Bug 574132 - Implement harmony rest parameters. r=jorendorff

js/src/frontend/BytecodeCompiler.cpp

@@ -227,6 +227,9 @@ frontend::CompileScript(JSContext *cx, JSObject *scopeChain, StackFrame *callerF
     }
 #endif
 
+    if (!parser.checkForArgumentsAndRest())
+        goto out;
+
     /*
      * Nowadays the threaded interpreter needs a stop instruction, so we
      * do have to emit that here.

js/src/frontend/BytecodeEmitter.cpp

@@ -5890,6 +5890,18 @@ frontend::EmitTree(JSContext *cx, BytecodeEmitter *bce, ParseNode *pn)
                 if (!bce->noteClosedArg(pn2))
                     return JS_FALSE;
             }
+            if (pn2->pn_next == pnlast && bce->sc->fun()->hasRest()) {
+                /* Fill rest parameter. */
+                JS_ASSERT(!bce->sc->funArgumentsHasLocalBinding());
+                bce->switchToProlog();
+                if (Emit1(cx, bce, JSOP_REST) < 0)
+                    return false;
+                if (!EmitVarOp(cx, pn2, JSOP_SETARG, bce))
+                    return false;
+                if (Emit1(cx, bce, JSOP_POP) < 0)
+                    return false;
+                bce->switchToMain();
+            }
         }
         ok = EmitTree(cx, bce, pnlast);
         break;

js/src/frontend/Parser.cpp

@@ -669,22 +669,36 @@ Parser::functionBody(FunctionBodyType type)
         }
     }
 
-    /*
-     * Even if 'arguments' isn't explicitly mentioned, dynamic name lookup
-     * forces an 'arguments' binding.
-     */
-    if (tc->sc->bindingsAccessedDynamically() && !tc->sc->bindings.hasBinding(context, arguments)) {
+    bool hasRest = tc->sc->fun()->hasRest();
+    BindingKind bindKind = tc->sc->bindings.lookup(context, arguments, NULL);
+    switch (bindKind) {
+      case NONE:
+        /* Functions with rest parameters are free from arguments. */
+        if (hasRest)
+            break;
+
+        /*
+         * Even if 'arguments' isn't explicitly mentioned, dynamic name lookup
+         * forces an 'arguments' binding.
+         */
+        if (!tc->sc->bindingsAccessedDynamically())
+            break;
         if (!tc->sc->bindings.addVariable(context, arguments))
             return NULL;
-    }
 
-    /*
-     * Now that all possible 'arguments' bindings have been added, note whether
-     * 'arguments' has a local binding and whether it unconditionally needs an
-     * arguments object.
-     */
-    BindingKind bindKind = tc->sc->bindings.lookup(context, arguments, NULL);
-    if (bindKind == VARIABLE || bindKind == CONSTANT) {
+        /* 'arguments' is now bound, so fall through. */
+      case VARIABLE:
+      case CONSTANT:        
+        if (hasRest) {
+            reportErrorNumber(NULL, JSREPORT_ERROR, JSMSG_ARGUMENTS_AND_REST);
+            return NULL;
+        }
+
+        /*
+         * Now that all possible 'arguments' bindings have been added, note whether
+         * 'arguments' has a local binding and whether it unconditionally needs an
+         * arguments object.
+         */
         tc->sc->setFunArgumentsHasLocalBinding();
 
         /* Dynamic scope access destroys all hope of optimization. */
@@ -705,13 +719,34 @@ Parser::functionBody(FunctionBodyType type)
                     tc->sc->setFunDefinitelyNeedsArgsObj();
                     break;
                 }
-             }
+            }
         }
+        break;
+      case ARGUMENT:
+        break;
     }
 
     return pn;
 }
 
+bool
+Parser::checkForArgumentsAndRest()
+{
+    JS_ASSERT(!tc->sc->inFunction);
+    if (callerFrame && callerFrame->isFunctionFrame() && callerFrame->fun()->hasRest()) {
+        PropertyName *arguments = context->runtime->atomState.argumentsAtom;
+        for (AtomDefnRange r = tc->lexdeps->all(); !r.empty(); r.popFront()) {
+            if (r.front().key() == arguments) {
+                reportErrorNumber(NULL, JSREPORT_ERROR, JSMSG_ARGUMENTS_AND_REST);
+                return false;
+            }
+        }
+        /* We're not in a function context, so we don't expect any bindings. */
+        JS_ASSERT(tc->sc->bindings.lookup(context, arguments, NULL) == NONE);
+    }
+    return true;
+}
+
 // Create a placeholder Definition node for |atom|.
 // Nb: unlike most functions that are passed a Parser, this one gets a
 // SharedContext passed in separately, because in this case |sc| may not equal
@@ -1250,13 +1285,15 @@ LeaveFunction(ParseNode *fn, Parser *parser, PropertyName *funName = NULL,
 }
 
 bool
-Parser::functionArguments(ParseNode **listp)
+Parser::functionArguments(ParseNode **listp, bool &hasRest)
 {
     if (tokenStream.getToken() != TOK_LP) {
         reportErrorNumber(NULL, JSREPORT_ERROR, JSMSG_PAREN_BEFORE_FORMAL);
         return false;
     }
 
+    hasRest = false;
+
     if (!tokenStream.matchToken(TOK_RP)) {
 #if JS_HAS_DESTRUCTURING
         JSAtom *duplicatedArg = NULL;
@@ -1265,6 +1302,10 @@ Parser::functionArguments(ParseNode **listp)
 #endif
 
         do {
+            if (hasRest) {
+                reportErrorNumber(NULL, JSREPORT_ERROR, JSMSG_PARAMETER_AFTER_REST);
+                return false;
+            }
             switch (TokenKind tt = tokenStream.getToken()) {
 #if JS_HAS_DESTRUCTURING
               case TOK_LB:
@@ -1326,6 +1367,18 @@ Parser::functionArguments(ParseNode **listp)
               }
 #endif /* JS_HAS_DESTRUCTURING */
 
+              case TOK_TRIPLEDOT:
+              {
+                hasRest = true;
+                tt = tokenStream.getToken();
+                if (tt != TOK_NAME) {
+                    if (tt != TOK_ERROR)
+                        reportErrorNumber(NULL, JSREPORT_ERROR, JSMSG_NO_REST_NAME);
+                    return false;
+                }
+                /* Fall through */
+              }
+
               case TOK_NAME:
               {
                 RootedVar<PropertyName*> name(context, tokenStream.currentToken().name());
@@ -1519,10 +1572,13 @@ Parser::functionDef(HandlePropertyName funName, FunctionType type, FunctionSynta
 
     /* Now parse formal argument list and compute fun->nargs. */
     ParseNode *prelude = NULL;
-    if (!functionArguments(&prelude))
+    bool hasRest;
+    if (!functionArguments(&prelude, hasRest))
         return NULL;
 
     fun->setArgCount(funsc.bindings.numArgs());
+    if (hasRest)
+        fun->setHasRest();
 
 #if JS_HAS_DESTRUCTURING
     /*

js/src/frontend/Parser.h

@@ -146,6 +146,8 @@ struct Parser : private AutoGCRooter
     enum FunctionBodyType { StatementListBody, ExpressionBody };
     ParseNode *functionBody(FunctionBodyType type);
 
+    bool checkForArgumentsAndRest();
+
   private:
     /*
      * JS parsers, from lowest to highest precedence.
@@ -208,7 +210,7 @@ struct Parser : private AutoGCRooter
      * Additional JS parsers.
      */
     enum FunctionType { Getter, Setter, Normal };
-    bool functionArguments(ParseNode **list);
+    bool functionArguments(ParseNode **list, bool &hasRest);
 
     ParseNode *functionDef(HandlePropertyName name, FunctionType type, FunctionSyntaxKind kind);
 

js/src/frontend/TokenStream.cpp

@@ -1520,12 +1520,18 @@ TokenStream::getTokenInternal()
             numStart = userbuf.addressOfNextRawChar() - 2;
             goto decimal_dot;
         }
-#if JS_HAS_XML_SUPPORT
         if (c == '.') {
+            qc = getCharIgnoreEOL();
+            if (qc == '.') {
+                tt = TOK_TRIPLEDOT;
+                goto out;
+            }
+            ungetCharIgnoreEOL(qc);
+#if JS_HAS_XML_SUPPORT
             tt = TOK_DBLDOT;
             goto out;
-        }
 #endif
+        }
         ungetCharIgnoreEOL(c);
         tt = TOK_DOT;
         goto out;
@@ -2158,6 +2164,7 @@ TokenKindToString(TokenKind tt)
       case TOK_INC:             return "TOK_INC";
       case TOK_DEC:             return "TOK_DEC";
       case TOK_DOT:             return "TOK_DOT";
+      case TOK_TRIPLEDOT:       return "TOK_TRIPLEDOT";
       case TOK_LB:              return "TOK_LB";
       case TOK_RB:              return "TOK_RB";
       case TOK_LC:              return "TOK_LC";

js/src/frontend/TokenStream.h

@@ -47,6 +47,7 @@ enum TokenKind {
     TOK_MOD,                       /* modulus */
     TOK_INC, TOK_DEC,              /* increment/decrement (++ --) */
     TOK_DOT,                       /* member operator (.) */
+    TOK_TRIPLEDOT,                 /* for rest arguments (...) */
     TOK_LB, TOK_RB,                /* left and right brackets */
     TOK_LC, TOK_RC,                /* left and right curlies (braces) */
     TOK_LP, TOK_RP,                /* left and right parentheses */

js/src/jit-test/tests/arguments/rest-arguments-as-parameters.js

@@ -0,0 +1,9 @@
+function f1(...arguments) {
+    assertEq("1,2,3", arguments.toString());
+}
+f1(1, 2, 3);
+function f2(arguments, ...rest) {
+    assertEq(arguments, 42);
+    assertEq("1,2,3", rest.toString());
+}
+f2(42, 1, 2, 3);

js/src/jit-test/tests/arguments/rest-basic.js

@@ -0,0 +1,15 @@
+function check(expected, ...rest) {
+    assertEq(expected.toString(), rest.toString());
+}
+
+assertEq(check.length, 1);
+check([]);
+check(['a', 'b'], 'a', 'b');
+check(['a', 'b', 'c', 'd'], 'a', 'b', 'c', 'd');
+check.apply(null, [['a', 'b'], 'a', 'b'])
+check.call(null, ['a', 'b'], 'a', 'b')
+
+var g = newGlobal('new-compartment');
+g.eval("function f(...rest) { return rest; }");
+var a = g.f(1, 2, 3);
+assertEq(a instanceof g.Array, true);

js/src/jit-test/tests/arguments/rest-debugger.js

@@ -0,0 +1,17 @@
+var g = newGlobal('new-compartment');
+g.eval("function f(...x) {}");
+var dbg = new Debugger;
+var gw = dbg.addDebuggee(g);
+var fw = gw.getOwnPropertyDescriptor("f").value;
+assertEq(fw.parameterNames.toString(), "x");
+
+var g = newGlobal('new-compartment');
+g.eval("function f(...rest) { debugger; }");
+var dbg = Debugger(g);
+dbg.onDebuggerStatement = function (frame) {
+    var result = frame.eval("arguments");
+    assertEq("throw" in result, true);
+    var result2 = frame.evalWithBindings("exc instanceof SyntaxError", {exc: result.throw});
+    assertEq(result2.return, true);
+};
+g.f();

js/src/jit-test/tests/arguments/rest-decompile.js

@@ -0,0 +1,2 @@
+g = (function (...rest) { return rest; });
+assertEq(g.toString(), "function (...rest) {\n    return rest;\n}");

js/src/jit-test/tests/arguments/rest-disallow-arguments-strict.js

@@ -0,0 +1,8 @@
+"use strict";
+load(libdir + "asserts.js");
+assertThrowsInstanceOf(function () {
+    eval("(function (...arguments) {})");
+}, SyntaxError);
+assertThrowsInstanceOf(function () {
+    eval("(function (...eval) {})");
+}, SyntaxError);

js/src/jit-test/tests/arguments/rest-disallow-arguments.js

@@ -0,0 +1,30 @@
+load(libdir + "asserts.js");
+var ieval = eval;
+
+// Now for a tour of the various ways you can access arguments.
+assertThrowsInstanceOf(function () {
+    ieval("function x(...rest) { arguments; }");
+}, SyntaxError)
+assertThrowsInstanceOf(function () {
+    Function("...rest", "arguments;");
+}, SyntaxError);
+assertThrowsInstanceOf(function (...rest) {
+    eval("arguments;");
+}, SyntaxError);
+assertThrowsInstanceOf(function (...rest) {
+    eval("arguments = 42;");
+}, SyntaxError);
+
+function g(...rest) {
+    assertThrowsInstanceOf(h, Error);
+}
+function h() {
+    g.arguments;
+}
+g();
+
+// eval() is evil, but you can still use it with rest parameters!
+function still_use_eval(...rest) {
+    eval("x = 4");
+}
+still_use_eval();

js/src/jit-test/tests/arguments/rest-in-Function.js

@@ -0,0 +1,3 @@
+h = Function("a", "b", "c", "...rest", "return rest.toString();");
+assertEq(h.length, 3);
+assertEq(h(1, 2, 3, 4, 5), "4,5");

js/src/jit-test/tests/arguments/rest-invalid-syntax.js

@@ -0,0 +1,12 @@
+load(libdir + "asserts.js");
+var ieval = eval;
+var offenders = [["..."], ["...rest"," x"], ["...rest", "[x]"],
+                 ["...rest", "...rest2"]];
+for (var arglist of offenders) {
+    assertThrowsInstanceOf(function () {
+        ieval("function x(" + arglist.join(", ") + ") {}");
+    }, SyntaxError);
+    assertThrowsInstanceOf(function () {
+        Function.apply(null, arglist.concat("return 0;"));
+    }, SyntaxError);
+}

js/src/jit-test/tests/arguments/rest-nested-arguments.js

@@ -0,0 +1,7 @@
+function f(...rest) {
+    function nested() {
+        return arguments.length;
+    }
+    return nested;
+}
+assertEq(f()(1, 2, 3), 3);

js/src/jit-test/tests/arguments/rest-nested.js

@@ -0,0 +1,7 @@
+function f(...rest) {
+    function nested () {
+        return rest;
+    }
+    return nested;
+}
+assertEq(f(1, 2, 3)().toString(), [1, 2, 3].toString());

js/src/jit-test/tests/arguments/rest-underflow.js

@@ -0,0 +1,9 @@
+function f(a, b, c, ...rest) {
+    assertEq(a, 1);
+    assertEq(b, undefined);
+    assertEq(c, undefined);
+    assertEq(Array.isArray(rest), true);
+    assertEq(rest.length, 0);
+    assertEq(Object.getPrototypeOf(rest), Array.prototype);
+}
+f(1);

js/src/js.msg

@@ -345,3 +345,7 @@ MSG_DEF(JSMSG_NOT_ITERABLE,           291, 1, JSEXN_TYPEERR, "{0} is not iterabl
 MSG_DEF(JSMSG_QUERY_LINE_WITHOUT_URL, 292, 0, JSEXN_TYPEERR, "findScripts query object has 'line' property, but no 'url' property")
 MSG_DEF(JSMSG_QUERY_INNERMOST_WITHOUT_LINE_URL, 293, 0, JSEXN_TYPEERR, "findScripts query object has 'innermost' property without both 'url' and 'line' properties")
 MSG_DEF(JSMSG_DEBUG_VARIABLE_NOT_FOUND, 294, 0, JSEXN_TYPEERR, "variable not found in environment")
+MSG_DEF(JSMSG_PARAMETER_AFTER_REST,   295, 0, JSEXN_SYNTAXERR, "parameter after rest parameter")
+MSG_DEF(JSMSG_NO_REST_NAME,           296, 0, JSEXN_SYNTAXERR, "no parameter name after ...")
+MSG_DEF(JSMSG_ARGUMENTS_AND_REST,     297, 0, JSEXN_SYNTAXERR, "'arguments' object may not be used in conjunction with a rest parameter")
+MSG_DEF(JSMSG_FUNCTION_ARGUMENTS_AND_REST, 298, 0, JSEXN_ERR, "the 'arguments' property of a function with a rest parameter may not be used")

js/src/jsapi.h

@@ -2184,7 +2184,7 @@ class AutoIdRooter : private AutoGCRooter
 
 #define JSFUN_HEAVYWEIGHT_TEST(f)  ((f) & JSFUN_HEAVYWEIGHT)
 
-/* 0x0100 is unused */
+#define JSFUN_HAS_REST          0x0100  /* function has a rest (...) parameter */
 #define JSFUN_CONSTRUCTOR     0x0200    /* native that can be called as a ctor
                                            without creating a this object */
 

js/src/jsfun.cpp

@@ -102,6 +102,10 @@ fun_getProperty(JSContext *cx, HandleObject obj_, HandleId id, Value *vp)
     StackFrame *fp = iter.fp();
 
     if (JSID_IS_ATOM(id, cx->runtime->atomState.argumentsAtom)) {
+        if (fun->hasRest()) {
+            JS_ReportErrorNumber(cx, js_GetErrorMessage, NULL, JSMSG_FUNCTION_ARGUMENTS_AND_REST);
+            return false;
+        }
         /* Warn if strict about f.arguments or equivalent unqualified uses. */
         if (!JS_ReportErrorFlagsAndNumber(cx, JSREPORT_WARNING | JSREPORT_STRICT, js_GetErrorMessage,
                                           NULL, JSMSG_DEPRECATED_USAGE, js_arguments_str)) {
@@ -291,7 +295,7 @@ fun_resolve(JSContext *cx, HandleObject obj, HandleId id, unsigned flags,
 
         Value v;
         if (JSID_IS_ATOM(id, cx->runtime->atomState.lengthAtom))
-            v.setInt32(fun->nargs);
+            v.setInt32(fun->nargs - fun->hasRest());
         else
             v.setString(fun->atom ? fun->atom : cx->runtime->emptyString);
 
@@ -1003,6 +1007,8 @@ Function(JSContext *cx, unsigned argc, Value *vp)
     Bindings bindings(cx);
     Bindings::StackRoot bindingsRoot(cx, &bindings);
 
+    bool hasRest = false;
+
     const char *filename;
     unsigned lineno;
     JSPrincipals *originPrincipals;
@@ -1092,8 +1098,28 @@ Function(JSContext *cx, unsigned argc, Value *vp)
                  * Check that it's a name.  This also implicitly guards against
                  * TOK_ERROR, which was already reported.
                  */
-                if (tt != TOK_NAME)
-                    return OnBadFormal(cx, tt);
+                if (hasRest) {
+                    ReportCompileErrorNumber(cx, &ts, NULL, JSREPORT_ERROR,
+                                             JSMSG_PARAMETER_AFTER_REST);
+                    return false;
+                }
+
+                if (tt != TOK_NAME) {
+                    if (tt == TOK_TRIPLEDOT) {
+                        hasRest = true;
+                        tt = ts.getToken();
+                        if (tt != TOK_NAME) {
+                            if (tt != TOK_ERROR)
+                                ReportCompileErrorNumber(cx, &ts, NULL,
+                                                         JSREPORT_ERROR,
+                                                         JSMSG_NO_REST_NAME);
+                            return false;
+                        }
+                    }
+                    else {
+                        return OnBadFormal(cx, tt);
+                    }
+                }
 
                 /* Check for a duplicate parameter name. */
                 RootedVar<PropertyName*> name(cx, ts.currentToken().name());
@@ -1156,6 +1182,9 @@ Function(JSContext *cx, unsigned argc, Value *vp)
     if (!fun)
         return false;
 
+    if (hasRest)
+        fun->setHasRest();
+
     bool ok = frontend::CompileFunctionBody(cx, fun, principals, originPrincipals,
                                             &bindings, chars, length, filename, lineno,
                                             cx->findVersion());

js/src/jsfun.h

@@ -63,6 +63,7 @@ struct JSFunction : public JSObject
     } u;
     js::HeapPtrAtom  atom;        /* name for diagnostics and decompiling */
 
+    bool hasRest()           const { return flags & JSFUN_HAS_REST; }
     bool isInterpreted()     const { return kind() >= JSFUN_INTERPRETED; }
     bool isNative()          const { return !isInterpreted(); }
     bool isNativeConstructor() const { return flags & JSFUN_CONSTRUCTOR; }
@@ -85,6 +86,11 @@ struct JSFunction : public JSObject
         this->nargs = nargs;
     }
 
+    void setHasRest() {
+        JS_ASSERT(!hasRest());
+        this->flags |= JSFUN_HAS_REST;
+    }
+
     /* uint16_t representation bounds number of call object dynamic slots. */
     enum { MAX_ARGS_AND_VARS = 2 * ((1U << 16) - 1) };
 

js/src/jsinfer.cpp

@@ -3642,6 +3642,15 @@ ScriptAnalysis::analyzeTypesBytecode(JSContext *cx, unsigned offset,
             pushed[0].addType(cx, Type::MagicArgType());
         break;
 
+      case JSOP_REST: {
+        TypeObject *rest = TypeScript::InitObject(cx, script, pc, JSProto_Array);
+        if (!rest)
+            return false;
+        pushed[0].addType(cx, Type::ObjectType(rest));
+        break;
+      }
+
+
       case JSOP_SETPROP: {
         jsid id = GetAtomId(cx, script, pc, 0);
         poppedTypes(pc, 1)->addSetProperty(cx, script, pc, poppedTypes(pc, 0), id);

js/src/jsinterp.cpp

@@ -1516,7 +1516,6 @@ ADD_EMPTY_CASE(JSOP_UNUSED12)
 ADD_EMPTY_CASE(JSOP_UNUSED13)
 ADD_EMPTY_CASE(JSOP_UNUSED14)
 ADD_EMPTY_CASE(JSOP_UNUSED15)
-ADD_EMPTY_CASE(JSOP_UNUSED16)
 ADD_EMPTY_CASE(JSOP_UNUSED17)
 ADD_EMPTY_CASE(JSOP_UNUSED18)
 ADD_EMPTY_CASE(JSOP_UNUSED19)
@@ -2814,6 +2813,7 @@ END_VARLEN_CASE
 }
 
 BEGIN_CASE(JSOP_ARGUMENTS)
+    JS_ASSERT(!regs.fp()->fun()->hasRest());
     if (script->needsArgsObj()) {
         ArgumentsObject *obj = ArgumentsObject::create(cx, regs.fp());
         if (!obj)
@@ -2824,6 +2824,15 @@ BEGIN_CASE(JSOP_ARGUMENTS)
     }
 END_CASE(JSOP_ARGUMENTS)
 
+BEGIN_CASE(JSOP_REST)
+{
+    JSObject *rest = regs.fp()->createRestParameter(cx);
+    if (!rest)
+        goto error;
+    PUSH_COPY(ObjectValue(*rest));
+}
+END_CASE(JSOP_REST)
+
 BEGIN_CASE(JSOP_CALLALIASEDVAR)
 BEGIN_CASE(JSOP_GETALIASEDVAR)
 {

js/src/jsopcode.cpp

@@ -5537,6 +5537,8 @@ js_DecompileFunction(JSPrinter *jp)
             if (i > 0)
                 js_puts(jp, ", ");
 
+            if (i == fun->nargs - 1 && fun->hasRest())
+                js_puts(jp, "...");
             JSAtom *param = GetArgOrVarAtom(jp, i);
 
 #if JS_HAS_DESTRUCTURING

js/src/jsopcode.tbl

@@ -506,7 +506,8 @@ OPDEF(JSOP_UNUSED24,      220,"unused24",      NULL,  1,  0,  0,  0,  JOF_BYTE)
 OPDEF(JSOP_UNUSED25,      221,"unused25",      NULL,  1,  0,  0,  0,  JOF_BYTE)
 OPDEF(JSOP_UNUSED29,      222,"unused29",      NULL,  1,  0,  0,  0,  JOF_BYTE)
 OPDEF(JSOP_UNUSED30,      223,"unused30",      NULL,  1,  0,  0,  0,  JOF_BYTE)
-OPDEF(JSOP_UNUSED16,      224,"unused16",      NULL,  1,  0,  0,  0,  JOF_BYTE)
+
+OPDEF(JSOP_REST,          224, "rest",         NULL,  1,  0,  1,  0,  JOF_BYTE)
 
 /* Pop the stack, convert to a jsid (int or string), and push back. */
 OPDEF(JSOP_TOID,          225, "toid",         NULL,  1,  1,  1,  0,  JOF_BYTE)

js/src/vm/ArgumentsObject.cpp

@@ -56,6 +56,7 @@ ArgumentsObject *
 ArgumentsObject::create(JSContext *cx, uint32_t argc, HandleObject callee)
 {
     JS_ASSERT(argc <= StackSpace::ARGS_LENGTH_MAX);
+    JS_ASSERT(!callee->toFunction()->hasRest());
 
     RootedVarObject proto(cx, callee->global().getOrCreateObjectPrototype(cx));
     if (!proto)

js/src/vm/Stack-inl.h

@@ -171,6 +171,15 @@ StackFrame::initFixupFrame(StackFrame *prev, StackFrame::Flags flags, void *ncod
     u.nactual = nactual;
 }
 
+inline JSObject *
+StackFrame::createRestParameter(JSContext *cx)
+{
+    JS_ASSERT(fun()->hasRest());
+    unsigned nformal = fun()->nargs - 1, nactual = numActualArgs();
+    unsigned nrest = (nactual > nformal) ? nactual - nformal : 0;
+    return NewDenseCopiedArray(cx, nrest, actualArgs() + nformal);
+}
+
 inline Value &
 StackFrame::canonicalActualArg(unsigned i) const
 {

js/src/vm/Stack.h

@@ -502,6 +502,8 @@ class StackFrame
 
     inline void initInlineFrame(JSFunction *fun, StackFrame *prevfp, jsbytecode *prevpc);
 
+    inline JSObject *createRestParameter(JSContext *cx);
+
     /*
      * Frame slots
      *