Add support for default app (404).remove-execution-variables

2 files changed, 7 insertions, 6 deletions

diff --git a/lib/rack/builder.rb b/lib/rack/builder.rb
index 6f2ab0aa..fa64ae3e 100644
--- a/lib/rack/builder.rb
+++ b/lib/rack/builder.rb
@@ -109,10 +109,12 @@ module Rack
       return builder.to_app
     end
 
+    DEFAULT_APP = proc{|env| [404, [], []]}
+
     # Initialize a new Rack::Builder instance.  +default_app+ specifies the
     # default application if +run+ is not called later.  If a block
     # is given, it is evaluted in the context of the instance.
-    def initialize(default_app = nil, **options, &block)
+    def initialize(default_app = DEFAULT_APP, **options, &block)
       @use = []
       @map = nil
       @run = default_app
@@ -247,8 +249,8 @@ module Rack
     # Return the Rack application generated by this instance.
     def to_app
       app = @map ? generate_map(@run, @map) : @run
-      fail "missing run or map statement" unless app
       app.freeze if @freeze_app
+
       app = @use.reverse.inject(app) { |a, e| e[a].tap { |x| x.freeze if @freeze_app } }
       @warmup.call(app) if @warmup
       app
diff --git a/test/spec_builder.rb b/test/spec_builder.rb
index eb13a976..3fcc9933 100644
--- a/test/spec_builder.rb
+++ b/test/spec_builder.rb
@@ -218,10 +218,9 @@ describe Rack::Builder do
     Rack::MockRequest.new(app).get("/c").status.must_equal 200
   end
 
-  it 'complains about a missing run' do
-    proc do
-      Rack::Lint.new Rack::Builder.app { use Rack::ShowExceptions }
-    end.must_raise(RuntimeError)
+  it 'should result in the default app' do
+    app = Rack::Builder.new.to_app
+    app.must_equal Rack::Builder::DEFAULT_APP
   end
 
   describe "parse_file" do