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, 5 insertions, 4 deletions

diff --git a/src/script/api/qscriptvalue.cpp b/src/script/api/qscriptvalue.cpp
index 5ace14d..59e6729 100644
--- a/src/script/api/qscriptvalue.cpp
+++ b/src/script/api/qscriptvalue.cpp
@@ -276,19 +276,20 @@ QScriptValuePrivate::QScriptValueAutoRegister& QScriptValuePrivate::QScriptValue
     return *this;
 };
 
-
 void QScriptValuePrivate::initFromJSCValue(JSC::JSValue value)
 {
-    type = JSC;
-    jscValue = value;
     if (value.isCell()) {
-        JSC::JSCell *cell = value.asCell();
         Q_ASSERT(engine != 0);
         QScriptEnginePrivate *eng_p = QScriptEnginePrivate::get(engine);
+        value = eng_p->toUsableValue(value);
+        JSC::JSCell *cell = JSC::asCell(value);
+        Q_ASSERT(cell != eng_p->originalGlobalObject());
         if (!eng_p->keepAliveValues.contains(cell))
             eng_p->keepAliveValues[cell] = 0;
         eng_p->keepAliveValues[cell].ref();
     }
+    type = JSC;
+    jscValue = value;
 }
 
 void QScriptValuePrivate::initFromNumber(double value)