Q(Plain)TextEdit: don't crash when using a style sheet

When using a style sheet, Q(Plain)TextEdit::isReadOnly() might get
called during the initialization before d->control is properly
initialized which lead to a crash.
This amends 43ce457cbd093fc06d99b5ac833c789ef7c893d5.

Fixes: QTBUG-121697
Fixes: QTBUG-121790
Task-number: QTBUG-1857
Change-Id: I15c357c9eef7f6559bcc2ad89033a3d8e7fcbfef
Reviewed-by: David Faure <david.faure@kdab.com>
(cherry picked from commit c6af5b9c12e1ea4cec007c5efe869636ce97a9d2)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>
(cherry picked from commit e9b187a836974f05ba8f42eb72854a5effdc6c15)
(cherry picked from commit ff1f12d5a0f57143e0e3c8d781bb3fdc884af7bc)

4 files changed, 23 insertions, 2 deletions

diff --git a/src/widgets/widgets/qplaintextedit.cpp b/src/widgets/widgets/qplaintextedit.cpp
index 134fc30964..087b7e4d21 100644
--- a/src/widgets/widgets/qplaintextedit.cpp
+++ b/src/widgets/widgets/qplaintextedit.cpp
@@ -2600,7 +2600,7 @@ void QPlainTextEdit::insertFromMimeData(const QMimeData *source)
 bool QPlainTextEdit::isReadOnly() const
 {
     Q_D(const QPlainTextEdit);
-    return !(d->control->textInteractionFlags() & Qt::TextEditable);
+    return !d->control || !(d->control->textInteractionFlags() & Qt::TextEditable);
 }
 
 void QPlainTextEdit::setReadOnly(bool ro)
diff --git a/src/widgets/widgets/qtextedit.cpp b/src/widgets/widgets/qtextedit.cpp
index d403ba73d1..b0f14cfa75 100644
--- a/src/widgets/widgets/qtextedit.cpp
+++ b/src/widgets/widgets/qtextedit.cpp
@@ -2213,7 +2213,7 @@ void QTextEdit::insertFromMimeData(const QMimeData *source)
 bool QTextEdit::isReadOnly() const
 {
     Q_D(const QTextEdit);
-    return !(d->control->textInteractionFlags() & Qt::TextEditable);
+    return !d->control || !(d->control->textInteractionFlags() & Qt::TextEditable);
 }
 
 void QTextEdit::setReadOnly(bool ro)
diff --git a/tests/auto/widgets/widgets/qplaintextedit/tst_qplaintextedit.cpp b/tests/auto/widgets/widgets/qplaintextedit/tst_qplaintextedit.cpp
index 3a1d414376..e5a700298f 100644
--- a/tests/auto/widgets/widgets/qplaintextedit/tst_qplaintextedit.cpp
+++ b/tests/auto/widgets/widgets/qplaintextedit/tst_qplaintextedit.cpp
@@ -133,6 +133,7 @@ private slots:
     void placeholderVisibility_data();
     void placeholderVisibility();
     void scrollBarSignals();
+    void dontCrashWithCss();
 
 private:
     void createSelection();
@@ -1944,5 +1945,14 @@ void tst_QPlainTextEdit::scrollBarSignals()
     QTRY_COMPARE(spy.count(), 5);
 }
 
+void tst_QPlainTextEdit::dontCrashWithCss()
+{
+    qApp->setStyleSheet("QWidget { font: 10pt; }");
+    QPlainTextEdit edit;
+    edit.show();
+    qApp->setStyleSheet(QString());
+}
+
+
 QTEST_MAIN(tst_QPlainTextEdit)
 #include "tst_qplaintextedit.moc"
diff --git a/tests/auto/widgets/widgets/qtextedit/tst_qtextedit.cpp b/tests/auto/widgets/widgets/qtextedit/tst_qtextedit.cpp
index 47e85cd839..ef9b0703b7 100644
--- a/tests/auto/widgets/widgets/qtextedit/tst_qtextedit.cpp
+++ b/tests/auto/widgets/widgets/qtextedit/tst_qtextedit.cpp
@@ -198,6 +198,8 @@ private slots:
     void nextFormatAfterEnterPressed_data();
     void nextFormatAfterEnterPressed();
 
+    void dontCrashWithCss();
+
 private:
     void createSelection();
     int blockCount() const;
@@ -3064,5 +3066,14 @@ void tst_QTextEdit::nextFormatAfterEnterPressed()
         QCOMPARE(prevBlockCursor.charFormat().property(it.key()), it.value());
 }
 
+void tst_QTextEdit::dontCrashWithCss()
+{
+    qApp->setStyleSheet("QWidget { font: 10pt; }");
+    QTextEdit edit;
+    edit.show();
+    qApp->setStyleSheet(QString());
+}
+
+
 QTEST_MAIN(tst_QTextEdit)
 #include "tst_qtextedit.moc"