QSyntaxHighlighter: Fix crash when parent is a nullptr

QSyntaxHighlighter has the follwoing constructor taking a QObject

  QSyntaxHighlighter::QSyntaxHighlighter(QObject *parent)
    : QObject(*new QSyntaxHighlighterPrivate, parent)
  {
      if (parent->inherits("QTextEdit")) {
          // ...
      }
  }

Typically, a 'parent' refers to the parent/child hierarchy in Qt
and is allowed to be a nullptr. However, in this case, passing a
nullptr will lead to a crash, as reported in
https://bugs.kde.org/show_bug.cgi?id=404820

This patch makes the QSyntaxHighlighter constructor nullptr safe
by checking if parent is a valid pointer.

Change-Id: Ia4e9b46b94fd37e6ceb2cd0538594353fdc1e349
Reviewed-by: Jesus Fernandez <Jesus.Fernandez@qt.io>
Reviewed-by: Christoph Cullmann <cullmann@kde.org>

1 files changed, 1 insertions, 1 deletions

diff --git a/src/gui/text/qsyntaxhighlighter.cpp b/src/gui/text/qsyntaxhighlighter.cpp
index 0e07b69868..102a776ed3 100644
--- a/src/gui/text/qsyntaxhighlighter.cpp
+++ b/src/gui/text/qsyntaxhighlighter.cpp
@@ -297,7 +297,7 @@ void QSyntaxHighlighterPrivate::reformatBlock(const QTextBlock &block)
 QSyntaxHighlighter::QSyntaxHighlighter(QObject *parent)
     : QObject(*new QSyntaxHighlighterPrivate, parent)
 {
-    if (parent->inherits("QTextEdit")) {
+    if (parent && parent->inherits("QTextEdit")) {
         QTextDocument *doc = parent->property("document").value<QTextDocument *>();
         if (doc)
             setDocument(doc);