Add Workspace::onWillDestroyPaneItem

It is needed by the autosave package which previously relied on DOM
bubbling to coalesce events from various panes.

spec/pane-container-spec.coffee

@@ -148,3 +148,30 @@ describe "PaneContainer", ->
       saved = container.confirmClose()
       expect(saved).toBeFalsy()
       expect(atom.confirm).toHaveBeenCalled()
+
+  describe "::onWillDestroyPaneItem() and ::onDidDestroyPaneItem", ->
+    it "invokes the given callbacks when an item will be destroyed on any pane", ->
+      container = new PaneContainer
+      pane1 = container.getRoot()
+      item1 = new Object
+      item2 = new Object
+      item3 = new Object
+
+      pane1.addItem(item1)
+      events = []
+      container.onWillDestroyPaneItem (event) -> events.push(['will', event])
+      container.onDidDestroyPaneItem (event) -> events.push(['did', event])
+      pane2 = pane1.splitRight(items: [item2, item3])
+
+      pane1.destroyItem(item1)
+      pane2.destroyItem(item3)
+      pane2.destroyItem(item2)
+
+      expect(events).toEqual [
+        ['will', {item: item1, pane: pane1, index: 0}]
+        ['did', {item: item1, pane: pane1, index: 0}]
+        ['will', {item: item3, pane: pane2, index: 1}]
+        ['did', {item: item3, pane: pane2, index: 1}]
+        ['will', {item: item2, pane: pane2, index: 0}]
+        ['did', {item: item2, pane: pane2, index: 0}]
+      ]

src/pane-container.coffee

@@ -112,6 +112,9 @@ class PaneContainer extends Model
     fn(@getActivePaneItem())
     @onDidChangeActivePaneItem(fn)
 
+  onWillDestroyPaneItem: (fn) ->
+    @emitter.on 'will-destroy-pane-item', fn
+
   onDidDestroyPaneItem: (fn) ->
     @emitter.on 'did-destroy-pane-item', fn
 
@@ -193,8 +196,11 @@ class PaneContainer extends Model
   destroyEmptyPanes: ->
     pane.destroy() for pane in @getPanes() when pane.items.length is 0
 
-  paneItemDestroyed: (item) ->
-    @emitter.emit 'did-destroy-pane-item', item
+  willDestroyPaneItem: (event) ->
+    @emitter.emit 'will-destroy-pane-item', event
+
+  didDestroyPaneItem: (event) ->
+    @emitter.emit 'did-destroy-pane-item', event
 
   didAddPane: (pane) ->
     @emitter.emit 'did-add-pane', pane

src/pane.coffee

@@ -371,7 +371,7 @@ class Pane extends Model
     @items.splice(index, 1)
     @emit 'item-removed', item, index, destroyed
     @emitter.emit 'did-remove-item', {item, index, destroyed}
-    @container?.paneItemDestroyed(item) if destroyed
+    @container?.didDestroyPaneItem({item, index, pane: this}) if destroyed
     @destroy() if @items.length is 0 and atom.config.get('core.destroyEmptyPanes')
 
   # Public: Move the given item to the given index.
@@ -410,6 +410,7 @@ class Pane extends Model
     if index isnt -1
       @emit 'before-item-destroyed', item
       @emitter.emit 'will-destroy-item', {item, index}
+      @container?.willDestroyPaneItem({item, index, pane: this})
       if @promptToSaveItem(item)
         @removeItem(item, true)
         item.destroy?()

src/workspace.coffee

@@ -47,7 +47,7 @@ class Workspace extends Model
 
     viewRegistry = atom.views
     @paneContainer ?= new PaneContainer({viewRegistry})
-    @paneContainer.onDidDestroyPaneItem(@onPaneItemDestroyed)
+    @paneContainer.onDidDestroyPaneItem(@didDestroyPaneItem)
 
     @panelContainers =
       top: new PanelContainer({viewRegistry, location: 'top'})
@@ -271,7 +271,7 @@ class Workspace extends Model
   # Extended: Invoke the given callback when a pane item is added to the
   # workspace.
   #
-  # * `callback` {Function} to be called when panes are added.
+  # * `callback` {Function} to be called when pane items are added.
   #   * `event` {Object} with the following keys:
   #     * `item` The added pane item.
   #     * `pane` {Pane} containing the added item.
@@ -280,6 +280,19 @@ class Workspace extends Model
   # Returns a {Disposable} on which `.dispose()` can be called to unsubscribe.
   onDidAddPaneItem: (callback) -> @paneContainer.onDidAddPaneItem(callback)
 
+  # Extended: Invoke the given callback when a pane item is about to be
+  # destroyed, before the user is prompted to save it.
+  #
+  # * `callback` {Function} to be called before pane items are destroyed.
+  #   * `event` {Object} with the following keys:
+  #     * `item` The item to be destroyed.
+  #     * `pane` {Pane} containing the item to be destroyed.
+  #     * `index` {Number} indicating the index of the item to be destroyed in
+  #       its pane.
+  #
+  # Returns a {Disposable} on which `.dispose` can be called to unsubscribe.
+  onWillDestroyPaneItem: (callback) -> @paneContainer.onWillDestroyPaneItem(callback)
+
   # Extended: Invoke the given callback when a text editor is added to the
   # workspace.
   #
@@ -605,7 +618,7 @@ class Workspace extends Model
       _.remove(@destroyedItemUris, uri)
 
   # Adds the destroyed item's uri to the list of items to reopen.
-  onPaneItemDestroyed: (item) =>
+  didDestroyPaneItem: ({item}) =>
     if uri = item.getUri?()
       @destroyedItemUris.push(uri)