Add Project@registerOpener(fn) to register custom openers on project

Now packages can register custom handlers for different kinds of file
paths. If the function you register returns a resource for the given
path, it will be returned from Project.open instead of an EditSession.

spec/app/project-spec.coffee

@@ -32,7 +32,7 @@ describe "Project", ->
       fsUtils.remove('/tmp/atom-test-save-sets-project-path')
 
   describe ".open(path)", ->
-    [absolutePath, newBufferHandler, newEditSessionHandler] = []
+    [fooOpener, barOpener, absolutePath, newBufferHandler, newEditSessionHandler] = []
     beforeEach ->
       absolutePath = fsUtils.resolveOnLoadPath('fixtures/dir/a')
       newBufferHandler = jasmine.createSpy('newBufferHandler')
@@ -40,35 +40,50 @@ describe "Project", ->
       newEditSessionHandler = jasmine.createSpy('newEditSessionHandler')
       project.on 'edit-session-created', newEditSessionHandler
 
-    describe "when given an absolute path that hasn't been opened previously", ->
-      it "returns a new edit session for the given path and emits 'buffer-created' and 'edit-session-created' events", ->
-        editSession = project.open(absolutePath)
-        expect(editSession.buffer.getPath()).toBe absolutePath
-        expect(newBufferHandler).toHaveBeenCalledWith editSession.buffer
-        expect(newEditSessionHandler).toHaveBeenCalledWith editSession
+      fooOpener = (path, options) -> { foo: path, options } if path?.match(/\.foo/)
+      barOpener = (path) -> { bar: path } if path?.match(/^bar:\/\//)
+      Project.registerOpener(fooOpener)
+      Project.registerOpener(barOpener)
 
-    describe "when given a relative path that hasn't been opened previously", ->
-      it "returns a new edit session for the given path (relative to the project root) and emits 'buffer-created' and 'edit-session-created' events", ->
-        editSession = project.open('a')
-        expect(editSession.buffer.getPath()).toBe absolutePath
-        expect(newBufferHandler).toHaveBeenCalledWith editSession.buffer
-        expect(newEditSessionHandler).toHaveBeenCalledWith editSession
+    afterEach ->
+      Project.unregisterOpener(fooOpener)
+      Project.unregisterOpener(barOpener)
 
-    describe "when passed the path to a buffer that has already been opened", ->
-      it "returns a new edit session containing previously opened buffer and emits a 'edit-session-created' event", ->
-        editSession = project.open(absolutePath)
-        newBufferHandler.reset()
-        expect(project.open(absolutePath).buffer).toBe editSession.buffer
-        expect(project.open('a').buffer).toBe editSession.buffer
-        expect(newBufferHandler).not.toHaveBeenCalled()
-        expect(newEditSessionHandler).toHaveBeenCalledWith editSession
+    describe "when passed a path that doesn't match a custom opener", ->
+      describe "when given an absolute path that hasn't been opened previously", ->
+        it "returns a new edit session for the given path and emits 'buffer-created' and 'edit-session-created' events", ->
+          editSession = project.open(absolutePath)
+          expect(editSession.buffer.getPath()).toBe absolutePath
+          expect(newBufferHandler).toHaveBeenCalledWith editSession.buffer
+          expect(newEditSessionHandler).toHaveBeenCalledWith editSession
 
-    describe "when not passed a path", ->
-      it "returns a new edit session and emits 'buffer-created' and 'edit-session-created' events", ->
-        editSession = project.open()
-        expect(editSession.buffer.getPath()).toBeUndefined()
-        expect(newBufferHandler).toHaveBeenCalledWith(editSession.buffer)
-        expect(newEditSessionHandler).toHaveBeenCalledWith editSession
+      describe "when given a relative path that hasn't been opened previously", ->
+        it "returns a new edit session for the given path (relative to the project root) and emits 'buffer-created' and 'edit-session-created' events", ->
+          editSession = project.open('a')
+          expect(editSession.buffer.getPath()).toBe absolutePath
+          expect(newBufferHandler).toHaveBeenCalledWith editSession.buffer
+          expect(newEditSessionHandler).toHaveBeenCalledWith editSession
+
+      describe "when passed the path to a buffer that has already been opened", ->
+        it "returns a new edit session containing previously opened buffer and emits a 'edit-session-created' event", ->
+          editSession = project.open(absolutePath)
+          newBufferHandler.reset()
+          expect(project.open(absolutePath).buffer).toBe editSession.buffer
+          expect(project.open('a').buffer).toBe editSession.buffer
+          expect(newBufferHandler).not.toHaveBeenCalled()
+          expect(newEditSessionHandler).toHaveBeenCalledWith editSession
+
+      describe "when not passed a path", ->
+        it "returns a new edit session and emits 'buffer-created' and 'edit-session-created' events", ->
+          editSession = project.open()
+          expect(editSession.buffer.getPath()).toBeUndefined()
+          expect(newBufferHandler).toHaveBeenCalledWith(editSession.buffer)
+          expect(newEditSessionHandler).toHaveBeenCalledWith editSession
+
+    describe "when passed a path that matches a custom opener", ->
+      it "returns the resource returned by the custom opener", ->
+        expect(project.open("a.foo", hey: "there")).toEqual { foo: "a.foo", options: {hey: "there"} }
+        expect(project.open("bar://baz")).toEqual { bar: "bar://baz" }
 
   describe ".bufferForPath(path)", ->
     describe "when opening a previously opened path", ->

src/app/project.coffee

@@ -17,6 +17,14 @@ module.exports =
 class Project
   registerDeserializer(this)
 
+  @openers: []
+
+  @registerOpener: (opener) ->
+    @openers.push(opener)
+
+  @unregisterOpener: (opener) ->
+    _.remove(@openers, opener)
+
   tabLength: 2
   softTabs: true
   softWrap: false
@@ -148,11 +156,14 @@ class Project
   # editSessionOptions - Options that you can pass to the `EditSession` constructor
   #
   # Returns either an {EditSession} (for text) or {ImageEditSession} (for images).
-  open: (filePath, editSessionOptions={}) ->
+  open: (filePath, options={}) ->
+    for opener in @constructor.openers
+      return resource if resource = opener(filePath, options)
+
     if ImageEditSession.canOpen(filePath)
       new ImageEditSession(filePath)
     else
-      @buildEditSessionForBuffer(@bufferForPath(filePath), editSessionOptions)
+      @buildEditSessionForBuffer(@bufferForPath(filePath), options)
 
   # Retrieves all the {EditSession}s in the project; that is, the `EditSession`s for all open files.
   #