Use Editor.abort to clear autocomplete's buffer changes on cancel

Using this new `abort` mechanism ensures that autocomplete's changes can never be redone, while eliminating the need to track operation counts explicitly.

src/app/editor.coffee

@@ -246,6 +246,9 @@ class Editor extends View
   paste: -> @activeEditSession.pasteText()
   undo: -> @activeEditSession.undo()
   redo: -> @activeEditSession.redo()
+  transact: (fn) -> @activeEditSession.transact(fn)
+  commit: -> @activeEditSession.commit()
+  abort: -> @activeEditSession.abort()
   createFold: (startRow, endRow) -> @activeEditSession.createFold(startRow, endRow)
   foldCurrentRow: -> @activeEditSession.foldCurrentRow()
   unfoldCurrentRow: -> @activeEditSession.unfoldCurrentRow()

src/packages/autocomplete/spec/autocomplete-spec.coffee

@@ -223,6 +223,19 @@ describe "Autocomplete", ->
       expect(editor.lineForBufferRow(10)).toBe "extra:S:extra"
       expect(editor.getCursorBufferPosition()).toEqual [10,7]
 
+    it "restores the original buffer contents even if there was an additional operation after autocomplete attached (regression)", ->
+      editor.getBuffer().insert([10,0] ,"extra:s:extra")
+      editor.setCursorBufferPosition([10,7])
+      autocomplete.attach()
+
+      editor.getBuffer().append('hi')
+      expect(editor.lineForBufferRow(10)).toBe "extra:sort:extra"
+      autocomplete.trigger 'core:cancel'
+      expect(editor.lineForBufferRow(10)).toBe "extra:s:extra"
+
+      editor.redo()
+      expect(editor.lineForBufferRow(10)).toBe "extra:s:extra"
+
   describe 'move-up event', ->
     it "highlights the previous match and replaces the selection with it", ->
       editor.getBuffer().insert([10,0] ,"extra:t:extra")

src/packages/autocomplete/src/autocomplete.coffee

@@ -17,7 +17,6 @@ class Autocomplete extends SelectList
   originalSelectionBufferRange: null
   originalCursorPosition: null
   aboveCursor: false
-  undoCount: 0
   filterKey: 'word'
 
   initialize: (@editor) ->
@@ -75,14 +74,15 @@ class Autocomplete extends SelectList
     @editor.setCursorBufferPosition([position.row, position.column + match.suffix.length])
 
   cancelled: ->
-    @editor.undo() for undo in [0...@undoCount]
+    @editor.abort()
     @editor.setSelectedBufferRange(@originalSelectionBufferRange)
 
     @miniEditor.setText('')
     @editor.rootView()?.focus() if @miniEditor.isFocused
 
   attach: ->
-    @undoCount = 0
+    @editor.transact()
+
     @aboveCursor = false
     @originalSelectionBufferRange = @editor.getSelection().getBufferRange()
     @originalCursorPosition = @editor.getCursorScreenPosition()
@@ -133,13 +133,12 @@ class Autocomplete extends SelectList
     selection = @editor.getSelection()
     startPosition = selection.getBufferRange().start
     buffer = @editor.getBuffer()
-    @editor.activeEditSession.transact =>
-      selection.deleteSelectedText()
-      cursorPosition = @editor.getCursorBufferPosition()
-      buffer.delete(Range.fromPointWithDelta(cursorPosition, 0, match.suffix.length))
-      buffer.delete(Range.fromPointWithDelta(cursorPosition, 0, -match.prefix.length))
-      @editor.insertText(match.word)
-    @undoCount++
+
+    selection.deleteSelectedText()
+    cursorPosition = @editor.getCursorBufferPosition()
+    buffer.delete(Range.fromPointWithDelta(cursorPosition, 0, match.suffix.length))
+    buffer.delete(Range.fromPointWithDelta(cursorPosition, 0, -match.prefix.length))
+    @editor.insertText(match.word)
 
     infixLength = match.word.length - match.prefix.length - match.suffix.length
     @editor.setSelectedBufferRange([startPosition, [startPosition.row, startPosition.column + infixLength]])