simplifying generated output for unless/is to (a isnt b) instead of not (a is b). Ticket #617

lib/lexer.js

@@ -305,7 +305,7 @@
       return true;
     };
     Lexer.prototype.newlineToken = function(newlines) {
-      if (!(this.tag() === 'TERMINATOR')) {
+      if (this.tag() !== 'TERMINATOR') {
         this.token('TERMINATOR', "\n");
       }
       return true;
@@ -523,7 +523,7 @@
         if (pi < i && pi < str.length - 1) {
           tokens.push(['STRING', quote + str.substring(pi, i) + quote]);
         }
-        if (!(tokens[0][0] === 'STRING')) {
+        if (tokens[0][0] !== 'STRING') {
           tokens.unshift(['STRING', '""']);
         }
         interpolated = tokens.length > 1;

lib/nodes.js

@@ -1242,6 +1242,10 @@
       '==': '===',
       '!=': '!=='
     };
+    OpNode.prototype.INVERSIONS = {
+      '!==': '===',
+      '===': '!=='
+    };
     OpNode.prototype.CHAINABLE = ['<', '>', '>=', '<=', '===', '!=='];
     OpNode.prototype.ASSIGNMENT = ['||=', '&&=', '?='];
     OpNode.prototype.PREFIX_OPERATORS = ['typeof', 'delete'];
@@ -1250,13 +1254,19 @@
     OpNode.prototype.isUnary = function() {
       return !this.second;
     };
-    OpNode.prototype.isMutator = function() {
+    OpNode.prototype.isInvertable = function() {
       var _b;
-      return ends(this.operator, '=') && !('===' === (_b = this.operator) || '!==' === _b);
+      return ('===' === (_b = this.operator) || '!==' === _b);
+    };
+    OpNode.prototype.isMutator = function() {
+      return ends(this.operator, '=') && !this.isInvertable();
     };
     OpNode.prototype.isChainable = function() {
       return include(this.CHAINABLE, this.operator);
     };
+    OpNode.prototype.invert = function() {
+      return (this.operator = this.INVERSIONS[this.operator]);
+    };
     OpNode.prototype.toString = function(idt) {
       return OpNode.__superClass__.toString.call(this, idt, this["class"] + ' ' + this.operator);
     };
@@ -1637,7 +1647,11 @@
       this.condition = _b;
       this.tags || (this.tags = {});
       if (this.tags.invert) {
-        this.condition = new OpNode('!', new ParentheticalNode(this.condition));
+        if (this.condition instanceof OpNode && this.condition.isInvertable()) {
+          this.condition.invert();
+        } else {
+          this.condition = new OpNode('!', new ParentheticalNode(this.condition));
+        }
       }
       this.elseBody = null;
       this.isChain = false;

lib/rewriter.js

@@ -63,7 +63,7 @@
     Rewriter.prototype.adjustComments = function() {
       return this.scanTokens(function(token, i) {
         var _c, _d, after, before, post, prev;
-        if (!(token[0] === 'HERECOMMENT')) {
+        if (token[0] !== 'HERECOMMENT') {
           return 1;
         }
         _c = [this.tokens[i - 2], this.tokens[i - 1], this.tokens[i + 1], this.tokens[i + 2]];

src/nodes.coffee

@@ -1059,6 +1059,11 @@ exports.OpNode = class OpNode extends BaseNode
     '==': '==='
     '!=': '!=='
 
+  # The map of invertable operators.
+  INVERSIONS:
+    '!==': '==='
+    '===': '!=='
+
   # The list of operators for which we perform
   # [Python-style comparison chaining](http://docs.python.org/reference/expressions.html#notin).
   CHAINABLE:        ['<', '>', '>=', '<=', '===', '!==']
@@ -1081,12 +1086,18 @@ exports.OpNode = class OpNode extends BaseNode
   isUnary: ->
     not @second
 
+  isInvertable: ->
+    @operator in ['===', '!==']
+
   isMutator: ->
-    ends(@operator, '=') and @operator not in ['===', '!==']
+    ends(@operator, '=') and not @isInvertable()
 
   isChainable: ->
     include(@CHAINABLE, @operator)
 
+  invert: ->
+    @operator = @INVERSIONS[@operator]
+
   toString: (idt) ->
     super(idt, @class + ' ' + @operator)
 
@@ -1369,7 +1380,11 @@ exports.IfNode = class IfNode extends BaseNode
 
   constructor: (@condition, @body, @tags) ->
     @tags      or= {}
-    @condition = new OpNode('!', new ParentheticalNode(@condition)) if @tags.invert
+    if @tags.invert
+      if @condition instanceof OpNode and @condition.isInvertable()
+        @condition.invert()
+      else
+        @condition = new OpNode '!', new ParentheticalNode @condition
     @elseBody = null
     @isChain  = false