Fix updating the text cursor position after editing

In some cases when editing the text (for example when removing the
selected text, or pasting a text block) the text cursor position is
updated, but its visual x position is not updated. This causes the next
cursor movements to start from a wrong position.

Force the update for those cases.

Fixes: QTBUG-78479
Change-Id: Ia496be62beec58660f5e1695e5aafae09c79684e
Reviewed-by: Christian Ehrlicher <ch.ehrlicher@gmx.de>

src/gui/text/qtextcursor.cpp

@@ -2261,6 +2261,7 @@ void QTextCursor::insertFragment(const QTextDocumentFragment &fragment)
     d->remove();
     fragment.d->insert(*this);
     d->priv->endEditBlock();
+    d->setX();
 
     if (fragment.d && fragment.d->doc)
         d->priv->mergeCachedResources(fragment.d->doc->docHandle());

src/widgets/widgets/qwidgettextcontrol.cpp

@@ -1283,6 +1283,8 @@ void QWidgetTextControlPrivate::keyPressEvent(QKeyEvent *e)
         } else {
             QTextCursor localCursor = cursor;
             localCursor.deletePreviousChar();
+            if (cursor.d)
+                cursor.d->setX();
         }
         goto accept;
     }
@@ -1322,9 +1324,13 @@ void QWidgetTextControlPrivate::keyPressEvent(QKeyEvent *e)
     else if (e == QKeySequence::Delete) {
         QTextCursor localCursor = cursor;
         localCursor.deleteChar();
+        if (cursor.d)
+            cursor.d->setX();
     } else if (e == QKeySequence::Backspace) {
         QTextCursor localCursor = cursor;
         localCursor.deletePreviousChar();
+        if (cursor.d)
+            cursor.d->setX();
     }else if (e == QKeySequence::DeleteEndOfWord) {
         if (!cursor.hasSelection())
             cursor.movePosition(QTextCursor::NextWord, QTextCursor::KeepAnchor);

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

@@ -155,6 +155,7 @@ private slots:
 #if QT_CONFIG(scrollbar)
     void updateAfterChangeCenterOnScroll();
 #endif
+    void updateCursorPositionAfterEdit();
 
 private:
     void createSelection();
@@ -1789,5 +1790,50 @@ void tst_QPlainTextEdit::updateAfterChangeCenterOnScroll()
 
 #endif
 
+void tst_QPlainTextEdit::updateCursorPositionAfterEdit()
+{
+    QPlainTextEdit plaintextEdit;
+    plaintextEdit.setPlainText("some text some text\nsome text some text");
+
+    const auto initialPosition = 1;
+
+    // select some text
+    auto cursor = plaintextEdit.textCursor();
+    cursor.setPosition(initialPosition, QTextCursor::MoveAnchor);
+    cursor.setPosition(initialPosition + 3, QTextCursor::KeepAnchor);
+    plaintextEdit.setTextCursor(cursor);
+    QVERIFY(plaintextEdit.textCursor().hasSelection());
+
+    QTest::keyClick(&plaintextEdit, Qt::Key_Delete);
+    QTest::keyClick(&plaintextEdit, Qt::Key_Down);
+    QTest::keyClick(&plaintextEdit, Qt::Key_Up);
+
+    // Moving the cursor down and up should bring it to the initial position
+    QCOMPARE(plaintextEdit.textCursor().position(), initialPosition);
+
+    // Test the same with backspace
+    cursor = plaintextEdit.textCursor();
+    cursor.setPosition(initialPosition + 3, QTextCursor::KeepAnchor);
+    plaintextEdit.setTextCursor(cursor);
+    QVERIFY(plaintextEdit.textCursor().hasSelection());
+
+    QTest::keyClick(&plaintextEdit, Qt::Key_Backspace);
+    QTest::keyClick(&plaintextEdit, Qt::Key_Down);
+    QTest::keyClick(&plaintextEdit, Qt::Key_Up);
+
+    // Moving the cursor down and up should bring it to the initial position
+    QCOMPARE(plaintextEdit.textCursor().position(), initialPosition);
+
+    // Test insertion
+    const QString txt("txt");
+    QApplication::clipboard()->setText(txt);
+    plaintextEdit.paste();
+    QTest::keyClick(&plaintextEdit, Qt::Key_Down);
+    QTest::keyClick(&plaintextEdit, Qt::Key_Up);
+
+    // The curser should move back to the end of the copied text
+    QCOMPARE(plaintextEdit.textCursor().position(), initialPosition + txt.length());
+}
+
 QTEST_MAIN(tst_QPlainTextEdit)
 #include "tst_qplaintextedit.moc"