Add save alert when closing a modified buffer

spec/app/editor-spec.coffee

@@ -1690,8 +1690,9 @@ describe "Editor", ->
 
     describe "when buffer is modified", ->
       it "triggers alert and does not close session", ->
-        originalBuffer = editor.buffer
+        spyOn(editor, 'remove')
+        spyOn($native, 'alert')
         editor.insertText("I AM CHANGED!")
         editor.trigger "close"
-        expect(editor.buffer).toBe originalBuffer
-
+        expect(editor.remove).not.toHaveBeenCalled()
+        expect($native.alert).toHaveBeenCalled()

src/app/editor.coffee

@@ -7,6 +7,8 @@ Range = require 'range'
 EditSession = require 'edit-session'
 CursorView = require 'cursor-view'
 SelectionView = require 'selection-view'
+Native = require 'native'
+fs = require 'fs'
 
 $ = require 'jquery'
 _ = require 'underscore'
@@ -605,11 +607,13 @@ class Editor extends View
   save: ->
     if not @buffer.getPath()
       path = $native.saveDialog()
-      return if not path
+      return false if not path
       @buffer.saveAs(path)
     else
       @buffer.save()
 
+    true
+
   clipScreenPosition: (screenPosition, options={}) ->
     @renderer.clipScreenPosition(screenPosition, options)
 
@@ -784,8 +788,19 @@ class Editor extends View
 
   close: ->
     return if @mini
-    return if @buffer.isModified()
-    @removeActiveEditSession()
+    if @buffer.isModified()
+      filename = if @buffer.getPath() then fs.base(@buffer.getPath()) else "untitled buffer"
+      message = "'#{filename}' has changes, do you want to save them?"
+      detailedMessage = "Your changes will be lost if you don't save them"
+      buttons = [
+        ["Save", => @save() and @removeActiveEditSession()]
+        ["Cancel", =>]
+        ["Don't save", => @removeActiveEditSession()]
+      ]
+
+      Native.alert message, detailedMessage, buttons
+    else
+      @removeActiveEditSession()
 
   unsubscribeFromBuffer: ->
     @buffer.off ".editor#{@id}"