Support for for (const ...).

Fixes #213.

Also changes API to pass token type to `parseVar` to reduce string comparison ops.

acorn.js

@@ -1773,7 +1773,7 @@
     case tt._throw: return this.parseThrowStatement(node);
     case tt._try: return this.parseTryStatement(node);
     case tt._let: case tt._const: if (!declaration) this.unexpected(); // NOTE: falls through to _var
-    case tt._var: return this.parseVarStatement(node, starttype.keyword);
+    case tt._var: return this.parseVarStatement(node, starttype);
     case tt._while: return this.parseWhileStatement(node);
     case tt._with: return this.parseWithStatement(node);
     case tt.braceL: return this.parseBlock(); // no point creating a function for this
@@ -1853,13 +1853,13 @@
     this.labels.push(loopLabel);
     this.expect(tt.parenL);
     if (this.type === tt.semi) return this.parseFor(node, null);
-    if (this.type === tt._var || this.type === tt._let) {
-      var init = this.startNode(), varKind = this.type.keyword, isLet = this.type === tt._let;
+    if (this.type === tt._var || this.type === tt._let || this.type === tt._const) {
+      var init = this.startNode(), varKind = this.type;
       this.next();
       this.parseVar(init, true, varKind);
       this.finishNode(init, "VariableDeclaration");
       if ((this.type === tt._in || (this.options.ecmaVersion >= 6 && this.isContextual("of"))) && init.declarations.length === 1 &&
-          !(isLet && init.declarations[0].init))
+          !(varKind !== tt._var && init.declarations[0].init))
         return this.parseForIn(node, init);
       return this.parseFor(node, init);
     }
@@ -2079,12 +2079,18 @@
 
   pp.parseVar = function(node, noIn, kind) {
     node.declarations = [];
-    node.kind = kind;
+    node.kind = kind.keyword;
     for (;;) {
       var decl = this.startNode();
       decl.id = this.parseBindingAtom();
       this.checkLVal(decl.id, true);
-      decl.init = this.eat(tt.eq) ? this.parseMaybeAssign(noIn) : (kind === tt._const.keyword ? this.unexpected() : null);
+      if (this.eat(tt.eq)) {
+        decl.init = this.parseMaybeAssign(noIn);
+      } else if (kind === tt._const && !(this.type === tt._in || (this.options.ecmaVersion >= 6 && this.isContextual("of")))) {
+        this.unexpected();
+      } else {
+        decl.init = null;
+      }
       node.declarations.push(this.finishNode(decl, "VariableDeclarator"));
       if (!this.eat(tt.comma)) break;
     }

acorn_loose.js

@@ -346,7 +346,7 @@
       this.pushCx();
       this.expect(tt.parenL);
       if (this.tok.type === tt.semi) return this.parseFor(node, null);
-      if (this.tok.type === tt._var || this.tok.type === tt._let) {
+      if (this.tok.type === tt._var || this.tok.type === tt._let || this.tok.type === tt._const) {
         var init = this.parseVar(true);
         if (init.declarations.length === 1 && (this.tok.type === tt._in || this.isContextual("of"))) {
           return this.parseForIn(node, init);

test/tests-harmony.js

@@ -14970,6 +14970,55 @@ test("class A { static() {} }", {
   locations: true
 });
 
+// https://github.com/marijnh/acorn/issues/213
+
+test("for (const x of list) process(x);", {
+  type: "Program",
+  body: [{
+    type: "ForOfStatement",
+    left: {
+      type: "VariableDeclaration",
+      declarations: [{
+        type: "VariableDeclarator",
+        id: {
+          type: "Identifier",
+          name: "x",
+          range: [11, 12]
+        },
+        init: null,
+        range: [11, 12]
+      }],
+      kind: "const",
+      range: [5, 12]
+    },
+    right: {
+      type: "Identifier",
+      name: "list",
+      range: [16, 20]
+    },
+    body: {
+      type: "ExpressionStatement",
+      expression: {
+        type: "CallExpression",
+        callee: {
+          type: "Identifier",
+          name: "process",
+          range: [22, 29]
+        },
+        arguments: [{
+          type: "Identifier",
+          name: "x",
+          range: [30, 31]
+        }],
+        range: [22, 32]
+      },
+      range: [22, 33]
+    },
+    range: [0, 33]
+  }],
+  range: [0, 33]
+}, {ecmaVersion: 6, ranges: true});
+
 test("class A { *static() {} }", {
   type: "Program",
   range: [0, 24],

test/tests.js

@@ -28682,7 +28682,39 @@ test("const x = 14, y = 3, z = 1977", {
 
 testFail("const a;", "Unexpected token (1:7)", {ecmaVersion: 6});
 
-testFail("for(const x = 0;;);", "Unexpected token (1:4)", {ecmaVersion: 6});
+test("for(const x = 0;;);", {
+  type: "Program",
+  body: [{
+    type: "ForStatement",
+    init: {
+      type: "VariableDeclaration",
+      declarations: [{
+        type: "VariableDeclarator",
+        id: {
+          type: "Identifier",
+          name: "x",
+          range: [10, 11]
+        },
+        init: {
+          type: "Literal",
+          value: 0,
+          range: [14, 15]
+        },
+        range: [10, 15]
+      }],
+      kind: "const",
+      range: [4, 15]
+    },
+    test: null,
+    update: null,
+    body: {
+      type: "EmptyStatement",
+      range: [18, 19]
+    },
+    range: [0, 19]
+  }],
+  range: [0, 19]
+}, {ecmaVersion: 6, ranges: true});
 
 testFail("for(x of a);", "Unexpected token (1:6)");