Add DisplayBufferMarker::onDidChange and ::onDidDestroy

spec/display-buffer-spec.coffee

@@ -722,7 +722,7 @@ describe "DisplayBuffer", ->
 
       beforeEach ->
         marker = displayBuffer.markScreenRange([[5, 4], [5, 10]])
-        marker.on 'changed', markerChangedHandler = jasmine.createSpy("markerChangedHandler")
+        marker.onDidChange markerChangedHandler = jasmine.createSpy("markerChangedHandler")
 
       it "triggers the 'changed' event whenever the markers head's screen position changes in the buffer or on screen", ->
         marker.setHeadScreenPosition([8, 20])
@@ -859,7 +859,7 @@ describe "DisplayBuffer", ->
 
       it "updates markers before emitting buffer change events, but does not notify their observers until the change event", ->
         marker2 = displayBuffer.markBufferRange([[8, 1], [8, 1]])
-        marker2.on 'changed', marker2ChangedHandler = jasmine.createSpy("marker2ChangedHandler")
+        marker2.onDidChange marker2ChangedHandler = jasmine.createSpy("marker2ChangedHandler")
         displayBuffer.on 'changed', changeHandler = jasmine.createSpy("changeHandler").andCallFake -> onDisplayBufferChange()
 
         # New change ----
@@ -886,7 +886,7 @@ describe "DisplayBuffer", ->
         marker2ChangedHandler.reset()
 
         marker3 = displayBuffer.markBufferRange([[8, 1], [8, 2]])
-        marker3.on 'changed', marker3ChangedHandler = jasmine.createSpy("marker3ChangedHandler")
+        marker3.onDidChange marker3ChangedHandler = jasmine.createSpy("marker3ChangedHandler")
 
         onDisplayBufferChange = ->
           # calls change handler first

src/cursor.coffee

@@ -44,7 +44,7 @@ class Cursor extends Model
   constructor: ({@editor, @marker, id}) ->
     @assignId(id)
     @updateVisibility()
-    @marker.on 'changed', (e) =>
+    @marker.onDidChange (e) =>
       @updateVisibility()
       {oldHeadScreenPosition, newHeadScreenPosition} = e
       {oldHeadBufferPosition, newHeadBufferPosition} = e
@@ -66,7 +66,7 @@ class Cursor extends Model
 
       @emit 'moved', movedEvent
       @editor.cursorMoved(this, movedEvent)
-    @marker.on 'destroyed', =>
+    @marker.onDidDestroy =>
       @destroyed = true
       @editor.removeCursor(this)
       @emit 'destroyed'

src/display-buffer-marker.coffee

@@ -1,10 +1,12 @@
 {Range} = require 'text-buffer'
 _ = require 'underscore-plus'
-{Emitter, Subscriber} = require 'emissary'
+{Subscriber} = require 'emissary'
+EmitterMixin = require('emissary').Emitter
+{Emitter} = require 'event-kit'
 
 module.exports =
 class DisplayBufferMarker
-  Emitter.includeInto(this)
+  EmitterMixin.includeInto(this)
   Subscriber.includeInto(this)
 
   bufferMarkerSubscription: null
@@ -15,6 +17,7 @@ class DisplayBufferMarker
   wasValid: true
 
   constructor: ({@bufferMarker, @displayBuffer}) ->
+    @emitter = new Emitter
     @id = @bufferMarker.id
     @oldHeadBufferPosition = @getHeadBufferPosition()
     @oldHeadScreenPosition = @getHeadScreenPosition()
@@ -25,6 +28,12 @@ class DisplayBufferMarker
     @subscribe @bufferMarker.onDidDestroy => @destroyed()
     @subscribe @bufferMarker.onDidChange (event) => @notifyObservers(event)
 
+  onDidChange: (callback) ->
+    @emitter.on 'did-change', callback
+
+  onDidDestroy: (callback) ->
+    @emitter.on 'did-destroy', callback
+
   copy: (attributes) ->
     @displayBuffer.getMarker(@bufferMarker.copy(attributes).id)
 
@@ -199,6 +208,8 @@ class DisplayBufferMarker
   destroyed: ->
     delete @displayBuffer.markers[@id]
     @emit 'destroyed'
+    @emitter.emit 'did-destroy'
+    @emitter.dispose()
 
   notifyObservers: ({textChanged}) ->
     textChanged ?= false
@@ -215,7 +226,7 @@ class DisplayBufferMarker
       _.isEqual(newTailBufferPosition, @oldTailBufferPosition) and
       _.isEqual(newTailScreenPosition, @oldTailScreenPosition)
 
-    @emit 'changed', {
+    changeEvent = {
       @oldHeadScreenPosition, newHeadScreenPosition,
       @oldTailScreenPosition, newTailScreenPosition,
       @oldHeadBufferPosition, newHeadBufferPosition,
@@ -223,6 +234,8 @@ class DisplayBufferMarker
       textChanged,
       isValid
     }
+    @emit 'changed', changeEvent
+    @emitter.emit 'did-change', changeEvent
 
     @oldHeadBufferPosition = newHeadBufferPosition
     @oldHeadScreenPosition = newHeadScreenPosition

src/selection.coffee

@@ -30,8 +30,8 @@ class Selection extends Model
     @cursor.selection = this
     @decoration = @editor.decorateMarker(@marker, type: 'highlight', class: 'selection')
 
-    @marker.on 'changed', => @screenRangeChanged()
+    @marker.onDidChange => @screenRangeChanged()
-    @marker.on 'destroyed', =>
+    @marker.onDidDestroy =>
       @destroyed = true
       @editor.removeSelection(this)
       @emit 'destroyed' unless @editor.isDestroyed()