Bug 1207868 - Implement Debugger.Object.asEnvironment. (r=jimb)

js/src/doc/Debugger/Debugger.Object.md

@@ -427,9 +427,9 @@ code), the call throws a [`Debugger.DebuggeeWouldRun`][wouldrun] exception.
 
 `asEnvironment()`
 :   If the referent is a global object, return the [`Debugger.Environment`][environment]
-    instance representing the referent as a variable environment for
-    evaluating code. If the referent is not a global object, throw a
-    `TypeError`.
+    instance representing the referent's global lexical scope. The global
+    lexical scope's enclosing scope is the global object. If the referent is
+    not a global object, throw a `TypeError`.
 
 <code>setObjectWatchpoint(<i>handler</i>)</code> <i>(future plan)</i>
 :   Set a watchpoint on all the referent's own properties, reporting events

js/src/jit-test/tests/debug/Object-asEnvironment-01.js

@@ -0,0 +1,15 @@
+// Tests D.O.asEnvironment() returning the global lexical scope.
+
+var g = newGlobal();
+var dbg = new Debugger;
+var gw = dbg.addDebuggee(g);
+
+g.evaluate(`
+  var x = 42;
+  let y = "foo"
+`);
+
+var globalLexical = gw.asEnvironment();
+assertEq(globalLexical.names().length, 1);
+assertEq(globalLexical.getVariable("y"), "foo");
+assertEq(globalLexical.parent.getVariable("x"), 42);

js/src/vm/Debugger.cpp

@@ -7687,6 +7687,24 @@ DebuggerObject_executeInGlobalWithBindings(JSContext* cx, unsigned argc, Value*
                                args.rval(), dbg, globalLexical, nullptr);
 }
 
+static bool
+DebuggerObject_asEnvironment(JSContext* cx, unsigned argc, Value* vp)
+{
+    THIS_DEBUGOBJECT_OWNER_REFERENT(cx, argc, vp, "asEnvironment", args, dbg, referent);
+    if (!RequireGlobalObject(cx, args.thisv(), referent))
+        return false;
+
+    Rooted<Env*> env(cx);
+    {
+        AutoCompartment ac(cx, referent);
+        env = GetDebugScopeForGlobalLexicalScope(cx);
+        if (!env)
+            return false;
+    }
+
+    return dbg->wrapEnvironment(cx, env, args.rval());
+}
+
 static bool
 DebuggerObject_unwrap(JSContext* cx, unsigned argc, Value* vp)
 {
@@ -7764,6 +7782,7 @@ static const JSFunctionSpec DebuggerObject_methods[] = {
     JS_FN("makeDebuggeeValue", DebuggerObject_makeDebuggeeValue, 1, 0),
     JS_FN("executeInGlobal", DebuggerObject_executeInGlobal, 1, 0),
     JS_FN("executeInGlobalWithBindings", DebuggerObject_executeInGlobalWithBindings, 2, 0),
+    JS_FN("asEnvironment", DebuggerObject_asEnvironment, 0, 0),
     JS_FN("unwrap", DebuggerObject_unwrap, 0, 0),
     JS_FN("unsafeDereference", DebuggerObject_unsafeDereference, 0, 0),
     JS_FS_END

js/src/vm/ScopeObject.cpp

@@ -2859,6 +2859,13 @@ js::GetDebugScopeForFrame(JSContext* cx, AbstractFramePtr frame, jsbytecode* pc)
     return GetDebugScope(cx, si);
 }
 
+JSObject*
+js::GetDebugScopeForGlobalLexicalScope(JSContext* cx)
+{
+    ScopeIter si(cx, &cx->global()->lexicalScope(), &cx->global()->lexicalScope().staticBlock());
+    return GetDebugScope(cx, si);
+}
+
 // See declaration and documentation in jsfriendapi.h
 JS_FRIEND_API(JSObject*)
 js::GetNearestEnclosingWithScopeObjectForFunction(JSFunction* fun)

js/src/vm/ScopeObject.h

@@ -1109,13 +1109,13 @@ class LiveScopeVal
  * now incomplete: it may not contain all, or any, of the ScopeObjects to
  * represent the current scope.
  *
- * To resolve this, the debugger first calls GetDebugScopeFor(Function|Frame)
- * to synthesize a "debug scope chain". A debug scope chain is just a chain of
- * objects that fill in missing scopes and protect the engine from unexpected
- * access. (The latter means that some debugger operations, like redefining a
- * lexical binding, can fail when a true eval would succeed.) To do both of
- * these things, GetDebugScopeFor* creates a new proxy DebugScopeObject to sit
- * in front of every existing ScopeObject.
+ * To resolve this, the debugger first calls GetDebugScopeFor* to synthesize a
+ * "debug scope chain". A debug scope chain is just a chain of objects that
+ * fill in missing scopes and protect the engine from unexpected access. (The
+ * latter means that some debugger operations, like redefining a lexical
+ * binding, can fail when a true eval would succeed.) To do both of these
+ * things, GetDebugScopeFor* creates a new proxy DebugScopeObject to sit in
+ * front of every existing ScopeObject.
  *
  * GetDebugScopeFor* ensures the invariant that the same DebugScopeObject is
  * always produced for the same underlying scope (optimized or not!). This is
@@ -1128,6 +1128,9 @@ GetDebugScopeForFunction(JSContext* cx, HandleFunction fun);
 extern JSObject*
 GetDebugScopeForFrame(JSContext* cx, AbstractFramePtr frame, jsbytecode* pc);
 
+extern JSObject*
+GetDebugScopeForGlobalLexicalScope(JSContext* cx);
+
 /* Provides debugger access to a scope. */
 class DebugScopeObject : public ProxyObject
 {