CppEditor: Fix parentheses mismatch on comment followed by backslash

Apparently, it was mistakenly assumed that a non-zero lexer state
implies that the comment continues on the next line when it can also
mean that the line ends in a backslash. Adapt the check accordingly.

Fixes: QTCREATORBUG-29339
Change-Id: Ib239aca86dae9983d920f7715ae628ab4bf80220
Reviewed-by: David Schulz <david.schulz@qt.io>
Reviewed-by: <github-actions-qt-creator@cristianadam.eu>

src/plugins/cppeditor/cpphighlighter.cpp

@@ -56,7 +56,8 @@ void CppHighlighter::highlightBlock(const QString &text)
     const Tokens tokens = tokenize(text, initialLexerState);
     lexerState = tokenize.state(); // refresh lexer state
 
-    initialLexerState &= ~0x80; // discard newline expected bit
+    static const auto lexerStateWithoutNewLineExpectedBit = [](int state) { return state & ~0x80; };
+    initialLexerState = lexerStateWithoutNewLineExpectedBit(initialLexerState);
     int foldingIndent = initialBraceDepth;
     if (TextBlockUserData *userData = TextDocumentLayout::textUserData(currentBlock())) {
         userData->setFoldingIndent(0);
@@ -220,7 +221,8 @@ void CppHighlighter::highlightBlock(const QString &text)
     if (text.length() > lastTokenEnd)
         formatSpaces(text, lastTokenEnd, text.length() - lastTokenEnd);
 
-    if (!initialLexerState && lexerState && !tokens.isEmpty()) {
+    if (!initialLexerState && lexerStateWithoutNewLineExpectedBit(lexerState)
+        && !tokens.isEmpty()) {
         const Token &lastToken = tokens.last();
         if (lastToken.is(T_COMMENT) || lastToken.is(T_DOXY_COMMENT)) {
             insertParen({Parenthesis::Opened, QLatin1Char('+'), lastToken.utf16charsBegin()});
@@ -636,6 +638,30 @@ void CppHighlighterTest::test()
         QCOMPARE(actualFormat, expectedFormat);
     }
 }
+
+void CppHighlighterTest::testParentheses_data()
+{
+    QTest::addColumn<int>("line");
+    QTest::addColumn<int>("expectedParenCount");
+
+    QTest::newRow("function head") << 41 << 2;
+    QTest::newRow("function opening brace") << 42 << 1;
+    QTest::newRow("loop head") << 43 << 1;
+    QTest::newRow("comment") << 44 << 0;
+    QTest::newRow("loop end") << 45 << 3;
+    QTest::newRow("function closing brace") << 46 << 1;
+}
+
+void CppHighlighterTest::testParentheses()
+{
+    QFETCH(int, line);
+    QFETCH(int, expectedParenCount);
+
+    QTextBlock block = m_doc.findBlockByNumber(line - 1);
+    QVERIFY(block.isValid());
+    QCOMPARE(TextDocumentLayout::parentheses(block).count(), expectedParenCount);
+}
+
 } // namespace Internal
 #endif // WITH_TESTS
 

src/plugins/cppeditor/cpphighlighter.h

@@ -52,6 +52,8 @@ public:
 private slots:
     void test_data();
     void test();
+    void testParentheses_data();
+    void testParentheses();
 
 private:
     QTextDocument m_doc;

src/plugins/cppeditor/testcases/highlightingtestcase.cpp

@@ -37,3 +37,10 @@ const auto s5 = uR"("o
      ne")"_w;
 const auto s6 = u"o\
 ne"_w;
+
+static void parenTest()
+{
+    do {
+        /* comment */ \
+    } while (false);
+}