add option to skip compilation if no files in gulp stream

Author: brendankenny

README.md

@@ -245,6 +245,29 @@ gulp.task('js-compile', function () {
 });
 ```
 
+### Requiring gulp.src files for compilation
+By default, the gulp plugin will run the compiler even if no input is streamed in via `gulp.src`.
+To disable this behavior, users can specify a { requireStreamInput: true } argument to skip
+compilation if no files are streamed in. This allows interoperation with gulp plugins that signal
+through empty streams.
+
+```js
+var closureCompiler = require('google-closure-compiler').gulp({
+  requireStreamInput: true
+});
+var newer = require('gulp-newer');
+
+gulp.task('js-compile', function () {
+  return gulp.src('./src/js/**/*.js', {base: './'})
+      .pipe(newer('./dist/output.min.js'))
+      .pipe(closureCompiler({
+          compilation_level: 'ADVANCED',
+          js_output_file: 'output.min.js'
+        }))
+      .pipe(gulp.dest('./dist'));
+});
+```
+
 ### Gulp Sourcemaps
 The gulp plugin supports gulp sourcemaps.
 

lib/gulp/index.js

@@ -30,9 +30,10 @@
 
 
 /**
+ * @param {Object<string,string>} initOptions
  * @return {function(Object<string,string>|Array<string>):Object}
  */
-module.exports = function() {
+module.exports = function(initOptions) {
   var filesToJson = require('./concat-to-json');
   var jsonToVinyl = require('./json-to-vinyl');
   var Compiler = require('../node/closure-compiler');
@@ -41,6 +42,7 @@ module.exports = function() {
   var through = require('through2');
   /** @const */
   var PLUGIN_NAME = 'gulp-google-closure-compiler';
+  var streamInputRequired = initOptions ? !!initOptions.requireStreamInput : false;
 
   return function (compilationOptions, pluginOptions) {
     pluginOptions = pluginOptions || {};
@@ -76,6 +78,13 @@ module.exports = function() {
         // Input files are present. Convert them to a JSON encoded string
         stdInData = filesToJson(fileList);
       } else {
+        // If files in the stream were required, no compilation needed here.
+        if (streamInputRequired) {
+          this.emit('end');
+          cb();
+          return;
+        }
+
         // The compiler will always expect something on standard-in. So pass it an empty
         // list if no files were piped into this plugin.
         stdInData = "[]";

test/gulp.js

@@ -260,6 +260,40 @@ describe('gulp-google-closure-compiler', function() {
 
       stream.end();
     });
+
+    it('should compile gulp.src files when stream input is required', function(done) {
+      this.timeout(30000);
+      this.slow(10000);
+
+      var streamRequiredCompiler = compilerPackage.gulp({
+        requireStreamInput: true
+      });
+
+      gulp.src(__dirname + '/fixtures/**.js')
+          .pipe(streamRequiredCompiler({
+            compilation_level: 'SIMPLE',
+            warning_level: 'VERBOSE'
+          }))
+          .pipe(assert.length(1))
+          .pipe(assert.first(function(f) {
+            f.contents.toString().should.eql('function log(a){console.log(a)}log("one.js");log("two.js");\n');
+          }))
+          .pipe(assert.end(done));
+    });
+
+    it('should generate no output without gulp.src files when stream input is required', function(done) {
+      var streamRequiredCompiler = compilerPackage.gulp({
+        requireStreamInput: true
+      });
+
+      gulp.src([])
+          .pipe(streamRequiredCompiler({
+            compilation_level: 'SIMPLE',
+            warning_level: 'VERBOSE'
+          }))
+          .pipe(assert.length(0))
+          .pipe(assert.end(done));
+    });
   });
 
   describe('in streaming mode', function() {