Bug 963879 - Part 3: Add Debugger.Environment.prototype.optimizedOut. (r=jimb)

js/src/doc/Debugger/Debugger.Environment.md

@@ -94,6 +94,12 @@ properties from its prototype:
     [`Debugger.Object`][object] instance referring to <i>f</i>. Otherwise,
     this property's value is `null`.
 
+`optimizedOut`
+:   True if this environment is optimized out. False otherwise. For example,
+    functions whose locals are never aliased may present optimized-out
+    environments. When true, `getVariable` returns an ordinary JavaScript
+    object whose `optimizedOut` property is true on all bindings, and
+    `setVariable` throws a `ReferenceError`.
 
 
 ## Function Properties of the Debugger.Environment Prototype Object

js/src/vm/Debugger.cpp

@@ -7259,6 +7259,22 @@ DebuggerEnv_getInspectable(JSContext *cx, unsigned argc, Value *vp)
     return true;
 }
 
+static bool
+DebuggerEnv_getOptimizedOut(JSContext *cx, unsigned argc, Value *vp)
+{
+    CallArgs args = CallArgsFromVp(argc, vp);
+    NativeObject *envobj = DebuggerEnv_checkThis(cx, args, "get optimizedOut", false);
+    if (!envobj)
+        return false;
+    Rooted<Env*> env(cx, static_cast<Env *>(envobj->getPrivate()));
+    MOZ_ASSERT(env);
+    MOZ_ASSERT(!env->is<ScopeObject>());
+
+    args.rval().setBoolean(env->is<DebugScopeObject>() &&
+                           env->as<DebugScopeObject>().isOptimizedOut());
+    return true;
+}
+
 static bool
 DebuggerEnv_names(JSContext *cx, unsigned argc, Value *vp)
 {
@@ -7404,6 +7420,7 @@ static const JSPropertySpec DebuggerEnv_properties[] = {
     JS_PSG("parent", DebuggerEnv_getParent, 0),
     JS_PSG("callee", DebuggerEnv_getCallee, 0),
     JS_PSG("inspectable", DebuggerEnv_getInspectable, 0),
+    JS_PSG("optimizedOut", DebuggerEnv_getOptimizedOut, 0),
     JS_PS_END
 };