WIP: Destroy nested tab stops when engulfed by a buffer change

Has 2 failing specs...

There are still some issue with this code's interaction with the undo
system. The tab stops will need to be or destroyed when certain
changes are undone or redone.

.atom/snippets/coffee.cson

@@ -35,6 +35,10 @@
   "Point array":
     prefix: "pt"
     body: "[$1, $2]"
+
+  "Key-value pair":
+    prefix: ":"
+    body: '${1:"${2:key}"}: ${3:value}'
   "Create Jasmine spy":
     prefix: "pt"
     body: 'jasmine.createSpy("${1:description}")$2'

src/app/anchor-range.coffee

@@ -1,4 +1,7 @@
 Range = require 'range'
+EventEmitter = require 'event-emitter'
+Subscriber = require 'subscriber'
+_ = require 'underscore'
 
 module.exports =
 class AnchorRange
@@ -6,11 +9,14 @@ class AnchorRange
   end: null
   buffer: null
   editSession: null # optional
+  destroyed: false
 
   constructor: (bufferRange, @buffer, @editSession) ->
     bufferRange = Range.fromObject(bufferRange)
     @startAnchor = @buffer.addAnchorAtPosition(bufferRange.start, ignoreChangesStartingOnAnchor: true)
     @endAnchor = @buffer.addAnchorAtPosition(bufferRange.end)
+    @subscribe @startAnchor, 'destroyed', => @destroy()
+    @subscribe @endAnchor, 'destroyed', => @destroy()
 
   getBufferRange: ->
     new Range(@startAnchor.getBufferPosition(), @endAnchor.getBufferPosition())
@@ -22,7 +28,14 @@ class AnchorRange
     @getBufferRange().containsPoint(bufferPosition)
 
   destroy: ->
+    return if @destroyed
+    @unsubscribe()
     @startAnchor.destroy()
     @endAnchor.destroy()
     @buffer.removeAnchorRange(this)
     @editSession?.removeAnchorRange(this)
+    @destroyed = true
+    @trigger 'destroyed'
+
+_.extend(AnchorRange.prototype, EventEmitter)
+_.extend(AnchorRange.prototype, Subscriber)

src/app/anchor.coffee

@@ -10,6 +10,7 @@ class Anchor
   screenPosition: null
   ignoreChangesStartingOnAnchor: false
   strong: false
+  destroyed: false
 
   constructor: (@buffer, options = {}) ->
     { @editSession, @ignoreChangesStartingOnAnchor, @strong } = options
@@ -81,8 +82,10 @@ class Anchor
     @setScreenPosition(screenPosition, bufferChange: options.bufferChange, clip: false, assignBufferPosition: false, autoscroll: options.autoscroll)
 
   destroy: ->
+    return if @destroyed
     @buffer.removeAnchor(this)
     @editSession?.removeAnchor(this)
+    @destroyed = true
     @trigger 'destroyed'
 
 _.extend(Anchor.prototype, EventEmitter)

src/packages/snippets/spec/snippets-spec.coffee

@@ -52,12 +52,9 @@ describe "Snippets extension", ->
 
             """
 
-          "multi-line placeholders":
+          "nested tab stops":
             prefix: "t5"
-            body: """
-              behold ${1:my multi-
-              line placeholder}. amazing.
-            """
+            body: '${1:"${2:key}"}: ${3:value}'
 
           "caused problems with undo":
             prefix: "t6"
@@ -122,6 +119,17 @@ describe "Snippets extension", ->
             editor.trigger keydownEvent('tab', target: editor[0])
             expect(editor.getSelectedBufferRange()).toEqual [[1, 29], [1, 35]]
 
+        describe "when tab stops are nested", ->
+          it "destroys the inner tab stop if the outer tab stop is modified", ->
+            buffer.setText('')
+            editor.insertText 't5'
+            editor.trigger 'snippets:expand'
+            expect(buffer.lineForRow(0)).toBe '"key": value'
+            expect(editor.getSelectedBufferRange()).toEqual [[0, 0], [0, 5]]
+            editor.insertText("foo")
+            editor.trigger keydownEvent('tab', target: editor[0])
+            expect(editor.getSelectedBufferRange()).toEqual [[0, 5], [0, 10]]
+
         describe "when the cursor is moved beyond the bounds of a tab stop", ->
           it "terminates the snippet", ->
             editor.setCursorScreenPosition([2, 0])
@@ -182,7 +190,7 @@ describe "Snippets extension", ->
         editor.trigger keydownEvent('tab', target: editor[0])
         expect(buffer.lineForRow(0)).toBe "first line"
 
-    describe "when a snippet expansion is undone and redone", ->
+    ffdescribe "when a snippet expansion is undone and redone", ->
       it "recreates the snippet's tab stops", ->
         editor.insertText '    t6\n'
         editor.setCursorBufferPosition [0, 6]

src/packages/snippets/src/snippet-expansion.coffee

@@ -25,7 +25,9 @@ class SnippetExpansion
 
   placeTabStopAnchorRanges: (startPosition, tabStopRanges) ->
     @tabStopAnchorRanges = tabStopRanges.map ({start, end}) =>
-      @editSession.addAnchorRange([startPosition.add(start), startPosition.add(end)])
+      anchorRange = @editSession.addAnchorRange([startPosition.add(start), startPosition.add(end)])
+      anchorRange.on 'destroyed', => _.remove(@tabStopAnchorRanges, anchorRange)
+      anchorRange
     @setTabStopIndex(0)
 
   indentSubsequentLines: (startRow, snippet) ->
@@ -68,7 +70,7 @@ class SnippetExpansion
     _.intersection(@tabStopAnchorRanges, @editSession.anchorRangesForBufferPosition(bufferPosition))
 
   destroy: ->
-    anchorRange.destroy() for anchorRange in @tabStopAnchorRanges
+    anchorRange.destroy() for anchorRange in new Array(@tabStopAnchorRanges...)
     @editSession.off '.snippet-expansion'
     @editSession.snippetExpansion = null