Issue #1038 ... optimize away trailing return / and return undefined

lib/grammar.js

@@ -58,7 +58,12 @@
       }), o('REGEX', function() {
         return new Literal($1);
       }), o('BOOL', function() {
-        return new Literal($1 === 'undefined' ? 'void 0' : $1);
+        var val;
+        val = new Literal($1);
+        if ($1 === 'undefined') {
+          val.isUndefined = true;
+        }
+        return val;
       })
     ],
     Assign: [

lib/nodes.js

@@ -221,6 +221,9 @@
         expr = this.expressions[len];
         if (!(expr instanceof Comment)) {
           this.expressions[len] = expr.makeReturn();
+          if (expr instanceof Return && !expr.expression) {
+            this.expressions.splice(len, 1);
+          }
           break;
         }
       }
@@ -351,7 +354,7 @@
     };
     Literal.prototype.compileNode = function(o) {
       var code;
-      code = this.value.reserved ? "\"" + this.value + "\"" : this.value;
+      code = this.isUndefined ? 'void 0' : this.value.reserved ? "\"" + this.value + "\"" : this.value;
       if (this.isStatement()) {
         return "" + this.tab + code + ";";
       } else {
@@ -365,8 +368,10 @@
   })();
   exports.Return = Return = (function() {
     __extends(Return, Base);
-    function Return(expression) {
-      this.expression = expression;
+    function Return(expr) {
+      if (expr && !expr.unwrap().isUndefined) {
+        this.expression = expr;
+      }
     }
     Return.prototype.children = ['expression'];
     Return.prototype.isStatement = YES;

lib/parser.js

@@ -71,7 +71,14 @@ case 30:this.$ = new yy.Literal($$[$0]);
 break;
 case 31:this.$ = new yy.Literal($$[$0]);
 break;
-case 32:this.$ = new yy.Literal($$[$0] === 'undefined' ? 'void 0' : $$[$0]);
+case 32:this.$ = (function () {
+        var val;
+        val = new yy.Literal($$[$0]);
+        if ($$[$0] === 'undefined') {
+          val.isUndefined = true;
+        }
+        return val;
+      }());
 break;
 case 33:this.$ = new yy.Assign($$[$0-2], $$[$0]);
 break;

src/grammar.coffee

@@ -127,7 +127,9 @@ grammar =
     o 'JS',                                     -> new Literal $1
     o 'REGEX',                                  -> new Literal $1
     o 'BOOL',                                   ->
-      new Literal if $1 is 'undefined' then 'void 0' else $1
+      val = new Literal $1
+      val.isUndefined = yes if $1 is 'undefined'
+      val
   ]
 
   # Assignment of a variable, property, or index to a value.

src/nodes.coffee

@@ -196,6 +196,7 @@ exports.Expressions = class Expressions extends Base
       expr = @expressions[len]
       if expr not instanceof Comment
         @expressions[len] = expr.makeReturn()
+        @expressions.splice(len, 1) if expr instanceof Return and not expr.expression
         break
     this
 
@@ -289,7 +290,12 @@ exports.Literal = class Literal extends Base
     if not (o and (o.loop or o.block and (@value isnt 'continue'))) then this else no
 
   compileNode: (o) ->
-    code = if @value.reserved then "\"#{@value}\"" else @value
+    code = if @isUndefined
+      'void 0'
+    else if @value.reserved
+      "\"#{@value}\""
+    else
+      @value
     if @isStatement() then "#{@tab}#{code};" else code
 
   toString: ->
@@ -300,7 +306,8 @@ exports.Literal = class Literal extends Base
 # A `return` is a *pureStatement* -- wrapping it in a closure wouldn't
 # make sense.
 exports.Return = class Return extends Base
-  constructor: (@expression) ->
+  constructor: (expr) ->
+    @expression = expr if expr and not expr.unwrap().isUndefined
 
   children: ['expression']