make QScriptEngine::setGlobalObject() work to some extent

JSC requires that the global object is actually a
JSGlobalObject instance, whereas QScriptEngine::setGlobalObject()
allows any object to be set as the global object. The way we
solve this is by proxying from an internal global object to the
custom (user-set) object.

We need to take care that the internal global object is never
actually exposed through our API; a brilliantly named helper
function, toUsableValue(), makes that happen.

Evaluating "var a = 10" with a custom global object doesn't work
yet; the variable always ends up in the internal Global Object.
For variable assignments, JSC appears to bypass the normal
JSObject::put() and instead use
JSGlobalObject::copyGlobals{From,To}(), which means I can't
intercept and proxy the assignments.

This commit enough to get the Context2D example working. There's
another bug with iteration of the built-in Global Object's
properties (non-enumerable properties are always skipped by the
JSC C++ API, whereas with QScriptValueIterator they should not
be), but that's a totally separate issue.

1 files changed, 7 insertions, 2 deletions

diff --git a/src/script/api/qscriptengine_p.h b/src/script/api/qscriptengine_p.h
index 4db77c0..c0f5e13 100644
--- a/src/script/api/qscriptengine_p.h
+++ b/src/script/api/qscriptengine_p.h
@@ -110,8 +110,13 @@ public:
     QScriptContext *contextForFrame(JSC::ExecState *frame);
     void releaseContextForFrame(JSC::ExecState *frame);
 
-    JSC::JSGlobalObject *globalObject() const;
+    JSC::JSGlobalObject *originalGlobalObject() const;
+    JSC::JSObject *getOriginalGlobalObjectProxy();
+    JSC::JSObject *customGlobalObject() const;
+    JSC::JSObject *globalObject() const;
+    void setGlobalObject(JSC::JSObject *object);
     JSC::ExecState *globalExec() const;
+    JSC::JSValue toUsableValue(JSC::JSValue value);
 
     void mark();
     bool isCollecting() const;
@@ -162,7 +167,7 @@ public:
 #endif
 
     JSC::JSGlobalData *globalData;
-    JSC::JSObject *customGlobalObject;
+    JSC::JSObject *originalGlobalObjectProxy;
     JSC::ExecState *currentFrame;
     QHash<JSC::ExecState*, QScriptContext*> contextForFrameHash;