chore(gulp): Skip Dart tasks when the SDK is not detected

fixes #268

gulpfile.js

@@ -13,6 +13,7 @@ var readline = require('readline');
 var runSequence = require('run-sequence');
 var spawn = require('child_process').spawn;
 var through2 = require('through2');
+var which = require('which');
 
 var js2es5Options = {
   sourceMaps: true,
@@ -41,7 +42,35 @@ var js2dartOptions = {
   outputLanguage: 'dart'
 };
 
-var PUB_CMD = process.platform === 'win32' ? 'pub.bat' : 'pub';
+var DART_SDK = false;
+
+try {
+  which.sync('dart');
+  console.log('Dart SDK detected');
+  if (process.platform === 'win32') {
+    DART_SDK = {
+      PUB: 'pub.bat',
+      ANALYZER: 'dartanalyzer.bat'
+    };
+  } else {
+    DART_SDK = {
+      PUB: 'pub',
+      ANALYZER: 'dartanalyzer'
+    };
+  }
+} catch (e) {
+  console.log('Dart SDK is not available, Dart tasks will be skipped.');
+  var gulpTaskFn = gulp.task.bind(gulp);
+  gulp.task = function (name, deps, fn) {
+    if (name.indexOf('.dart') === -1) {
+      return gulpTaskFn(name, deps, fn);
+    } else {
+      return gulpTaskFn(name, function() {
+        console.log('Dart SDK is not available. Skipping task: ' + name);
+      });
+    }
+  };
+}
 
 var gulpTraceur = require('./tools/transpiler/gulp-traceur');
 
@@ -105,7 +134,7 @@ gulp.task('modules/build.dart/pubspec', function() {
   return streamToPromise(changedStream)
     .then(function() {
       return Q.all(files.map(function(file) {
-        return processToPromise(spawn(PUB_CMD, ['get'], {
+        return processToPromise(spawn(DART_SDK.PUB, ['get'], {
           stdio: 'inherit',
           cwd: path.dirname(file)
         }));
@@ -178,7 +207,7 @@ function createModuleTask(sourceTypeConfig) {
 // ------------------
 // ANALYZE
 
-gulp.task('analyze/dartanalyzer', function(done) {
+gulp.task('analyze/analyzer.dart', function(done) {
   var pubSpecs = [].slice.call(glob.sync('build/dart/*/pubspec.yaml', {
     cwd: __dirname
   }));
@@ -205,8 +234,7 @@ gulp.task('analyze/dartanalyzer', function(done) {
   }));
 
   function analyze(dirName, done) {
-    var dartanalyzerCmd = (process.platform === "win32" ? "dartanalyzer.bat" : "dartanalyzer");
-    var stream = spawn(dartanalyzerCmd, ['--fatal-warnings', tempFile], {
+    var stream = spawn(DART_SDK.ANALYZER, ['--fatal-warnings', tempFile], {
       // inherit stdin and stderr, but filter stdout
       stdio: [process.stdin, 'pipe', process.stderr],
       cwd: dirName
@@ -348,7 +376,7 @@ gulp.task('serve', function() {
 });
 
 gulp.task('examples/pub.serve', function(done) {
-  spawn(PUB_CMD, ['serve'], {cwd: 'build/dart/examples', stdio: 'inherit'})
+  spawn(DART_SDK.PUB, ['serve'], {cwd: 'build/dart/examples', stdio: 'inherit'})
     .on('done', done);
 });
 
@@ -364,10 +392,10 @@ gulp.task('build', function(done) {
     // parallel
     ['jsRuntime/build', 'modules/build.dart', 'modules/build.dev.js'],
     // sequential
-    'analyze/dartanalyzer'
+    'analyze/analyzer.dart'
   );
 });
 
 gulp.task('analyze', function(done) {
-  runSequence('analyze/dartanalyzer');
+  runSequence('analyze/analyzer.dart');
 });

package.json

@@ -8,30 +8,31 @@
   "author": "Tobias Bosch <tbosch@google.com>",
   "license": "Apache-2.0",
   "dependencies": {
-    "es6-module-loader": "^0.9.2",
-    "systemjs": "^0.9.1",
     "angular-benchpress": "^0.1.3",
-    "karma-cli": "^0.0.4",
+    "es6-module-loader": "^0.9.2",
+    "event-stream": "^3.1.5",
+    "glob": "^4.0.6",
+    "gulp-connect": "~1.0.5",
+    "gulp-rimraf": "^0.1.0",
     "karma": "^0.12.23",
     "karma-chrome-launcher": "^0.1.4",
+    "karma-cli": "^0.0.4",
     "karma-dart": "^0.2.8",
     "karma-jasmine": "^0.2.2",
     "merge": "^1.2.0",
     "q": "^1.0.1",
-    "through2": "^0.6.1",
-    "event-stream": "^3.1.5",
-    "gulp-connect": "~1.0.5",
-    "gulp-rimraf": "^0.1.0",
     "run-sequence": "^0.3.6",
-    "glob": "^4.0.6",
-    "traceur": "0.0.74"
+    "systemjs": "^0.9.1",
+    "through2": "^0.6.1",
+    "traceur": "0.0.74",
+    "which": "~1"
   },
   "devDependencies": {
     "gulp": "^3.8.8",
     "gulp-changed": "^1.0.0",
-    "gulp-rename": "^1.2.0",
-    "gulp-shell": "^0.2.10",
+    "gulp-ejs": "^0.3.1",
     "gulp-load-plugins": "^0.7.1",
-    "gulp-ejs": "^0.3.1"
+    "gulp-rename": "^1.2.0",
+    "gulp-shell": "^0.2.10"
   }
 }