Add EditSession.transact and friends

`EditSession.transact` adds more semantics on top of `UndoManager`'s
version pertaining to restoring selections on undo/redo of the
transaction.

src/app/buffer.coffee

@@ -224,14 +224,11 @@ class Buffer
     else
       operation.do()
 
-  transact: (fn) ->
-    @undoManager.transact(fn)
-
-  undo: (editSession) ->
-    @undoManager.undo(editSession)
-
-  redo: (editSession) ->
-    @undoManager.redo(editSession)
+  transact: (fn) ->  @undoManager.transact(fn)
+  undo: (editSession) -> @undoManager.undo(editSession)
+  redo: (editSession) -> @undoManager.redo(editSession)
+  commit: -> @undoManager.commit()
+  abort: -> @undoManager.abort()
 
   save: ->
     @saveAs(@getPath()) if @isModified()

src/app/edit-session.coffee

@@ -235,6 +235,27 @@ class EditSession
   redo: ->
     @buffer.redo(this)
 
+  transact: (fn) ->
+    isNewTransaction = @buffer.transact()
+    console.log isNewTransaction
+    oldSelectedRanges = @getSelectedBufferRanges()
+    @pushOperation
+      undo: (editSession) ->
+        editSession?.setSelectedBufferRanges(oldSelectedRanges)
+    if fn
+      fn()
+      @commit() if isNewTransaction
+
+  commit: ->
+    newSelectedRanges = @getSelectedBufferRanges()
+    @pushOperation
+      redo: (editSession) ->
+        editSession?.setSelectedBufferRanges(newSelectedRanges)
+    @buffer.commit()
+
+  abort: ->
+    @buffer.abort()
+
   foldAll: ->
     @displayBuffer.foldAll()
 
@@ -303,19 +324,6 @@ class EditSession
   mutateSelectedText: (fn) ->
     @transact => fn(selection) for selection in @getSelections()
 
-  transact: (fn) ->
-    @buffer.transact =>
-      oldSelectedRanges = @getSelectedBufferRanges()
-      @pushOperation
-        undo: (editSession) ->
-          editSession?.setSelectedBufferRanges(oldSelectedRanges)
-
-      fn()
-      newSelectedRanges = @getSelectedBufferRanges()
-      @pushOperation
-        redo: (editSession) ->
-          editSession?.setSelectedBufferRanges(newSelectedRanges)
-
   pushOperation: (operation) ->
     @buffer.pushOperation(operation, this)
 

src/app/undo-manager.coffee

@@ -29,13 +29,14 @@ class UndoManager
       @clear()
 
   transact: (fn) ->
-    shouldCommit = not @currentTransaction?
+    isNewTransaction = not @currentTransaction?
     @currentTransaction ?= []
     if fn
       try
         fn()
       finally
-        @commit() if shouldCommit
+        @commit() if isNewTransaction
+    isNewTransaction
 
   commit: ->
     @undoHistory.push(@currentTransaction) if @currentTransaction?.length