Handle exceptions thrown during do/undo/redo

spec/app/undo-manager-spec.coffee

@@ -98,3 +98,57 @@ describe "UndoManager", ->
       undoManager.undo()
       expect(buffer.lineForRow(0)).not.toContain("foo")
 
+    it "records transactions that occur prior to an exception", ->
+      spyOn(console, 'error')
+      buffer.setText("jumpstreet")
+      undoManager.transact ->
+        buffer.insert([0,0], "3")
+        buffer.insert([0,0], "2")
+        throw new Error("problem")
+        buffer.insert([0,0], "2")
+
+      expect(console.error).toHaveBeenCalled()
+      expect(buffer.lineForRow(0)).toBe "23jumpstreet"
+      undoManager.undo()
+      expect(buffer.lineForRow(0)).toBe "jumpstreet"
+
+  describe "when a `do` operation throws an exception", ->
+    it "clears the stack", ->
+      spyOn(console, 'error')
+      buffer.setText("word")
+      class FailingOperation
+        do: -> throw new Error("I'm a bad do operation")
+
+      buffer.insert([0,0], "1")
+      undoManager.pushOperation(new FailingOperation())
+      expect(console.error).toHaveBeenCalled()
+      undoManager.undo()
+      expect(buffer.lineForRow(0)).toBe "1word"
+
+
+  describe "when an `undo` operation throws an exception", ->
+    it "clears the stack", ->
+      spyOn(console, 'error')
+      buffer.setText("word")
+      class FailingOperation
+        undo: -> throw new Error("I'm a bad undo operation")
+
+      buffer.insert([0,0], "1")
+      undoManager.pushOperation(new FailingOperation())
+      undoManager.undo()
+      expect(console.error).toHaveBeenCalled()
+      expect(buffer.lineForRow(0)).toBe "1word"
+
+  describe "when an `redo` operation throws an exception", ->
+    it "clears the stack", ->
+      spyOn(console, 'error')
+      buffer.setText("word")
+      class FailingOperation
+        redo: -> throw new Error("I'm a bad undo operation")
+
+      buffer.insert([0,0], "1")
+      undoManager.pushOperation(new FailingOperation())
+      undoManager.undo()
+      undoManager.redo()
+      expect(console.error).toHaveBeenCalled()
+      expect(buffer.lineForRow(0)).toBe "1word"

src/app/undo-manager.coffee

@@ -8,7 +8,10 @@ class UndoManager
   currentTransaction: null
 
   constructor: ->
-    @startBatchCallCount = 0
+    @clear()
+
+  clear: ->
+    @currentTransaction = null
     @undoHistory = []
     @redoHistory = []
 
@@ -18,29 +21,50 @@ class UndoManager
     else
       @undoHistory.push([operation])
     @redoHistory = []
-    operation.do?(editSession)
+
+    try
+      operation.do?(editSession)
+    catch e
+      console.error e.stack
+      @clear()
 
   transact: (fn) ->
+    safeFn = ->
+      try
+        fn()
+      catch e
+        console.error e.stack
+
     if @currentTransaction
-      fn()
+      safeFn()
     else
       @currentTransaction = []
-      fn()
-      @undoHistory.push(@currentTransaction) if @currentTransaction.length
+      safeFn()
+      @undoHistory.push(@currentTransaction) if @currentTransaction?.length
       @currentTransaction = null
 
   undo: (editSession) ->
-    if batch = @undoHistory.pop()
-      opsInReverse = new Array(batch...)
-      opsInReverse.reverse()
-      op.undo?(editSession) for op in opsInReverse
-      @redoHistory.push batch
-      batch.oldSelectionRanges
+    try
+      if batch = @undoHistory.pop()
+        opsInReverse = new Array(batch...)
+        opsInReverse.reverse()
+        op.undo?(editSession) for op in opsInReverse
+
+        @redoHistory.push batch
+        batch.oldSelectionRanges
+    catch e
+      console.error e.stack
+      @clear()
 
   redo: (editSession) ->
-    if batch = @redoHistory.pop()
-      for op in batch
-        op.do?(editSession)
-        op.redo?(editSession)
-      @undoHistory.push(batch)
-      batch.newSelectionRanges
+    try
+      if batch = @redoHistory.pop()
+        for op in batch
+          op.do?(editSession)
+          op.redo?(editSession)
+
+        @undoHistory.push(batch)
+        batch.newSelectionRanges
+    catch e
+      console.error e.stack
+      @clear()