Handle shebang in ScriptFileStorage load/save

Before this change, ScriptFileStorage.load was returning source code
including shebang (#!/usr/bin/node). This prevented the front-end
from matching the file on disk with the script loaded in Node/V8.
As a result, `node-debug _mocha` did not show the breakpoint in
the _mocha file.

ScriptFileStorage.save is preserving shebang when saving the updated
file now, so that live edit works as expected.

lib/ScriptFileStorage.js

@@ -37,9 +37,18 @@ $class.save = function(path, content, callback) {
     return;
   }
   var newSource = match[1];
-  fs.writeFile(path, newSource, function(err) {
-    callback(err);
-  });
+  async.waterfall([
+    fs.readFile.bind(fs, path, 'utf-8'),
+
+    function(oldContent, cb) {
+      var match = /^(\#\!.*)/.exec(oldContent);
+      if (match)
+        newSource = match[1] + newSource;
+
+      fs.writeFile(path, newSource, cb);
+    }
+  ],
+  callback);
 };
 
 /**
@@ -52,6 +61,10 @@ $class.load = function(path, callback) {
     { encoding: 'utf-8' },
     function(err, content) {
       if (err) return callback(err);
+
+      // remove shebang
+      content = content.replace(/^\#\!.*/, '');
+
       var source = MODULE_HEADER + content + MODULE_TRAILER;
       return callback(null, source);
     }

test/ScriptFileStorage.js

@@ -30,6 +30,21 @@ describe('ScriptFileStorage', function() {
     });
   });
 
+  it('preserves shebang when saving new content', function(done) {
+    runLiveEdit(
+      function(content) { return '#!/usr/bin/node\n' + content; },
+      function(debuggerClient, originalScript, runtimeScript) {
+        var storage = new ScriptFileStorage();
+        storage.save(TEMP_FILE, edited(runtimeScript), function(err) {
+          if (err) throw err;
+          var newScript = fs.readFileSync(TEMP_FILE, { encoding: 'utf-8' });
+          expect(newScript).to.equal(edited(originalScript));
+          done();
+        });
+      }
+    );
+  });
+
   it('loads content with node.js module wrapper', function(done) {
     fs.writeFileSync(TEMP_FILE, '/* content */');
     storage.load(TEMP_FILE, function(err, content) {
@@ -40,6 +55,16 @@ describe('ScriptFileStorage', function() {
     });
   });
 
+  it('loads content without shebang', function(done) {
+    fs.writeFileSync(TEMP_FILE, '#!/usr/bin/env/node\n/* content */');
+    storage.load(TEMP_FILE, function(err, content) {
+      if (err) throw err;
+      expect(content).to.not.contain('#!');
+      expect(content).to.contain('/* content */');
+      done();
+    });
+  });
+
   it('finds application root for subdir/app.js by checking package.json file in parent',
     function(done) {
       givenTempFiles('subdir/', 'subdir/app.js', 'package.json');
@@ -217,8 +242,13 @@ describe('ScriptFileStorage', function() {
     return source.replace(';', '; /* edited */');
   }
 
-  function runLiveEdit(callback) {
-    var originalScript = createTempFileAsCopyOf('LiveEdit.js');
+  function runLiveEdit(transformSource, callback) {
+    if (!callback) {
+      callback = transformSource;
+      transformSource = null;
+    }
+
+    var originalScript = createTempFileAsCopyOf('LiveEdit.js', transformSource);
     launcher.startDebugger(TEMP_FILE, function(childProcess, debuggerClient) {
       getScriptSourceByName(debuggerClient, TEMP_FILE, function(source) {
         callback(debuggerClient, originalScript, source);
@@ -226,9 +256,10 @@ describe('ScriptFileStorage', function() {
     });
   }
 
-  function createTempFileAsCopyOf(fixture) {
+  function createTempFileAsCopyOf(fixture, transform) {
     var sourcePath = path.join(__dirname, 'fixtures', fixture);
     var content = fs.readFileSync(sourcePath, { encoding: 'utf-8' });
+    if (transform) content = transform(content);
     fs.writeFileSync(TEMP_FILE, content);
     return content;
   }