Implement SASS_PATH

- New function buildIncludePaths to build the includePaths string for passing through to libsass
- In buildIncludePaths, check for SASS_PATH environment variable, and if found include them behind any other specified include-paths
- Add two tests to `.render(options, callback)`:
  - "should check SASS_PATH in the specified order"
  - "should prefer include path over SASS_PATH"

lib/index.js

@@ -16,7 +16,6 @@ if (!sass.hasBinary(sass.getBinaryPath())) {
   }
 }
 
-
 /**
  * Require binding
  */
@@ -165,6 +164,26 @@ function getLinefeed(options) {
 }
 
 /**
+ * Build an includePaths string
+ * from the options.includePaths array and the SASS_PATH environment variable
+ *
+ * @param {Object} options
+ * @api private
+ */
+
+function buildIncludePaths(options) {
+  options.includePaths = options.includePaths || [];
+
+  if (process.env.hasOwnProperty('SASS_PATH')) {
+    options.includePaths = options.includePaths.concat(
+      process.env.SASS_PATH.split(path.delimiter)
+    );
+  }
+
+  return options.includePaths.join(path.delimiter);
+}
+
+/**
  * Get options
  *
  * @param {Object} options
@@ -173,12 +192,13 @@ function getLinefeed(options) {
 
 function getOptions(opts, cb) {
   var options = clonedeep(opts || {});
+
   options.sourceComments = options.sourceComments || false;
   if (options.hasOwnProperty('file')) {
     options.file = getInputFile(options);
   }
   options.outFile = getOutputFile(options);
-  options.includePaths = (options.includePaths || []).join(path.delimiter);
+  options.includePaths = buildIncludePaths(options);
   options.precision = parseInt(options.precision) || 5;
   options.sourceMap = getSourceMap(options);
   options.style = getStyle(options);

test/api.js

@@ -14,6 +14,11 @@ var assert = require('assert'),
 describe('api', function() {
 
   describe('.render(options, callback)', function() {
+
+    beforeEach(function() {
+      delete process.env.SASS_PATH;
+    });
+
     it('should compile sass to css with file', function(done) {
       var expected = read(fixture('simple/expected.css'), 'utf8').trim();
 
@@ -137,6 +142,59 @@ describe('api', function() {
       });
     });
 
+    it('should check SASS_PATH in the specified order', function(done) {
+      var src = read(fixture('sass-path/index.scss'), 'utf8');
+      var expectedRed = read(fixture('sass-path/expected-red.css'), 'utf8').trim();
+      var expectedOrange = read(fixture('sass-path/expected-orange.css'), 'utf8').trim();
+
+      envIncludes = [
+        fixture('sass-path/red'),
+        fixture('sass-path/orange')
+      ];
+
+      process.env.SASS_PATH = envIncludes.join(path.delimiter);
+      sass.render({
+        data: src,
+        includePaths: []
+      }, function(error, result) {
+        assert.equal(result.css.toString().trim(), expectedRed.replace(/\r\n/g, '\n'));
+      });
+
+      process.env.SASS_PATH = envIncludes.reverse().join(path.delimiter);
+      sass.render({
+        data: src,
+        includePaths: []
+      }, function(error, result) {
+        assert.equal(result.css.toString().trim(), expectedOrange.replace(/\r\n/g, '\n'));
+        done();
+      });
+    });
+
+    it('should prefer include path over SASS_PATH', function(done) {
+      var src = read(fixture('sass-path/index.scss'), 'utf8');
+      var expectedRed = read(fixture('sass-path/expected-red.css'), 'utf8').trim();
+      var expectedOrange = read(fixture('sass-path/expected-orange.css'), 'utf8').trim();
+
+      envIncludes = [
+        fixture('sass-path/red')
+      ];
+      process.env.SASS_PATH = envIncludes.join(path.delimiter);
+
+      sass.render({
+        data: src,
+        includePaths: []
+      }, function(error, result) {
+        assert.equal(result.css.toString().trim(), expectedRed.replace(/\r\n/g, '\n'));
+      });
+      sass.render({
+        data: src,
+        includePaths: [fixture('sass-path/orange')]
+      }, function(error, result) {
+        assert.equal(result.css.toString().trim(), expectedOrange.replace(/\r\n/g, '\n'));
+        done();
+      });
+    });
+
     it('should render with precision option', function(done) {
       var src = read(fixture('precision/index.scss'), 'utf8');
       var expected = read(fixture('precision/expected.css'), 'utf8').trim();

test/fixtures/sass-path/expected-orange.css

+body {
+  background: orange; }
+

test/fixtures/sass-path/expected-red.css

+body {
+  background: red; }
+

test/fixtures/sass-path/index.scss

+@import 'colors';
+
+body {
+  background: $color;
+}
+

test/fixtures/sass-path/orange/colors.scss

+$color: orange;

test/fixtures/sass-path/red/colors.scss

+$color: red;