accept a function for sourceMapURL (#307)

Author: montmanu

Gruntfile.js

@@ -155,6 +155,17 @@ module.exports = function(grunt) {
         src: 'test/fixtures/style3.less',
         dest: 'tmp/sourceMapWithCustomURL.css'
       },
+      sourceMapURLFunction: {
+        options: {
+          sourceMap: true,
+          sourceMapFilename: 'tmp/maps/sourceMapURLFunction.css.map',
+          sourceMapURL: function (/* dest */) {
+            return '../maps/sourceMapURLFunction.css.map';
+          }
+        },
+        src: 'test/fixtures/style3.less',
+        dest: 'tmp/sourceMapURLFunction.css'
+      },
       sourceMapBasepath: {
         options: {
           sourceMap: true,

tasks/less.js

@@ -126,6 +126,14 @@ module.exports = function(grunt) {
       }
     }
 
+    if (typeof options.sourceMapURL === 'function') {
+      try {
+        options.sourceMapURL = options.sourceMapURL(destFile);
+      } catch (e) {
+        grunt.fail.warn(wrapError(e, 'Generating sourceMapURL failed.'));
+      }
+    }
+
     if (typeof options.sourceMap === 'boolean' && options.sourceMap) {
       options.sourceMap = {
         sourceMapBasepath: options.sourceMapBasepath,

test/less_test.js

@@ -135,6 +135,13 @@ exports.less = {
     test.ok(actual.indexOf('/*# sourceMappingURL=custom/url/for/sourceMap.css.map') !== -1, 'compiled file should have a custom source map URL.');
     test.done();
   },
+  sourceMapURLFunction: function(test) {
+    test.expect(1);
+
+    var actual = read('tmp/sourceMapURLFunction.css');
+    test.ok(actual.indexOf('/*# sourceMappingURL=../maps/sourceMapURLFunction.css.map') !== -1, 'compiled file should have a dynamic source map URL.');
+    test.done();
+  },
   sourceMapBasepath: function(test) {
     test.expect(1);