTextMargins().left(), sideWidgetWidth);
+    QCOMPARE(priv->effectiveTextMargins().right(), sideWidgetWidth);
+
+    edit.setLayoutDirection(Qt::RightToLeft);
+    edit.setText("ئۇيغۇر تىلى"); // clear button fades in on the left
+    QCOMPARE(priv->effectiveTextMargins().left(), 2 * sideWidgetWidth);
+    QCOMPARE(priv->effectiveTextMargins().right(), sideWidgetWidth);
+    edit.clear();
+    QCOMPARE(priv->effectiveTextMargins().left(), sideWidgetWidth);
+    QCOMPARE(priv->effectiveTextMargins().right(), sideWidgetWidth);
+#endif
+}
+
 Q_DECLARE_METATYPE(Qt::AlignmentFlag)
 void tst_QLineEdit::shouldShowPlaceholderText_data()
 {