Buffer stores a is modified on disk flag

spec/app/buffer-spec.coffee

@@ -90,6 +90,21 @@ describe 'Buffer', ->
           expect(event.newText).toBe "second"
           expect(buffer.isModified()).toBeFalsy()
 
+    describe "when the buffer is modified", ->
+      it "sets modifiedOnDisk to be true", ->
+        fileChangeHandler = jasmine.createSpy('fileChange')
+        buffer.file.on 'contents-change', fileChangeHandler
+
+        buffer.insert([0, 0], "a change")
+        fs.write(path, "second")
+
+        expect(fileChangeHandler.callCount).toBe 0
+        waitsFor "file to trigger contents-change event", ->
+          fileChangeHandler.callCount > 0
+
+        runs ->
+          expect(buffer.isModifiedOnDisk()).toBeTruthy()
+
   describe ".isModified()", ->
     beforeEach ->
       buffer.destroy()

src/app/buffer.coffee

@@ -12,6 +12,7 @@ class Buffer
   @idCounter = 1
   undoManager: null
   modified: null
+  modifiedOnDisk: null
   lines: null
   file: null
 
@@ -41,7 +42,9 @@ class Buffer
     @file?.off()
     @file = new File(path)
     @file.on "contents-change", =>
-      unless @isModified()
+      if @isModified()
+        @modifiedOnDisk = true
+      else
         @setText(fs.read(@file.getPath()))
         @modified = false
     @trigger "path-change", this
@@ -167,9 +170,13 @@ class Buffer
     fs.write path, @getText()
     @file?.updateMd5()
     @modified = false
+    @modifiedOnDisk = false
     @setPath(path)
     @trigger 'after-save'
 
+  isModifiedOnDisk: ->
+    @modifiedOnDisk
+
   isModified: ->
     @modified