qquicktextinput: Fix validation for IM event

If validation did not pass after text pre-editing is finished, it need
to be roll back to state before pre-editing started.

Before this change, if validation did not pass, text was always rolled
back to previous state. In pre-editing text case, it means back to the
state in which part of the text was removed (and later changed to
pre-edited text). It may cause a situation of removing part of the text
that was already validated

Fixes: QTBUG-90239
Change-Id: I3ec39e0f6b8a93d4e6fd190af30d4c80a0e495eb
Reviewed-by: Rami Potinkara <rami.potinkara@qt.io>
Reviewed-by: Assam Boudjelthia <assam.boudjelthia@qt.io>
(cherry picked from commit b1ae151acc80254ab0ec2937c55b99223205875c)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

2 files changed, 28 insertions, 2 deletions

diff --git a/src/quick/items/qquicktextinput.cpp b/src/quick/items/qquicktextinput.cpp
index d423e6b656..faa1d5fb43 100644
--- a/src/quick/items/qquicktextinput.cpp
+++ b/src/quick/items/qquicktextinput.cpp
@@ -3471,8 +3471,12 @@ void QQuickTextInputPrivate::processInputMethodEvent(QInputMethodEvent *event)
     }
     QString oldPreeditString = m_textLayout.preeditAreaText();
     m_textLayout.setPreeditArea(m_cursor, event->preeditString());
-    if (oldPreeditString != m_textLayout.preeditAreaText())
+    if (oldPreeditString != m_textLayout.preeditAreaText()) {
         emit q->preeditTextChanged();
+        if (!event->preeditString().isEmpty() && m_undoPreeditState == -1)
+            // Pre-edit text started. Remember state for undo purpose.
+            m_undoPreeditState = priorState;
+    }
     const int oldPreeditCursor = m_preeditCursor;
     m_preeditCursor = event->preeditString().length();
     hasImState = !event->preeditString().isEmpty();
@@ -3515,6 +3519,11 @@ void QQuickTextInputPrivate::processInputMethodEvent(QInputMethodEvent *event)
         q->updateInputMethod(Qt::ImCursorRectangle | Qt::ImAnchorRectangle
                             | Qt::ImCurrentSelection);
     }
+
+    // Empty pre-edit text handled. Clean m_undoPreeditState
+    if (event->preeditString().isEmpty())
+        m_undoPreeditState = -1;
+
 }
 #endif // im
 
@@ -3591,6 +3600,12 @@ bool QQuickTextInputPrivate::finishChange(int validateFromState, bool update, bo
         if (m_maskData)
             checkIsValid();
 
+#if QT_CONFIG(im)
+        // If we were during pre-edit, validateFromState should point to the state before pre-edit
+        // has been started. Choose the correct oldest remembered state
+        if (m_undoPreeditState >= 0 && (m_undoPreeditState < validateFromState || validateFromState < 0))
+                validateFromState = m_undoPreeditState;
+#endif
         if (validateFromState >= 0 && wasValidInput && !m_validInput) {
             if (m_transactions.count())
                 return false;
@@ -3663,6 +3678,9 @@ void QQuickTextInputPrivate::internalSetText(const QString &txt, int pos, bool e
     }
     m_history.clear();
     m_undoState = 0;
+#if QT_CONFIG(im)
+    m_undoPreeditState = -1;
+#endif
     m_cursor = (pos < 0 || pos > m_text.length()) ? m_text.length() : pos;
     m_textDirty = (oldText != m_text);
 
diff --git a/src/quick/items/qquicktextinput_p_p.h b/src/quick/items/qquicktextinput_p_p.h
index cb965f2fed..b4561556aa 100644
--- a/src/quick/items/qquicktextinput_p_p.h
+++ b/src/quick/items/qquicktextinput_p_p.h
@@ -110,6 +110,7 @@ public:
         , m_cursor(0)
 #if QT_CONFIG(im)
         , m_preeditCursor(0)
+        , m_undoPreeditState(-1)
 #endif
         , m_blinkEnabled(false)
         , m_blinkTimer(0)
@@ -248,6 +249,7 @@ public:
     int m_cursor;
 #if QT_CONFIG(im)
     int m_preeditCursor;
+    int m_undoPreeditState;
 #endif
     bool m_blinkEnabled;
     int m_blinkTimer;
@@ -335,7 +337,13 @@ public:
 
     bool isUndoAvailable() const { return !m_readOnly && m_undoState; }
     bool isRedoAvailable() const { return !m_readOnly && m_undoState < (int)m_history.size(); }
-    void clearUndo() { m_history.clear(); m_undoState = 0; }
+    void clearUndo() {
+            m_history.clear();
+            m_undoState = 0;
+#if QT_CONFIG(im)
+            m_undoPreeditState = -1;
+#endif
+    }
 
     bool allSelected() const { return !m_text.isEmpty() && m_selstart == 0 && m_selend == (int)m_text.length(); }
     bool hasSelectedText() const { return !m_text.isEmpty() && m_selend > m_selstart; }