Notify observers when markers are invalidated/revalidated

spec/app/buffer-spec.coffee

@@ -741,6 +741,7 @@ describe 'Buffer', ->
           oldTailPosition: [4, 20]
           newTailPosition: [4, 20]
           bufferChanged: false
+          valid: true
         }
         observeHandler.reset()
 
@@ -751,6 +752,7 @@ describe 'Buffer', ->
           oldHeadPosition: [6, 2]
           newHeadPosition: [6, 5]
           bufferChanged: true
+          valid: true
         }
 
       it "calls the given callback when the marker's tail position changes", ->
@@ -762,6 +764,7 @@ describe 'Buffer', ->
           oldTailPosition: [4, 20]
           newTailPosition: [6, 2]
           bufferChanged: false
+          valid: true
         }
         observeHandler.reset()
 
@@ -773,6 +776,7 @@ describe 'Buffer', ->
           oldTailPosition: [6, 2]
           newTailPosition: [6, 5]
           bufferChanged: true
+          valid: true
         }
 
       it "calls the callback when the selection's tail is cleared", ->
@@ -784,6 +788,7 @@ describe 'Buffer', ->
           oldTailPosition: [4, 20]
           newTailPosition: [4, 23]
           bufferChanged: false
+          valid: true
         }
 
       it "only calls the callback once when both the marker's head and tail positions change due to the same operation", ->
@@ -795,6 +800,7 @@ describe 'Buffer', ->
           oldHeadPosition: [4, 23]
           newHeadPosition: [4, 26]
           bufferChanged: true
+          valid: true
         }
         observeHandler.reset()
 
@@ -806,6 +812,31 @@ describe 'Buffer', ->
           oldHeadPosition: [4, 26]
           newHeadPosition: [1, 1]
           bufferChanged: false
+          valid: true
+        }
+
+      it "calls the callback with the valid flag set to false when the marker is invalidated", ->
+        buffer.deleteRow(4)
+        expect(observeHandler.callCount).toBe 1
+        expect(observeHandler.argsForCall[0][0]).toEqual {
+          oldTailPosition: [4, 20]
+          newTailPosition: [4, 20]
+          oldHeadPosition: [4, 23]
+          newHeadPosition: [4, 23]
+          bufferChanged: true
+          valid: false
+        }
+
+        observeHandler.reset()
+        buffer.undo()
+        expect(observeHandler.callCount).toBe 1
+        expect(observeHandler.argsForCall[0][0]).toEqual {
+          oldTailPosition: [4, 20]
+          newTailPosition: [4, 20]
+          oldHeadPosition: [4, 23]
+          newHeadPosition: [4, 23]
+          bufferChanged: true
+          valid: true
         }
 
       it "allows the observation subscription to be cancelled", ->

src/app/buffer-change-operation.coffee

@@ -107,5 +107,4 @@ class BufferChangeOperation
       if validMarker = @buffer.validMarkers[id]
         validMarker.setRange(previousRange)
       else if invalidMarker = @buffer.invalidMarkers[id]
-        @buffer.validMarkers[id] = invalidMarker
-
+        invalidMarker.revalidate()

src/app/buffer-marker.coffee

@@ -113,23 +113,31 @@ class BufferMarker
     [newRow, newColumn]
 
   observe: (callback) ->
-    @on 'position-changed', callback
+    @on 'changed', callback
     cancel: => @unobserve(callback)
 
   unobserve: (callback) ->
-    @off 'position-changed', callback
+    @off 'changed', callback
 
   containsPoint: (point) ->
     @getRange().containsPoint(point)
 
-  notifyObservers: ({oldHeadPosition, newHeadPosition, oldTailPosition, newTailPosition, bufferChanged}) ->
+  notifyObservers: ({oldHeadPosition, newHeadPosition, oldTailPosition, newTailPosition, bufferChanged} = {}) ->
     return if @suppressObserverNotification
-    return if _.isEqual(newHeadPosition, oldHeadPosition) and _.isEqual(newTailPosition, oldTailPosition)
+
+    if newHeadPosition? and newTailPosition?
+      return if _.isEqual(newHeadPosition, oldHeadPosition) and _.isEqual(newTailPosition, oldTailPosition)
+    else if newHeadPosition?
+      return if _.isEqual(newHeadPosition, oldHeadPosition)
+    else if newTailPosition?
+      return if _.isEqual(newTailPosition, oldTailPosition)
+
     oldHeadPosition ?= @getHeadPosition()
     newHeadPosition ?= @getHeadPosition()
     oldTailPosition ?= @getTailPosition()
     newTailPosition ?= @getTailPosition()
-    @trigger 'position-changed', {oldHeadPosition, newHeadPosition, oldTailPosition, newTailPosition, bufferChanged}
+    valid = @buffer.validMarkers[@id]?
+    @trigger 'changed', {oldHeadPosition, newHeadPosition, oldTailPosition, newTailPosition, bufferChanged, valid}
 
   consolidateObserverNotifications: (bufferChanged, fn) ->
     @suppressObserverNotification = true
@@ -144,5 +152,11 @@ class BufferMarker
   invalidate: ->
     delete @buffer.validMarkers[@id]
     @buffer.invalidMarkers[@id] = this
+    @notifyObservers(bufferChanged: true)
+
+  revalidate: ->
+    delete @buffer.invalidMarkers[@id]
+    @buffer.validMarkers[@id] = this
+    @notifyObservers(bufferChanged: true)
 
 _.extend BufferMarker.prototype, EventEmitter