Clean up JSCallData setup

We either have pre-populated arguments and thisObject, then we can just
use them and keep them const. Or, we want to allocate and populate the
arguments and the thisObject. Then, do allocate them in a separate
object, and transform that into JSCallData afterwards if necessary.

Furthermore, avoid alloc(0) as that just returns the current stack top.
Writing to it will clobber other data. Rather, just use nullptr and
crash if it's written to.

Also, remove the useless operator-> from JSCallData. That one just
confuses the reader.

Change-Id: I8310911fcfe005b05a07b78fcb3791d991a0c2ce
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>

1 files changed, 47 insertions, 25 deletions

diff --git a/src/qml/jsruntime/qv4jscall_p.h b/src/qml/jsruntime/qv4jscall_p.h
index 43dc0de727..15ede20be3 100644
--- a/src/qml/jsruntime/qv4jscall_p.h
+++ b/src/qml/jsruntime/qv4jscall_p.h
@@ -61,39 +61,61 @@ QT_BEGIN_NAMESPACE
 
 namespace QV4 {
 
-struct JSCallData {
-    JSCallData(const Value *thisObject, const Value *argv, int argc)
-        : argc(argc), args(const_cast<Value *>(argv)), thisObject(const_cast<Value *>(thisObject))
+template<typename Args>
+CallData *callDatafromJS(const Scope &scope, const Args *args, const FunctionObject *f = nullptr)
+{
+    int size = int(offsetof(QV4::CallData, args)/sizeof(QV4::Value)) + args->argc;
+    CallData *ptr = reinterpret_cast<CallData *>(scope.alloc<Scope::Uninitialized>(size));
+    ptr->function = Encode::undefined();
+    ptr->context = Encode::undefined();
+    ptr->accumulator = Encode::undefined();
+    ptr->thisObject = args->thisObject ? args->thisObject->asReturnedValue() : Encode::undefined();
+    ptr->newTarget = Encode::undefined();
+    ptr->setArgc(args->argc);
+    if (args->argc)
+        memcpy(ptr->args, args->args, args->argc*sizeof(Value));
+    if (f)
+        ptr->function = f->asReturnedValue();
+    return ptr;
+}
+
+struct JSCallArguments
+{
+    JSCallArguments(const Scope &scope, int argc = 0)
+        : thisObject(scope.alloc()), args(scope.alloc(argc)), argc(argc)
     {
     }
 
-    JSCallData(const Scope &scope, int argc = 0)
-        : argc(argc), args(scope.alloc(argc)), thisObject(scope.alloc())
+    CallData *callData(const Scope &scope, const FunctionObject *f = nullptr) const
     {
+        return callDatafromJS(scope, this, f);
     }
 
-    JSCallData *operator->() {
-        return this;
+    Value *thisObject;
+    Value *args;
+    const int argc;
+};
+
+struct JSCallData
+{
+    JSCallData(const Value *thisObject, const Value *argv, int argc)
+        : thisObject(thisObject), args(argv), argc(argc)
+    {
     }
 
-    CallData *callData(const Scope &scope, const FunctionObject *f = nullptr) const {
-        int size = int(offsetof(QV4::CallData, args)/sizeof(QV4::Value)) + argc;
-        CallData *ptr = reinterpret_cast<CallData *>(scope.alloc<Scope::Uninitialized>(size));
-        ptr->function = Encode::undefined();
-        ptr->context = Encode::undefined();
-        ptr->accumulator = Encode::undefined();
-        ptr->thisObject = thisObject ? thisObject->asReturnedValue() : Encode::undefined();
-        ptr->newTarget = Encode::undefined();
-        ptr->setArgc(argc);
-        if (argc)
-            memcpy(ptr->args, args, argc*sizeof(Value));
-        if (f)
-            ptr->function = f->asReturnedValue();
-        return ptr;
+    Q_IMPLICIT JSCallData(const JSCallArguments &args)
+        : thisObject(args.thisObject), args(args.args), argc(args.argc)
+    {
     }
-    int argc;
-    Value *args;
-    Value *thisObject;
+
+    CallData *callData(const Scope &scope, const FunctionObject *f = nullptr) const
+    {
+        return callDatafromJS(scope, this, f);
+    }
+
+    const Value *thisObject;
+    const Value *args;
+    const int argc;
 };
 
 inline
@@ -108,7 +130,7 @@ ReturnedValue FunctionObject::call(const JSCallData &data) const
     return call(data.thisObject, data.args, data.argc);
 }
 
-void populateJSCallArguments(ExecutionEngine *v4, JSCallData &jsCall, int argc,
+void populateJSCallArguments(ExecutionEngine *v4, JSCallArguments &jsCall, int argc,
                              void **args, const QMetaType *types);
 
 struct ScopedStackFrame {