QmlCompiler: Drop broken line comments in generated C++

They didn't work because the ordering of instructions is not the same as
the ordering of lines. They also weren't very helpful because a single
line may result in multiple instructions and vice versa. On top of
everything, they also introduced UB via the std::upper_bound call.

Rather, just print the name of the function and the place in the file at
the beginning of each C++ function. That is much more helpful since we
can then just correlate it to the original QML code. For
instruction-by-instruction mapping we have to consult the byte code
trace anyway.

Pick-to: 6.5 6.4 6.2
Fixes: QTBUG-111340
Change-Id: I599ce384cfaf88a7347583a55976a3b98080435d
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>

src/qmlcompiler/qqmljscodegenerator.cpp

@@ -56,9 +56,8 @@ QString QQmlJSCodeGenerator::castTargetName(const QQmlJSScope::ConstPtr &type) c
 QQmlJSCodeGenerator::QQmlJSCodeGenerator(const QV4::Compiler::Context *compilerContext,
         const QV4::Compiler::JSUnitGenerator *unitGenerator,
         const QQmlJSTypeResolver *typeResolver,
-        QQmlJSLogger *logger, const QStringList &sourceCodeLines)
+        QQmlJSLogger *logger)
     : QQmlJSCompilePass(unitGenerator, typeResolver, logger)
-    , m_sourceCodeLines(sourceCodeLines)
     , m_context(compilerContext)
 {}
 
@@ -141,6 +140,9 @@ QT_WARNING_POP
     QQmlJSAotFunction result;
     result.includes.swap(m_includes);
 
+    result.code += u"// %1 at line %2, column %3\n"_s
+            .arg(m_context->name).arg(m_context->line).arg(m_context->column);
+
     QDuplicateTracker<QString> generatedVariables;
     for (auto registerIt = m_registerVariables.cbegin(), registerEnd = m_registerVariables.cend();
          registerIt != registerEnd; ++registerIt) {
@@ -2585,17 +2587,6 @@ QV4::Moth::ByteCodeHandler::Verdict QQmlJSCodeGenerator::startInstruction(
              || !m_state.accumulatorVariableOut.isEmpty()
              || !isTypeStorable(m_typeResolver, m_state.changedRegister().storedType()));
 
-    const int currentLine = currentSourceLocation().startLine;
-    if (currentLine != m_lastLineNumberUsed) {
-        const int nextLine = nextJSLine(currentLine);
-        for (auto line = currentLine - 1; line < nextLine - 1; ++line) {
-            m_body += u"// "_s;
-            m_body += m_sourceCodeLines.value(line).trimmed();
-            m_body += u'\n';
-        }
-        m_lastLineNumberUsed = currentLine;
-    }
-
     // If the instruction has no side effects and doesn't write any register, it's dead.
     // We might still need the label, though, and the source code comment.
     if (!m_state.hasSideEffects() && changedRegisterVariable().isEmpty())
@@ -3193,21 +3184,6 @@ QString QQmlJSCodeGenerator::conversion(const QQmlJSScope::ConstPtr &from,
     return QString();
 }
 
-int QQmlJSCodeGenerator::nextJSLine(uint line) const
-{
-    auto findLine = [](int line, const QV4::CompiledData::CodeOffsetToLineAndStatement &entry) {
-        return entry.line > line;
-    };
-    const auto codeToLine
-        = std::upper_bound(m_context->lineAndStatementNumberMapping.constBegin(),
-                           m_context->lineAndStatementNumberMapping.constEnd(),
-                           line,
-                           findLine);
-    bool bNoNextLine = m_context->lineAndStatementNumberMapping.constEnd() == codeToLine;
-
-    return static_cast<int>(bNoNextLine ? -1 : codeToLine->line);
-}
-
 void QQmlJSCodeGenerator::reject(const QString &thing)
 {
     setError(u"Cannot generate efficient code for %1"_s.arg(thing));

src/qmlcompiler/qqmljscodegenerator_p.h

@@ -33,7 +33,7 @@ public:
     QQmlJSCodeGenerator(const QV4::Compiler::Context *compilerContext,
                        const QV4::Compiler::JSUnitGenerator *unitGenerator,
                        const QQmlJSTypeResolver *typeResolver,
-                       QQmlJSLogger *logger, const QStringList &sourceCodeLines);
+                       QQmlJSLogger *logger);
     ~QQmlJSCodeGenerator() = default;
 
     QQmlJSAotFunction run(const Function *function, const InstructionAnnotations *annotations,
@@ -288,17 +288,12 @@ private:
         return m_typeResolver->jsGlobalObject()->property(u"console"_s).type();
     }
 
-    int nextJSLine(uint line) const;
-
-    QStringList m_sourceCodeLines;
-
     // map from instruction offset to sequential label number
     QHash<int, QString> m_labels;
 
     const QV4::Compiler::Context *m_context = nullptr;
     const InstructionAnnotations *m_annotations = nullptr;
 
-    int m_lastLineNumberUsed = -1;
     bool m_skipUntilNextLabel = false;
 
     QStringList m_includes;

src/qmlcompiler/qqmljscompiler.cpp

@@ -650,7 +650,6 @@ void QQmlJSAotCompiler::setDocument(
     m_logger->setFileName(resourcePathInfo.fileName());
     m_logger->setCode(irDocument->code);
     m_unitGenerator = &irDocument->jsGenerator;
-    m_entireSourceCodeLines = irDocument->code.split(u'\n');
     QQmlJSScope::Ptr target = QQmlJSScope::create();
     QQmlJSImportVisitor visitor(target, m_importer, m_logger,
                                 resourcePathInfo.canonicalPath() + u'/',
@@ -796,8 +795,7 @@ QQmlJSAotFunction QQmlJSAotCompiler::doCompile(
         return compileError();
 
     QQmlJSCodeGenerator codegen(
-                context, m_unitGenerator, &m_typeResolver, m_logger,
-                m_entireSourceCodeLines);
+                context, m_unitGenerator, &m_typeResolver, m_logger);
     QQmlJSAotFunction result = codegen.run(function, &typePropagationResult, error);
     return error->isValid() ? compileError() : result;
 }

src/qmlcompiler/qqmljscompiler_p.h

@@ -76,7 +76,6 @@ protected:
             const QString &message, QtMsgType type, const QQmlJS::SourceLocation &location) const;
 
     QQmlJSTypeResolver m_typeResolver;
-    QStringList m_entireSourceCodeLines;
 
     const QString m_resourcePath;
     const QStringList m_qmldirFiles;

src/qmlcompiler/qqmljslintercodegen.cpp

@@ -27,7 +27,6 @@ void QQmlJSLinterCodegen::setDocument(const QmlIR::JSCodeGen *codegen,
     Q_UNUSED(codegen);
     m_document = document;
     m_unitGenerator = &document->jsGenerator;
-    m_entireSourceCodeLines = document->code.split(u'\n');
 }
 
 std::variant<QQmlJSAotFunction, QQmlJS::DiagnosticMessage>