Importer: Ability to return value.

Feature suggested by @jhnns.

lib/index.js

@@ -176,12 +176,18 @@ function getOptions(options) {
 
   if (importer) {
     options.importer = function(file, prev, key) {
-      importer(file, prev, function(data) {
+      var done = function(data) {
         binding.importedCallback({
           index: key,
           objectLiteral: data
         });
-      });
+      };
+
+      var result = importer(file, prev, done);
+
+      if (result) {
+        done(result);
+      }
     };
   }
 

test/api.js

@@ -133,7 +133,7 @@ describe('api', function() {
       });
     });
 
-    it('should override imports with custom importer with data', function(done) {
+    it('should override imports with custom importer with "data" as input and uses callback', function(done) {
       var src = read(fixture('include-files/index.scss'), 'utf8');
 
       sass.render({
@@ -151,7 +151,7 @@ describe('api', function() {
       });
     });
 
-    it('should override imports with custom importer with file', function(done) {
+    it('should override imports with custom importer with "file" as input and uses callback', function(done) {
       sass.render({
         file: fixture('include-files/index.scss'),
         success: function(result) {
@@ -166,6 +166,40 @@ describe('api', function() {
         }
       });
     });
+
+    it('should override imports with custom importer with "data" as input and returns value', function(done) {
+      var src = read(fixture('include-files/index.scss'), 'utf8');
+
+      sass.render({
+        data: src,
+        success: function(result) {
+          assert.equal(result.css.trim(), 'div {\n  color: yellow; }\n\ndiv {\n  color: yellow; }');
+          done();
+        },
+        importer: function(url, prev) {
+          return {
+            file: prev + url,
+            contents: 'div {color: yellow;}'
+          };
+        }
+      });
+    });
+
+    it('should override imports with custom importer with "file" as input and returns value', function(done) {
+      sass.render({
+        file: fixture('include-files/index.scss'),
+        success: function(result) {
+          assert.equal(result.css.trim(), 'div {\n  color: yellow; }\n\ndiv {\n  color: yellow; }');
+          done();
+        },
+        importer: function(url, prev) {
+          return {
+            file: prev + url,
+            contents: 'div {color: yellow;}'
+          };
+        }
+      });
+    });
   });
 
   describe('.renderSync(options)', function() {
@@ -206,7 +240,7 @@ describe('api', function() {
       done();
     });
 
-    it('should override imports with custom importer with data', function(done) {
+    it('should override imports with custom importer with "data" as input and uses callback', function(done) {
       var src = read(fixture('include-files/index.scss'), 'utf8');
 
       var result = sass.renderSync({
@@ -223,7 +257,7 @@ describe('api', function() {
       done();
     });
 
-    it('should override imports with custom importer with file', function(done) {
+    it('should override imports with custom importer with "file" as input and uses callback', function(done) {
       var result = sass.renderSync({
         file: fixture('include-files/index.scss'),
         importer: function(url, prev, finish) {
@@ -237,6 +271,38 @@ describe('api', function() {
       assert.equal(result.css.trim(), 'div {\n  color: yellow; }\n\ndiv {\n  color: yellow; }');
       done();
     });
+
+    it('should override imports with custom importer with "data" as input and returns value', function(done) {
+      var src = read(fixture('include-files/index.scss'), 'utf8');
+
+      var result = sass.renderSync({
+        data: src,
+        importer: function(url, prev) {
+          return {
+            file: prev + url,
+            contents: 'div {color: yellow;}'
+          };
+        }
+      });
+
+      assert.equal(result.css.trim(), 'div {\n  color: yellow; }\n\ndiv {\n  color: yellow; }');
+      done();
+    });
+
+    it('should override imports with custom importer with "file" as input and returns value', function(done) {
+      var result = sass.renderSync({
+        file: fixture('include-files/index.scss'),
+        importer: function(url, prev) {
+          return {
+            file: prev + url,
+            contents: 'div {color: yellow;}'
+          };
+        }
+      });
+
+      assert.equal(result.css.trim(), 'div {\n  color: yellow; }\n\ndiv {\n  color: yellow; }');
+      done();
+    });
   });
 
   describe('.render({stats: {}})', function() {