Support unsetting explicit grammar for path

spec/app/grammar-view-spec.coffee

@@ -0,0 +1,49 @@
+RootView = require 'root-view'
+GrammarView = require 'grammar-view'
+_ = require 'underscore'
+
+describe "GrammarView", ->
+  [editor, rootView, textGrammar, jsGrammar] =  []
+
+  beforeEach ->
+    path = require.resolve('fixtures/sample.js')
+    syntax.removeGrammarForPath(path)
+    rootView = new RootView(path)
+    editor = rootView.getActiveEditor()
+    rootView.attachToDom()
+    textGrammar = _.find syntax.grammars, (grammar) -> grammar.name is 'Plain Text'
+    expect(textGrammar).toBeTruthy()
+    jsGrammar = _.find syntax.grammars, (grammar) -> grammar.name is 'JavaScript'
+    expect(jsGrammar).toBeTruthy()
+    expect(editor.getGrammar()).toBe jsGrammar
+
+  afterEach ->
+    rootView.deactivate()
+
+  describe "when editor:select-grammar is toggled", ->
+    it "displays a list of all the available grammars", ->
+      editor.trigger 'editor:select-grammar'
+      grammarView = rootView.find('.grammar-view').view()
+      expect(grammarView).toExist()
+      grammars = syntax.grammars
+      expect(grammarView.list.children('li').length).toBe grammars.length + 1
+      expect(grammarView.list.children('li:first').text()).toBe 'Auto Detect'
+
+  describe "when a grammar is selected", ->
+    it "sets the new grammar on the editor", ->
+      editor.trigger 'editor:select-grammar'
+      grammarView = rootView.find('.grammar-view').view()
+      grammarView.confirmed(textGrammar)
+      expect(editor.getGrammar()).toBe textGrammar
+
+  describe "when auto-detect is selected", ->
+    it "restores the auto-detected grammar on the editor", ->
+      editor.trigger 'editor:select-grammar'
+      grammarView = rootView.find('.grammar-view').view()
+      grammarView.confirmed(textGrammar)
+      expect(editor.getGrammar()).toBe textGrammar
+
+      editor.trigger 'editor:select-grammar'
+      grammarView = rootView.find('.grammar-view').view()
+      grammarView.confirmed(grammarView.array[0])
+      expect(editor.getGrammar()).toBe jsGrammar

src/app/grammar-view.coffee

@@ -11,6 +11,7 @@ class GrammarView extends SelectList
   initialize: (@editor) ->
     @currentGrammar = @editor.getGrammar()
     @path = @editor.getPath()
+    @autoDetect = name: 'Auto Detect'
     requireStylesheet 'grammar-view.css'
     @command 'editor:select-grammar', =>
       @cancel()
@@ -30,7 +31,9 @@ class GrammarView extends SelectList
       @li grammar.name, class: grammarClass
 
   populate: ->
-    @setArray(syntax.grammars)
+    grammars = new Array(syntax.grammars...)
+    grammars.unshift(@autoDetect)
+    @setArray(grammars)
 
   cancelled: ->
     @miniEditor.setText('')
@@ -38,7 +41,10 @@ class GrammarView extends SelectList
 
   confirmed: (grammar) ->
     @cancel()
-    syntax.addGrammarForPath(@path, grammar)
+    if grammar is @autoDetect
+      syntax.removeGrammarForPath(@path)
+    else
+      syntax.addGrammarForPath(@path, grammar)
     @editor.reloadGrammar()
 
   attach: ->