Bug 1134865 - Part 1: Add JSObject::constructorDisplayAtom; r=djvj

js/src/builtin/TestingFunctions.cpp

@@ -2554,6 +2554,32 @@ SetDiscardSource(JSContext* cx, unsigned argc, Value* vp)
     return true;
 }
 
+static bool
+GetConstructorName(JSContext* cx, unsigned argc, Value* vp)
+{
+    CallArgs args = CallArgsFromVp(argc, vp);
+    if (!args.requireAtLeast(cx, "getConstructorName", 1))
+        return false;
+
+    if (!args[0].isObject()) {
+        JS_ReportErrorNumber(cx, GetErrorMessage, nullptr, JSMSG_NOT_EXPECTED_TYPE,
+                             "getConstructorName", "Object",
+                             InformalValueTypeName(args[0]));
+        return false;
+    }
+
+    RootedAtom name(cx);
+    if (!args[0].toObject().constructorDisplayAtom(cx, &name))
+        return false;
+
+    if (name) {
+        args.rval().setString(name);
+    } else {
+        args.rval().setNull();
+    }
+    return true;
+}
+
 static const JSFunctionSpecWithHelp TestingFunctions[] = {
     JS_FN_HELP("gc", ::GC, 0, 0,
 "gc([obj] | 'compartment' [, 'shrinking'])",
@@ -2960,6 +2986,11 @@ gc::ZealModeHelpText),
 "  Explicitly enable source discarding in the current compartment.  The default is that "
 "  source discarding is not explicitly enabled."),
 
+    JS_FN_HELP("getConstructorName", GetConstructorName, 1, 0,
+"getConstructorName(object)",
+"  If the given object was created with `new Ctor`, return the constructor's display name. "
+"  Otherwise, return null."),
+
     JS_FS_HELP_END
 };
 

js/src/jit-test/tests/basic/constructor-name.js

@@ -0,0 +1,28 @@
+function Ctor() {}
+
+var nested = {};
+nested.Ctor = function () {};
+nested.object = {};
+
+function makeInstance() {
+  let LexicalCtor = function () {};
+  return new LexicalCtor;
+}
+
+function makeObject() {
+  let object = {};
+  return object;
+}
+
+let tests = [
+  { name: "Ctor",                     object: new Ctor        },
+  { name: "nested.Ctor",              object: new nested.Ctor },
+  { name: "makeInstance/LexicalCtor", object: makeInstance()  },
+  { name: null,                       object: {}              },
+  { name: null,                       object: nested.object   },
+  { name: null,                       object: makeObject()    },
+];
+
+for (let { name, object } of tests) {
+  assertEq(getConstructorName(object), name);
+}

js/src/jsobj.cpp

@@ -4106,3 +4106,32 @@ JSObject::traceChildren(JSTracer* trc)
         } while (false);
     }
 }
+
+static JSAtom*
+displayAtomFromObjectGroup(ObjectGroup& group)
+{
+    TypeNewScript* script = group.newScript();
+    if (!script)
+        return nullptr;
+
+    return script->function()->displayAtom();
+}
+
+bool
+JSObject::constructorDisplayAtom(JSContext* cx, js::MutableHandleAtom name)
+{
+    ObjectGroup *g = getGroup(cx);
+    if (!g)
+        return false;
+
+    name.set(displayAtomFromObjectGroup(*g));
+    return true;
+}
+
+JSAtom*
+JSObject::maybeConstructorDisplayAtom() const
+{
+    if (hasLazyGroup())
+        return nullptr;
+    return displayAtomFromObjectGroup(*group());
+}

js/src/jsobj.h

@@ -254,6 +254,20 @@ class JSObject : public js::gc::Cell
      */
     inline bool isIndexed() const;
 
+    /*
+     * If this object was instantiated with `new Ctor`, return the constructor's
+     * display atom. Otherwise, return nullptr.
+     */
+    bool constructorDisplayAtom(JSContext* cx, js::MutableHandleAtom name);
+
+    /*
+     * The same as constructorDisplayAtom above, however if this object has a
+     * lazy group, nullptr is returned. This allows for use in situations that
+     * cannot GC and where having some information, even if it is inconsistently
+     * available, is better than no information.
+     */
+    JSAtom* maybeConstructorDisplayAtom() const;
+
     /* GC support. */
 
     void traceChildren(JSTracer* trc);