Bug 848062 - Make arrow functions inherit the value of 'this' from the enclosing scope. r=bhackett.

js/src/ion/IonBuilder.cpp

@@ -6929,6 +6929,9 @@ bool
 IonBuilder::jsop_lambda(JSFunction *fun)
 {
     JS_ASSERT(script()->analysis()->usesScopeChain());
+    if (fun->isArrow())
+        return abort("bound arrow function");
+
     MLambda *ins = MLambda::New(current->scopeChain(), fun);
     current->add(ins);
     current->push(ins);

js/src/jit-test/tests/arrow-functions/this-1.js

@@ -0,0 +1,17 @@
+// 'this' is lexically scoped in arrow functions
+
+var obj = {
+    f: function (expected) {
+        assertEq(this, expected);
+        return a => this;
+    }
+};
+
+var g = obj.f(obj);
+assertEq(g(), obj);
+
+var obj2 = {f: obj.f};
+var g2 = obj2.f(obj2);
+assertEq(g2(), obj2);
+assertEq(g(), obj);
+

js/src/jit-test/tests/arrow-functions/this-2.js

@@ -0,0 +1,14 @@
+// 'this' is lexically scoped in direct eval code in arrow functions
+
+var obj = {
+    f: function (s) {
+        dis();
+        return a => eval(s);
+    }
+};
+
+var g = obj.f("this");
+assertEq(g(), obj);
+
+var obj2 = {g: g, fail: true};
+assertEq(obj2.g(), obj);

js/src/jit-test/tests/arrow-functions/this-3.js

@@ -0,0 +1,13 @@
+// 'this' is lexically scoped in arrow functions in direct eval code
+
+var obj = {
+    f: function (s) {
+        return eval(s);
+    }
+};
+
+var g = obj.f("a => this");
+assertEq(g(), obj);
+
+var obj2 = {g: g, fail: true};
+assertEq(obj2.g(), obj);

js/src/jit-test/tests/arrow-functions/this-4.js

@@ -0,0 +1,5 @@
+// 'this' in a toplevel arrow is the global object.
+
+var f = () => this;
+assertEq(f(), this);
+assertEq({f: f}.f(), this);

js/src/jsfun.cpp

@@ -623,6 +623,16 @@ js::FunctionToString(JSContext *cx, HandleFunction fun, bool bodyOnly, bool lamb
     StringBuffer out(cx);
     RootedScript script(cx);
 
+    // If the object is an automatically-bound arrow function, get the source
+    // of the pre-binding target.
+    if (fun->isBoundFunction()) {
+        JSObject *target = fun->getBoundFunctionTarget();
+        if (target->isFunction() && target->toFunction()->isArrow()) {
+            RootedFunction targetfun(cx, target->toFunction());
+            return FunctionToString(cx, targetfun, bodyOnly, lambdaParen);
+        }
+    }
+
     if (fun->hasScript()) {
         script = fun->nonLazyScript();
         if (script->isGeneratorExp) {

js/src/jsinferinlines.h

@@ -724,6 +724,9 @@ UseNewTypeForClone(JSFunction *fun)
     if (fun->nonLazyScript()->shouldCloneAtCallsite)
         return true;
 
+    if (fun->isArrow())
+        return true;
+
     if (fun->hasSingletonType())
         return false;
 

js/src/jsinterp.cpp

@@ -2775,10 +2775,9 @@ BEGIN_CASE(JSOP_LAMBDA)
     RootedFunction &fun = rootFunction0;
     fun = script->getFunction(GET_UINT32_INDEX(regs.pc));
 
-    JSFunction *obj = CloneFunctionObjectIfNotSingleton(cx, fun, regs.fp()->scopeChain());
+    JSObject *obj = Lambda(cx, fun, regs.fp()->scopeChain());
     if (!obj)
         goto error;
-
     JS_ASSERT(obj->getProto());
     PUSH_OBJECT(*obj);
 }
@@ -3461,6 +3460,20 @@ js::Lambda(JSContext *cx, HandleFunction fun, HandleObject parent)
     if (!clone)
         return NULL;
 
+    if (fun->isArrow()) {
+        StackFrame *fp = cx->fp();
+
+        // Note that this will assert if called from Ion code. Ion can't yet
+        // emit code for a bound arrow function (bug 851913).
+        if (!ComputeThis(cx, fp))
+            return NULL;
+
+        RootedValue thisval(cx, fp->thisValue());
+        clone = js_fun_bind(cx, clone, thisval, NULL, 0);
+        if (!clone)
+            return NULL;
+    }
+
     JS_ASSERT(clone->global() == clone->global());
     return clone;
 }

js/src/methodjit/StubCalls.cpp

@@ -1016,11 +1016,11 @@ JSObject * JS_FASTCALL
 stubs::Lambda(VMFrame &f, JSFunction *fun_)
 {
     RootedFunction fun(f.cx, fun_);
-    fun = CloneFunctionObjectIfNotSingleton(f.cx, fun, f.fp()->scopeChain());
-    if (!fun)
+    JSObject *clone = Lambda(f.cx, fun, f.fp()->scopeChain());
+    if (!clone)
         THROWV(NULL);
 
-    return fun;
+    return clone;
 }
 
 void JS_FASTCALL