Radically simplify the definition of "modified" for buffers

Now, we maintain md5 signatures for the on-disk and in-memory contents of the buffer. Whenever either contents change, we recompute the signature and store it on the buffer. We can tell if the buffer is modified by comparing these signatures. When the disk contents change, we compare the memory and disk signatures *before* recomputing the disk signature to determine whether to update the buffer or mark it as a conflict.

spec/app/buffer-spec.coffee

@@ -77,7 +77,7 @@ describe 'Buffer', ->
       waitsFor "buffer path change", ->
         eventHandler.callCount > 0
 
-  describe "when the buffer's file is modified (via another process)", ->
+  describe "when the buffer's on-disk contents change (via another process writing to its file)", ->
     path = null
     beforeEach ->
       path = "/tmp/tmp.txt"
@@ -98,8 +98,8 @@ describe 'Buffer', ->
       runs ->
         expect(changeHandler).not.toHaveBeenCalled()
 
-    describe "when the buffer is unmodified", ->
-      it "triggers 'change' event and buffer remains unmodified", ->
+    describe "when the buffer's memory contents are the same as the *previous* disk contents", ->
+      it "changes the memory contents of the buffer to match the new disk contents and triggers a 'change' event", ->
         changeHandler = jasmine.createSpy('changeHandler')
         buffer.on 'change', changeHandler
         fs.write(path, "second")
@@ -116,8 +116,8 @@ describe 'Buffer', ->
           expect(event.newText).toBe "second"
           expect(buffer.isModified()).toBeFalsy()
 
-    describe "when the buffer is modified", ->
-      it "sets modifiedOnDisk to be true", ->
+    describe "when the buffer's memory contents differ from the *previous* disk contents", ->
+      it "leaves the buffer in a modified state (does not update its memory contents)", ->
         fileChangeHandler = jasmine.createSpy('fileChange')
         buffer.file.on 'contents-change', fileChangeHandler
 
@@ -129,7 +129,7 @@ describe 'Buffer', ->
           fileChangeHandler.callCount > 0
 
         runs ->
-          expect(buffer.isModifiedOnDisk()).toBeTruthy()
+          expect(buffer.isModified()).toBeTruthy()
 
   describe "when the buffer's file is deleted (via another process)", ->
     it "no longer has a path", ->
@@ -342,14 +342,13 @@ describe 'Buffer', ->
         expect(-> buffer.save()).toThrow()
 
   describe "reload()", ->
-    it "loads text from disk are sets @modified and @modifiedOnDisk to false", ->
-      buffer.modified = true
-      buffer.modifiedOnDisk = true
+    it "reloads current text from disk and clears any conflicts", ->
       buffer.setText("abc")
+      buffer.conflict = true
 
       buffer.reload()
-      expect(buffer.modifed).toBeFalsy()
-      expect(buffer.modifiedOnDisk).toBeFalsy()
+      expect(buffer.isModified()).toBeFalsy()
+      expect(buffer.isInConflict()).toBeFalsy()
       expect(buffer.getText()).toBe(fileContents)
 
   describe ".saveAs(path)", ->

spec/app/editor-spec.coffee

@@ -155,6 +155,7 @@ describe "Editor", ->
     it "closes active edit session and loads next edit session", ->
       editor.edit(rootView.project.buildEditSessionForPath())
       editSession = editor.activeEditSession
+      spyOn(editSession.buffer, 'isModified').andReturn false
       spyOn(editSession, 'destroy').andCallThrough()
       spyOn(editor, "remove").andCallThrough()
       editor.trigger "core:close"

src/app/buffer.coffee

@@ -8,14 +8,15 @@ UndoManager = require 'undo-manager'
 BufferChangeOperation = require 'buffer-change-operation'
 Anchor = require 'anchor'
 AnchorRange = require 'anchor-range'
+{hex_md5}  = require 'md5'
 
 module.exports =
 class Buffer
   @idCounter = 1
   undoManager: null
-  modified: null
-  contentOnDisk: null
-  modifiedOnDisk: null
+  diskContentSignature: null
+  memoryContentSignature: null
+  conflict: false
   lines: null
   file: null
   anchors: null
@@ -31,13 +32,19 @@ class Buffer
     if path
       throw "Path '#{path}' does not exist" unless fs.exists(path)
       @setPath(path)
-      @contentOnDisk = fs.read(@getPath())
-      @setText(@contentOnDisk)
+      @setText(fs.read(@getPath()))
+      @computeDiskContentSignature()
     else
       @setText('')
 
+    @computeMemoryContentSignature()
     @undoManager = new UndoManager(this)
-    @modified = false
+
+  computeDiskContentSignature: ->
+    @diskContentSignature = fs.md5ForPath(@getPath())
+
+  computeMemoryContentSignature: ->
+    @memoryContentSignature = hex_md5(@getText())
 
   destroy: ->
     throw new Error("Destroying buffer twice with path '#{@getPath()}'") if @destroyed
@@ -57,10 +64,12 @@ class Buffer
   subscribeToFile: ->
     @file.on "contents-change", =>
       if @isModified()
-        @modifiedOnDisk = true
+        @conflict = true
+        @computeDiskContentSignature()
+        @trigger "contents-change-on-disk"
       else
         @setText(fs.read(@file.getPath()))
-        @modified = false
+        @computeDiskContentSignature()
 
     @file.on "remove", =>
       @file = null
@@ -70,10 +79,7 @@ class Buffer
       @trigger "path-change", this
 
   reload: ->
-    @contentOnDisk = fs.read(@getPath())
-    @setText(@contentOnDisk)
-    @modified = false
-    @modifiedOnDisk = false
+    @setText(fs.read(@getPath()))
 
   getBaseName: ->
     @file?.getBaseName()
@@ -87,13 +93,7 @@ class Buffer
     @file?.off()
     @file = new File(path)
     @subscribeToFile()
-    @file.on "contents-change", =>
-      if @isModified()
-        @modifiedOnDisk = true
-        @trigger "contents-change-on-disk"
-      else
-        @setText(fs.read(@file.getPath()))
-        @modified = false
+
     @trigger "path-change", this
 
   getExtension: ->
@@ -209,7 +209,8 @@ class Buffer
 
   replaceLines: (startRow, endRow, newLines) ->
     @lines[startRow..endRow] = newLines
-    @modified = true
+    @computeMemoryContentSignature()
+    @conflict = false unless @isModified()
 
   pushOperation: (operation, editSession) ->
     if @undoManager
@@ -235,23 +236,14 @@ class Buffer
     @trigger 'before-save'
     fs.write path, @getText()
     @file?.updateMd5()
-    @modified = false
-    @modifiedOnDisk = false
     @setPath(path)
-    @contentOnDisk = @getText()
+    @computeDiskContentSignature()
     @trigger 'after-save'
 
-  isInConflict: ->
-    @isModified() and @isModifiedOnDisk()
-
-  isModifiedOnDisk: ->
-    @modifiedOnDisk
-
   isModified: ->
-    @modified
+    @memoryContentSignature != @diskContentSignature
 
-  contentDifferentOnDisk: ->
-    @contentOnDisk != @getText()
+  isInConflict: -> @conflict
 
   getAnchors: -> new Array(@anchors...)
 

src/app/status-bar.coffee

@@ -41,7 +41,7 @@ class StatusBar extends View
     @updateBufferModifiedText()
 
   updateBufferModifiedText: ->
-    if @buffer.isModified() and @buffer.contentDifferentOnDisk()
+    if @buffer.isModified()
       @bufferModified.text('*')
     else
       @bufferModified.text('')