Merge cursors after buffer changes, but not after movement

spec/atom/editor-spec.coffee

@@ -769,6 +769,24 @@ describe "Editor", ->
       expect(cursor2.position()).toEqual(top: 6 * editor.lineHeight, left: 0)
       expect(cursor2.getBufferPosition()).toEqual [6, 0]
 
+    it "consolidates cursors when they overlap", ->
+      editor.setCursorScreenPosition([0, 0])
+      editor.addCursorAtScreenPosition([0, 1])
+      editor.addCursorAtScreenPosition([1, 1])
+
+      [cursor1, cursor2, cursor3] = editor.compositeCursor.getCursors()
+      expect(editor.compositeCursor.getCursors().length).toBe 3
+
+      editor.backspace()
+      expect(editor.compositeCursor.getCursors().length).toBe 2
+      expect(cursor1.getBufferPosition()).toEqual [0,0]
+      expect(cursor3.getBufferPosition()).toEqual [1,0]
+      expect(cursor2.parent().length).toBe 0
+
+      editor.insertText "x"
+      expect(editor.lineForBufferRow(0)).toBe "xar quicksort = function () {"
+      expect(editor.lineForBufferRow(1)).toBe "x var sort = function(items) {"
+
     describe "inserting text", ->
       describe "when cursors are on the same line", ->
         describe "when inserting newlines", ->

src/atom/composite-cursor.coffee

@@ -1,4 +1,5 @@
 Cursor = require 'cursor'
+_ = require 'underscore'
 
 module.exports =
 class CompositeCursor
@@ -20,15 +21,15 @@ class CompositeCursor
     cursor = @addCursor()
     cursor.setScreenPosition(screenPosition)
 
+  removeCursor: (cursor) ->
+    _.remove(@cursors, cursor)
+
   setScreenPosition: (screenPosition) ->
     cursor.setScreenPosition(screenPosition) for cursor in @cursors
 
   getScreenPosition: ->
     @cursors[0].getScreenPosition()
 
-  handleBufferChange: (e) ->
-    cursor.handleBufferChange(e) for cursor in @cursors
-
   moveLeft: ->
     cursor.moveLeft() for cursor in @cursors
 
@@ -40,3 +41,16 @@ class CompositeCursor
 
   moveDown: ->
     cursor.moveDown() for cursor in @cursors
+
+  handleBufferChange: (e) ->
+    cursor.handleBufferChange(e) for cursor in @cursors
+    @mergeCursors()
+
+  mergeCursors: ->
+    positions = []
+    for cursor in new Array(@cursors...)
+      position = cursor.getBufferPosition().toString()
+      if position in positions
+        cursor.remove()
+      else
+        positions.push(position)

src/atom/composite-selection.coffee

@@ -1,19 +1,27 @@
 Selection = require 'selection'
+_ = require 'underscore'
 
 module.exports =
 class CompositeSeleciton
   constructor: (@editor) ->
     @selections = []
 
-  getSelections: -> @selections
+  getSelections: -> new Array(@selections...)
 
   addSelectionForCursor: (cursor) ->
     selection = new Selection({@editor, cursor})
     @selections.push(selection)
     @editor.lines.append(selection)
 
+  removeSelectionForCursor: (cursor) ->
+    _.remove(@selections, @selectionForCursor(cursor))
+
+  selectionForCursor: (cursor) ->
+    _.find @selections, (selection) -> selection.cursor == cursor
+
   insertText: (text) ->
     selection.insertText(text) for selection in @selections
 
   backspace: ->
-    selection.backspace() for selection in @selections
+    for selection in @getSelections()
+      selection.backspace()

src/atom/cursor.coffee

@@ -30,6 +30,11 @@ class Cursor extends View
 
     @setBufferPosition([newRow, newColumn])
 
+  remove: ->
+    @editor.compositeCursor.removeCursor(this)
+    @editor.compositeSelection.removeSelectionForCursor(this)
+    super()
+
   setScreenPosition: (position, options={}) ->
     position = Point.fromObject(position)
     clip = options.clip ? true

src/atom/point.coffee

@@ -74,3 +74,5 @@ class Point
   inspect: ->
     "(#{@row}, #{@column})"
 
+  toString: ->
+    "#{@row},#{@column}"