Editor recalls cursor position and scroll state when a previously edited buffer is re-assigned.

spec/atom/editor-spec.coffee

@@ -894,6 +894,29 @@ describe "Editor", ->
     it "sets the cursor to the beginning of the file", ->
       expect(editor.getCursorScreenPosition()).toEqual(row: 0, column: 0)
 
+    it "recalls the cursor position and scroll position when the same buffer is re-assigned", ->
+      editor.attachToDom()
+      editor.height(editor.lineHeight * 5)
+      editor.width(editor.charWidth * 30)
+      editor.setCursorScreenPosition([8, 28])
+      advanceClock()
+
+      previousScrollTop = editor.scrollTop()
+      previousScrollLeft = editor.horizontalScroller.scrollLeft()
+
+      console.log "setting empty"
+      console.log editor.scrollTop()
+      editor.setBuffer(new Buffer)
+      expect(editor.getCursorScreenPosition()).toEqual [0, 0]
+      expect(editor.scrollTop()).toBe 0
+      expect(editor.horizontalScroller.scrollLeft()).toBe 0
+
+      console.log "setting back to buffer"
+      editor.setBuffer(buffer)
+      expect(editor.getCursorScreenPosition()).toEqual [8, 28]
+      expect(editor.scrollTop()).toBe previousScrollTop
+      expect(editor.horizontalScroller.scrollLeft()).toBe previousScrollLeft
+
   describe ".clipScreenPosition(point)", ->
     it "selects the nearest valid position to the given point", ->
       expect(editor.clipScreenPosition(row: 1000, column: 0)).toEqual(row: buffer.lastRow(), column: buffer.lineForRow(buffer.lastRow()).length)

src/atom/buffer.coffee

@@ -5,9 +5,11 @@ EventEmitter = require 'event-emitter'
 
 module.exports =
 class Buffer
+  @idCounter = 1
   lines: null
 
   constructor: (@path) ->
+    @id = @constructor.idCounter++
     @url = @path # we want this to be path on master, but let's not break it on a branch
     @lines = ['']
     if @path and fs.exists(@path)

src/atom/edit-session.coffee

@@ -0,0 +1,8 @@
+Point = require 'point'
+
+module.exports =
+class EditSession
+  cursorScreenPosition: new Point(0, 0)
+  scrollTop: 0
+  scrollLeft: 0
+

src/atom/editor.coffee

@@ -8,6 +8,7 @@ Point = require 'point'
 Range = require 'range'
 Selection = require 'selection'
 UndoManager = require 'undo-manager'
+EditSession = require 'edit-session'
 
 $ = require 'jquery'
 _ = require 'underscore'
@@ -40,6 +41,7 @@ class Editor extends View
   initialize: () ->
     requireStylesheet 'editor.css'
     requireStylesheet 'theme/twilight.css'
+    @editSessionsByBufferId = {}
     @bindKeys()
     @buildCursorAndSelection()
     @handleEvents()
@@ -154,17 +156,29 @@ class Editor extends View
     @screenLineCount() - 1
 
   setBuffer: (@buffer) ->
+    @saveEditSession() if @editSession
     document.title = @buffer.path
     @renderer = new Renderer(@buffer)
     @undoManager = new UndoManager(@buffer)
     @renderLines()
     @gutter.renderLineNumbers()
 
-    @setCursorScreenPosition(row: 0, column: 0)
+    @loadEditSessionForBuffer(@buffer)
 
     @buffer.on 'change', (e) => @cursor.bufferChanged(e)
     @renderer.on 'change', (e) => @handleRendererChange(e)
 
+  loadEditSessionForBuffer: (buffer) ->
+    @editSession = (@editSessionsByBufferId[buffer.id] ?= new EditSession)
+    @setCursorScreenPosition(@editSession.cursorScreenPosition)
+    @scrollTop(@editSession.scrollTop)
+    @horizontalScroller.scrollLeft(@editSession.scrollLeft)
+
+  saveEditSession: ->
+    @editSession.cursorScreenPosition = @getCursorScreenPosition()
+    @editSession.scrollTop = @scrollTop()
+    @editSession.scrollLeft = @horizontalScroller.scrollLeft()
+
   handleRendererChange: (e) ->
     { oldRange, newRange } = e
     unless newRange.isSingleLine() and newRange.coversSameRows(oldRange)