QPlainTextEdit: fix the visibility of placeholderText

If one calls setPlainText("") before setting a placeholder text,
the placeholder visibility is not updated, and the placeholder is not
visible. Fix it by updating placeholderVisible properly.

Fixes: QTBUG-96212
Pick-to: 5.15 6.2 6.3
Change-Id: I1bd3f0cb4c59973a847bcf3787e35d7c17b6d673
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>

src/widgets/widgets/qplaintextedit.cpp

@@ -793,7 +793,7 @@ void QPlainTextEditPrivate::init(const QString &txt)
     QObject::connect(control, SIGNAL(selectionChanged()), q, SIGNAL(selectionChanged()));
     QObject::connect(control, SIGNAL(cursorPositionChanged()), q, SLOT(_q_cursorPositionChanged()));
 
-    QObject::connect(control, SIGNAL(textChanged()), q, SLOT(_q_textChanged()));
+    QObject::connect(control, SIGNAL(textChanged()), q, SLOT(_q_updatePlaceholderVisibility()));
     QObject::connect(control, SIGNAL(textChanged()), q, SLOT(updateMicroFocus()));
 
     // set a null page size initially to avoid any relayouting until the textedit
@@ -822,7 +822,7 @@ void QPlainTextEditPrivate::init(const QString &txt)
 #endif
 }
 
-void QPlainTextEditPrivate::_q_textChanged()
+void QPlainTextEditPrivate::_q_updatePlaceholderVisibility()
 {
     Q_Q(QPlainTextEdit);
 
@@ -1368,8 +1368,7 @@ void QPlainTextEdit::setPlaceholderText(const QString &placeholderText)
     Q_D(QPlainTextEdit);
     if (d->placeholderText != placeholderText) {
         d->placeholderText = placeholderText;
-        if (d->control->document()->isEmpty())
+        d->_q_updatePlaceholderVisibility();
-            d->viewport->update();
     }
 }
 

src/widgets/widgets/qplaintextedit.h

@@ -277,7 +277,7 @@ protected:
 private:
     Q_DISABLE_COPY(QPlainTextEdit)
     Q_PRIVATE_SLOT(d_func(), void _q_repaintContents(const QRectF &r))
-    Q_PRIVATE_SLOT(d_func(), void _q_textChanged())
+    Q_PRIVATE_SLOT(d_func(), void _q_updatePlaceholderVisibility())
     Q_PRIVATE_SLOT(d_func(), void _q_adjustScrollbars())
     Q_PRIVATE_SLOT(d_func(), void _q_verticalScrollbarActionTriggered(int))
     Q_PRIVATE_SLOT(d_func(), void _q_cursorPositionChanged())

src/widgets/widgets/qplaintextedit_p.h

@@ -121,7 +121,7 @@ public:
 
     void init(const QString &txt = QString());
     void _q_repaintContents(const QRectF &contentsRect);
-    void _q_textChanged();
+    void _q_updatePlaceholderVisibility();
 
     inline QPoint mapToContents(const QPoint &point) const
         { return QPoint(point.x() + horizontalOffset(), point.y() + verticalOffset()); }

tests/auto/widgets/widgets/qplaintextedit/tst_qplaintextedit.cpp

@@ -38,6 +38,7 @@
 #include <qclipboard.h>
 #include <qtextbrowser.h>
 #include <private/qwidgettextcontrol_p.h>
+#include <private/qplaintextedit_p.h>
 #include <qscrollbar.h>
 #include <qtextobject.h>
 #include <qmenu.h>
@@ -154,6 +155,8 @@ private slots:
     void updateCursorPositionAfterEdit();
 #endif
     void appendTextWhenInvisible();
+    void placeholderVisibility_data();
+    void placeholderVisibility();
 
 private:
     void createSelection();
@@ -1837,5 +1840,107 @@ void tst_QPlainTextEdit::appendTextWhenInvisible()
     QCOMPARE(maxAfterAppend, maxAfterSet);
 }
 
+enum SetupCommand {
+    ClearPlaceHolder, // set empty placeholder text
+    SetPlaceHolder, // set a non-empty placeholder text
+    ClearContent, // set empty text as content
+    SetContent // set non-empty text as content
+};
+
+void tst_QPlainTextEdit::placeholderVisibility_data()
+{
+    QTest::addColumn<QList<SetupCommand>>("setupCommands");
+    QTest::addColumn<bool>("placeholderVisible");
+    QTest::addRow("no placeholder set + no text set")
+            << QList<SetupCommand>{} << true;
+    QTest::addRow("no placeholder set + text set or text set + no placeholder set")
+            << QList<SetupCommand>{ SetContent } << false;
+    QTest::addRow("no placeholder set + text set + empty text set")
+            << QList<SetupCommand>{ SetContent , ClearContent }
+            << false;
+    QTest::addRow("no placeholder set + empty text set + text set")
+            << QList<SetupCommand>{ ClearContent, SetContent }
+            << false;
+    QTest::addRow("empty placeholder set + no text set")
+            << QList<SetupCommand>{ ClearPlaceHolder } << true;
+    QTest::addRow("empty placeholder set + text set")
+            << QList<SetupCommand>{ ClearPlaceHolder, SetContent }
+            << false;
+    QTest::addRow("empty placeholder set + text set + empty text set")
+            << QList<SetupCommand>{ ClearPlaceHolder, SetContent, ClearContent }
+            << false;
+    QTest::addRow("empty placeholder set + empty text set + text set")
+            << QList<SetupCommand>{ ClearPlaceHolder, ClearContent, SetContent }
+            << false;
+    QTest::addRow("placeholder set + no text set")
+            << QList<SetupCommand>{ SetPlaceHolder, ClearContent }
+            << true;
+    QTest::addRow("placeholder set + text set")
+            << QList<SetupCommand>{ SetPlaceHolder, SetContent }
+            << false;
+    QTest::addRow("placeholder set + text set + empty text set")
+            << QList<SetupCommand>{ SetPlaceHolder, SetContent, ClearContent }
+            << true;
+    QTest::addRow("placeholder set + empty text set + text set")
+            << QList<SetupCommand>{ SetPlaceHolder, ClearContent, SetContent }
+            << false;
+    QTest::addRow("placeholder set + text set + empty placeholder set")
+            << QList<SetupCommand>{ SetPlaceHolder, SetContent, ClearPlaceHolder}
+            << false;
+    QTest::addRow("placeholder set + empty placeholder set + text set")
+            << QList<SetupCommand>{ SetPlaceHolder, ClearPlaceHolder, SetContent }
+            << false;
+    QTest::addRow("placeholder set + empty placeholder set + empty text set")
+            << QList<SetupCommand>{ SetPlaceHolder, ClearPlaceHolder, ClearContent }
+            << false;
+    QTest::addRow("placeholder set + empty text set + empty placeholder set")
+            << QList<SetupCommand>{ SetPlaceHolder, ClearContent, ClearPlaceHolder }
+            << false;
+    QTest::addRow("text set + no placeholder set + empty text set")
+            << QList<SetupCommand>{ SetContent, ClearContent }
+            << false;
+    QTest::addRow("text set + empty placeholder set")
+            << QList<SetupCommand>{ SetContent, ClearPlaceHolder }
+            << false;
+    QTest::addRow("text set + placeholder set")
+            << QList<SetupCommand>{ SetContent, SetPlaceHolder }
+            << false;
+    QTest::addRow("text set + placeholder set + empty text set")
+            << QList<SetupCommand>{ SetContent, SetPlaceHolder, ClearContent }
+            << true;
+    QTest::addRow("text set + placeholder set + empty placeholder set")
+            << QList<SetupCommand>{ SetContent, SetPlaceHolder, ClearPlaceHolder }
+            << false;
+}
+
+void tst_QPlainTextEdit::placeholderVisibility()
+{
+    QFETCH(QList<SetupCommand>, setupCommands);
+    QFETCH(bool, placeholderVisible);
+
+    QPlainTextEdit plainTextEdit;
+    for (auto command : setupCommands) {
+        switch (command) {
+        case ClearPlaceHolder:
+            plainTextEdit.setPlaceholderText("");
+            break;
+        case SetPlaceHolder:
+            plainTextEdit.setPlaceholderText("Qt is awesome !");
+            break;
+        case ClearContent:
+            plainTextEdit.setPlainText("");
+            break;
+        case SetContent:
+            plainTextEdit.setPlainText("PlainText...");
+            break;
+        }
+    }
+    auto *plainTextEdit_d = static_cast<QPlainTextEditPrivate *>(qt_widget_private(&plainTextEdit));
+
+    plainTextEdit.show();
+    QVERIFY(QTest::qWaitForWindowExposed(&plainTextEdit));
+    QTRY_VERIFY(plainTextEdit_d->placeholderVisible == placeholderVisible);
+}
+
 QTEST_MAIN(tst_QPlainTextEdit)
 #include "tst_qplaintextedit.moc"