Honor item specificity while still preserving addition order

Rather than using order to specify item precedence, we now construct
a set of menu items for each element traversing upward from the target.
When merging items for a given element, we pass the specificity to the
merge function, which uses it to decide whether or not to clobber
existing items. When assembling the overall menu, we don’t ever clobber
to ensure that items added for elements closer to the target always win
over items matching further up the tree.

spec/context-menu-manager-spec.coffee

@@ -68,6 +68,8 @@ describe "ContextMenuManager", ->
         '.grandchild.foo': [{label: 'A', command: 'b'}]
       disposable3 = contextMenu.add
         '.grandchild': [{label: 'A', command: 'c'}]
+      disposable4 = contextMenu.add
+        '.child': [{label: 'A', command: 'd'}]
 
       expect(contextMenu.templateForElement(grandchild)).toEqual [{label: 'A', command: 'b'}]
 
@@ -77,6 +79,9 @@ describe "ContextMenuManager", ->
       disposable3.dispose()
       expect(contextMenu.templateForElement(grandchild)).toEqual [{label: 'A', command: 'a'}]
 
+      disposable1.dispose()
+      expect(contextMenu.templateForElement(grandchild)).toEqual [{label: 'A', command: 'd'}]
+
     it "allows multiple separators", ->
       contextMenu.add
         '.grandchild': [

src/context-menu-manager.coffee

@@ -10,7 +10,6 @@ Grim = require 'grim'
 MenuHelpers = require './menu-helpers'
 
 SpecificityCache = {}
-SequenceCount = 0
 
 # Extended: Provides a registry for commands that you'd like to appear in the
 # context menu.
@@ -91,7 +90,7 @@ class ContextMenuManager
     addedItemSets = []
 
     for selector, items of itemsBySelector
-      itemSet = new ContextMenuItemSet(selector, items.slice())
+      itemSet = new ContextMenuItemSet(selector, items)
       addedItemSets.push(itemSet)
       @itemSets.push(itemSet)
 
@@ -107,19 +106,21 @@ class ContextMenuManager
     currentTarget = event.target
 
     while currentTarget?
+      currentTargetItems = []
       matchingItemSets =
-        @itemSets
-          .filter (itemSet) -> currentTarget.webkitMatchesSelector(itemSet.selector)
-          .sort (a, b) -> a.compare(b)
+        @itemSets.filter (itemSet) -> currentTarget.webkitMatchesSelector(itemSet.selector)
 
-      for {items} in matchingItemSets
-        for item in items
+      for itemSet in matchingItemSets
+        for item in itemSet.items
           continue if item.devMode and not @devMode
           item = Object.create(item)
           if typeof item.shouldDisplay is 'function'
             continue unless item.shouldDisplay(event)
           item.created?(event)
-          MenuHelpers.merge(template, MenuHelpers.cloneMenuItem(item))
+          MenuHelpers.merge(currentTargetItems, MenuHelpers.cloneMenuItem(item), itemSet.specificity)
+
+      for item in currentTargetItems
+        MenuHelpers.merge(template, item, false)
 
       currentTarget = currentTarget.parentElement
 
@@ -167,9 +168,3 @@ class ContextMenuManager
 class ContextMenuItemSet
   constructor: (@selector, @items) ->
     @specificity = (SpecificityCache[@selector] ?= specificity(@selector))
-    @sequenceNumber = SequenceCount++
-
-  # more specific / recent item sets sort later, because we clobber existing menu items
-  compare: (other) ->
-    @specificity - other.specificity or
-      @sequenceNumber - other.sequenceNumber

src/menu-helpers.coffee

@@ -1,14 +1,18 @@
 _ = require 'underscore-plus'
 
-merge = (menu, item) ->
+ItemSpecificities = new WeakMap
+
+merge = (menu, item, itemSpecificity=Infinity) ->
+  ItemSpecificities.set(item, itemSpecificity) if itemSpecificity
   matchingItemIndex = findMatchingItemIndex(menu, item)
   matchingItem = menu[matchingItemIndex] unless matchingItemIndex is - 1
 
   if matchingItem?
     if item.submenu?
-      merge(matchingItem.submenu, submenuItem) for submenuItem in item.submenu
-    else
-      menu[matchingItemIndex] = item
+      merge(matchingItem.submenu, submenuItem, itemSpecificity) for submenuItem in item.submenu
+    else if itemSpecificity
+      unless itemSpecificity < ItemSpecificities.get(matchingItem)
+        menu[matchingItemIndex] = item
   else
     menu.push(item)