Revert "TextEditor: Use synchronous highlighter by default"

This reverts commit 1c47a0a301c291b0ec450b7a141c5067d402dac4.
Changing the default revealed a crash that seem to be caused by the
async syntax highlighter infra structure changes. Revert the default for
now to figure out the cause of the crash.

Task-number: QTCREATORBUG-30494
Change-Id: I1d0388c29d206cb25f2d58e4b305aa8303db2a60
Reviewed-by: Robert Löhning <robert.loehning@qt.io>
Reviewed-by: <github-actions-qt-creator@cristianadam.eu>
Reviewed-by: Eike Ziller <eike.ziller@qt.io>

2 files changed, 7 insertions, 11 deletions

diff --git a/src/plugins/texteditor/textdocument.cpp b/src/plugins/texteditor/textdocument.cpp
index 2636ad46e2..cb421f2bf7 100644
--- a/src/plugins/texteditor/textdocument.cpp
+++ b/src/plugins/texteditor/textdocument.cpp
@@ -914,23 +914,19 @@ bool TextDocument::reload(QString *errorString, ReloadFlag flag, ChangeType type
 void TextDocument::resetSyntaxHighlighter(const std::function<SyntaxHighlighter *()> &creator,
                                           bool threaded)
 {
-    delete d->m_highlighterRunner;
+    if (d->m_highlighterRunner)
+        delete d->m_highlighterRunner;
 
-    static const std::optional<bool> envValue = []() -> std::optional<bool> {
-        const QString key("QTC_USE_THREADED_HIGHLIGHTER");
-        if (qtcEnvironmentVariableIsSet(key)) {
-            const QString value = qtcEnvironmentVariable(key).toUpper();
-            return value != "FALSE" && value != "0";
-        }
-        return {};
-    }();
+    static const bool envValue
+        = qtcEnvironmentVariable("QTC_USE_THREADED_HIGHLIGHTER", "TRUE").toUpper()
+          == QLatin1String("TRUE");
 
     SyntaxHighlighter *highlighter = creator();
     highlighter->setFontSettings(TextEditorSettings::fontSettings());
     highlighter->setMimeType(mimeType());
     d->m_highlighterRunner = new SyntaxHighlighterRunner(highlighter,
                                                          document(),
-                                                         envValue.value_or(threaded));
+                                                         threaded && envValue);
 }
 
 void TextDocument::cleanWhitespace(const QTextCursor &cursor)
diff --git a/src/plugins/texteditor/textdocument.h b/src/plugins/texteditor/textdocument.h
index 5879d9e9ec..ad3fe262e2 100644
--- a/src/plugins/texteditor/textdocument.h
+++ b/src/plugins/texteditor/textdocument.h
@@ -127,7 +127,7 @@ public:
     QTextDocument *document() const;
 
     using SyntaxHighLighterCreator = std::function<SyntaxHighlighter *()>;
-    void resetSyntaxHighlighter(const SyntaxHighLighterCreator &creator, bool threaded = false);
+    void resetSyntaxHighlighter(const SyntaxHighLighterCreator &creator, bool threaded = true);
     SyntaxHighlighterRunner *syntaxHighlighterRunner() const;
 
     bool reload(QString *errorString, QTextCodec *codec);