passing a block to #pass will not 404, but eval the block

This is huge for writing extensions that install routes.
The developer can set the block to do default behaviour
if the app that registered the extension has not, or does
not want to, customize the route.

example:

  # MyFooExt
  ...
  def self.registered(app)
    app.get "/foo" do
      do_foo_things
      pass do
        "You hit foo!"
      end
    end
  end

At this point, as the user of MyFooExt, I can let the default
behaviour happen or override:

  # MySinatraApp
  require 'sinatra/my_foo_ext'

  class MySinatraApp < Sinatra::Base
    register MyFooExt

    get "/foo" do
      # MyFooExt has done do_foo_things
      do_our_foo_things
      "All foo things done"
    end
  end

lib/sinatra/base.rb

@@ -416,8 +416,8 @@ module Sinatra
     # Pass control to the next matching route.
     # If there are no more matching routes, Sinatra will
     # return a 404 response.
-    def pass
-      throw :pass
+    def pass(&block)
+      throw :pass, block
     end
 
     # Forward the request to the downstream app -- middleware only.
@@ -444,7 +444,7 @@ module Sinatra
     end
 
     # Run routes defined on the class and all superclasses.
-    def route!(base=self.class)
+    def route!(base=self.class, pass_block=nil)
       if routes = base.routes[@request.request_method]
         original_params = @params
         path            = unescape(@request.path_info)
@@ -470,7 +470,7 @@ module Sinatra
             @params = original_params.merge(params)
             @block_params = values
 
-            catch(:pass) do
+            pass_block = catch(:pass) do
               conditions.each { |cond|
                 throw :pass if instance_eval(&cond) == false }
               route_eval(&block)
@@ -483,10 +483,12 @@ module Sinatra
 
       # Run routes defined in superclass.
       if base.superclass.respond_to?(:routes)
-        route! base.superclass
+        route! base.superclass, pass_block
         return
       end
 
+      route_eval(&pass_block) if pass_block
+
       route_missing
     end
 

test/routing_test.rb

@@ -462,6 +462,21 @@ class RoutingTest < Test::Unit::TestCase
     assert not_found?
   end
 
+  it "uses optional block passed to pass as route block if no other route is found" do
+    mock_app {
+      get "/" do
+        pass do
+          "this"
+        end
+        "not this"
+      end
+    }
+
+    get "/"
+    assert ok?
+    assert "this", body
+  end
+
   it "passes when matching condition returns false" do
     mock_app {
       condition { params[:foo] == 'bar' }