support transparent as a color but do not alter existing output of transparent and rgba()

lib/less/colors.js

@@ -140,7 +140,6 @@
         'teal':'#008080',
         'thistle':'#d8bfd8',
         'tomato':'#ff6347',
-        // 'transparent':'rgba(0,0,0,0)',
         'turquoise':'#40e0d0',
         'violet':'#ee82ee',
         'wheat':'#f5deb3',

lib/less/parser.js

@@ -657,12 +657,11 @@ less.Parser = function Parser(env) {
                     var k;
 
                     if (k = $(/^[_A-Za-z-][_A-Za-z0-9-]*/)) {
-                        if (tree.colors.hasOwnProperty(k)) {
-                            // detect named color
-                            return new(tree.Color)(tree.colors[k].slice(1));
-                        } else {
-                            return new(tree.Keyword)(k);
+                        var color = tree.Color.fromKeyword(k);
+                        if (color) {
+                            return color;
                         }
+                        return new(tree.Keyword)(k);
                     }
                 },
 

lib/less/tree/color.js

@@ -22,6 +22,9 @@ tree.Color = function (rgb, a) {
     }
     this.alpha = typeof(a) === 'number' ? a : 1;
 };
+
+var transparentKeyword = "transparent";
+
 tree.Color.prototype = {
     type: "Color",
     eval: function () { return this; },
@@ -38,6 +41,9 @@ tree.Color.prototype = {
         // which has better compatibility with older browsers.
         // Values are capped between `0` and `255`, rounded and zero-padded.
         if (this.alpha < 1.0) {
+            if (this.alpha === 0 && this.isTransparentKeyword) {
+                return transparentKeyword;
+            }
             return "rgba(" + this.rgb.map(function (c) {
                 return Math.round(c);
             }).concat(this.alpha).join(',' + (compress ? '' : ' ')) + ")";
@@ -156,5 +162,17 @@ tree.Color.prototype = {
     }
 };
 
+tree.Color.fromKeyword = function(keyword) {
+    if (tree.colors.hasOwnProperty(keyword)) {
+        // detect named color
+        return new(tree.Color)(tree.colors[keyword].slice(1));
+    }
+    if (keyword === transparentKeyword) {
+        var transparent = new(tree.Color)([0, 0, 0], 0);
+        transparent.isTransparentKeyword = true;
+        return transparent;
+    }
+};
+
 
 })(require('../tree'));

test/css/functions.css

@@ -102,11 +102,13 @@
   mix-0: #ffff00;
   mix-100: #ff0000;
   mix-weightless: #ff8000;
+  mixt: rgba(255, 0, 0, 0.5);
 }
 #built-in .is-a {
   color: true;
   color1: true;
   color2: true;
+  color3: true;
   keyword: true;
   number: true;
   string: true;
@@ -117,6 +119,8 @@
 }
 #alpha {
   alpha: rgba(153, 94, 51, 0.6);
+  alpha2: 0.5;
+  alpha3: 0;
 }
 #blendmodes {
   multiply: #ed0000;

test/less/functions.less

@@ -111,11 +111,13 @@
   mix-0: mix(#ff0000, #ffff00, 0);
   mix-100: mix(#ff0000, #ffff00, 100);
   mix-weightless: mix(#ff0000, #ffff00);
+  mixt: mix(#ff0000, transparent);
 
   .is-a {
     color: iscolor(#ddd);
     color1: iscolor(red);
     color2: iscolor(rgb(0, 0, 0));
+    color3: iscolor(transparent);
     keyword: iskeyword(hello);
     number: isnumber(32);
     string: isstring("hello");
@@ -128,6 +130,8 @@
 
 #alpha {
   alpha: darken(hsla(25, 50%, 50%, 0.6), 10%);
+  alpha2: alpha(rgba(3, 4, 5, 0.5));
+  alpha3: alpha(transparent);
 }
 
 #blendmodes {