Fix leak of compiler contexts

Repeatedly entering a context that was entered before would result in
leaking the previously entered context. This can happen when compiling
child objects in a QML file, which is done recursively. So before
compiling the bindings/function in the child object, first the global
context and then the QML context are entered.

The fix is to re-use the global context, as it's the same anyway for all
objects in the same module. And we can remove entering the QML context,
because nothing is in there, and we don't put anything in it ever.

Change-Id: Ib1c4259d2dec22df46e96edb65bc3d377e52e671
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>

4 files changed, 21 insertions, 13 deletions

diff --git a/src/qml/compiler/qqmlirbuilder.cpp b/src/qml/compiler/qqmlirbuilder.cpp
index a9d86b24f5..4a1b27d7aa 100644
--- a/src/qml/compiler/qqmlirbuilder.cpp
+++ b/src/qml/compiler/qqmlirbuilder.cpp
@@ -1809,8 +1809,7 @@ QVector<int> JSCodeGen::generateJSCodeForFunctionsAndBindings(const QList<Compil
     QVector<int> runtimeFunctionIndices(functions.size());
 
     QV4::Compiler::ScanFunctions scan(this, sourceCode, QV4::Compiler::GlobalCode);
-    scan.enterEnvironment(nullptr, QV4::Compiler::QmlBinding);
-    scan.enterQmlScope(qmlRoot, QStringLiteral("context scope"));
+    scan.enterGlobalEnvironment(QV4::Compiler::QmlBinding);
     for (const CompiledFunctionOrExpression &f : functions) {
         Q_ASSERT(f.node != qmlRoot);
         QQmlJS::AST::FunctionDeclaration *function = QQmlJS::AST::cast<QQmlJS::AST::FunctionDeclaration*>(f.node);
@@ -1824,7 +1823,6 @@ QVector<int> JSCodeGen::generateJSCodeForFunctionsAndBindings(const QList<Compil
         scan.leaveEnvironment();
     }
     scan.leaveEnvironment();
-    scan.leaveEnvironment();
 
     _context = nullptr;
 
diff --git a/src/qml/compiler/qv4compilercontext.cpp b/src/qml/compiler/qv4compilercontext.cpp
index 3293dc53c8..0a9d3d8efe 100644
--- a/src/qml/compiler/qv4compilercontext.cpp
+++ b/src/qml/compiler/qv4compilercontext.cpp
@@ -49,6 +49,8 @@ QT_BEGIN_NAMESPACE
 
 Context *Module::newContext(Node *node, Context *parent, CompilationMode compilationMode)
 {
+    Q_ASSERT(!contextMap.contains(node));
+
     Context *c = new Context(parent, compilationMode);
     if (node) {
         SourceLocation loc = node->firstSourceLocation();
diff --git a/src/qml/compiler/qv4compilerscanfunctions.cpp b/src/qml/compiler/qv4compilerscanfunctions.cpp
index 89f602b409..92df98f201 100644
--- a/src/qml/compiler/qv4compilerscanfunctions.cpp
+++ b/src/qml/compiler/qv4compilerscanfunctions.cpp
@@ -73,13 +73,20 @@ void ScanFunctions::operator()(Node *node)
     calcEscapingVariables();
 }
 
+void ScanFunctions::enterGlobalEnvironment(CompilationMode compilationMode)
+{
+    enterEnvironment(astNodeForGlobalEnvironment, compilationMode);
+}
+
 void ScanFunctions::enterEnvironment(Node *node, CompilationMode compilationMode)
 {
-    Context *e = _cg->_module->newContext(node, _context, compilationMode);
-    if (!e->isStrict)
-        e->isStrict = _cg->_strictMode;
-    _contextStack.append(e);
-    _context = e;
+    Context *c = _cg->_module->contextMap.value(node);
+    if (!c)
+        c = _cg->_module->newContext(node, _context, compilationMode);
+    if (!c->isStrict)
+        c->isStrict = _cg->_strictMode;
+    _contextStack.append(c);
+    _context = c;
 }
 
 void ScanFunctions::leaveEnvironment()
@@ -440,7 +447,7 @@ void ScanFunctions::calcEscapingVariables()
 {
     Module *m = _cg->_module;
 
-    for (Context *inner : m->contextMap) {
+    for (Context *inner : qAsConst(m->contextMap)) {
         for (const QString &var : qAsConst(inner->usedVariables)) {
             Context *c = inner;
             while (c) {
@@ -468,7 +475,7 @@ void ScanFunctions::calcEscapingVariables()
     static const bool showEscapingVars = qEnvironmentVariableIsSet("QV4_SHOW_ESCAPING_VARS");
     if (showEscapingVars) {
         qDebug() << "==== escaping variables ====";
-        for (Context *c : m->contextMap) {
+        for (Context *c : qAsConst(m->contextMap)) {
             qDebug() << "Context" << c->name << ":";
             qDebug() << "    Arguments escape" << c->argumentsCanEscape;
             for (auto it = c->members.constBegin(); it != c->members.constEnd(); ++it) {
diff --git a/src/qml/compiler/qv4compilerscanfunctions_p.h b/src/qml/compiler/qv4compilerscanfunctions_p.h
index 745e9f8a73..87b7210879 100644
--- a/src/qml/compiler/qv4compilerscanfunctions_p.h
+++ b/src/qml/compiler/qv4compilerscanfunctions_p.h
@@ -84,12 +84,10 @@ public:
     ScanFunctions(Codegen *cg, const QString &sourceCode, CompilationMode defaultProgramMode);
     void operator()(AST::Node *node);
 
+    void enterGlobalEnvironment(CompilationMode compilationMode);
     void enterEnvironment(AST::Node *node, CompilationMode compilationMode);
     void leaveEnvironment();
 
-    void enterQmlScope(AST::Node *ast, const QString &name)
-    { enterFunction(ast, name, /*formals*/nullptr, /*body*/nullptr, /*expr*/nullptr); }
-
     void enterQmlFunction(AST::FunctionDeclaration *ast)
     { enterFunction(ast, false); }
 
@@ -149,6 +147,9 @@ protected:
 
     bool _allowFuncDecls;
     CompilationMode defaultProgramMode;
+
+private:
+    static constexpr AST::Node *astNodeForGlobalEnvironment = nullptr;
 };
 
 }