Extract Rails extension to have matcher

Gemfile

@@ -12,13 +12,16 @@ gemspec
   end
 end
 
-# only the master branche is supported on rspec-support
+# only the master branch is supported on rspec-support
 gem "rspec-support", :git => "git://github.com/rspec/rspec-support.git"
 
 gem "cucumber", "~> 1.1.9"
 gem "aruba",    "~> 0.5"
 gem "rake",     "~> 10.0.0"
 
+# for optional rails support
+gem 'activesupport', RUBY_VERSION < "1.9.3" ? '~> 3.0' : '>= 3.0'
+
 platform :rbx do
   gem 'rubysl'
 end

lib/rspec/collection_matchers.rb

@@ -1,3 +1,9 @@
 require 'rspec/collection_matchers/version'
 require 'rspec/collection_matchers/matchers'
 require 'rspec/collection_matchers/have'
+
+begin
+  require 'rspec/collection_matchers/rails/have_extensions'
+rescue LoadError
+  # must not have rails
+end

lib/rspec/collection_matchers/rails/have_extensions.rb

@@ -0,0 +1,56 @@
+require 'active_support/concern'
+require 'active_support/core_ext/module/aliasing'
+
+module RSpec
+  module CollectionMatchers
+    module Rails
+      module HaveExtensions
+        extend ActiveSupport::Concern
+
+        # @api private
+        #
+        # Enhances the failure message for `to have(n)` matchers
+        def failure_message_with_errors_on_extensions
+          return errors_on_message(:expected, ", got #{@actual}") if is_errors_on?
+          failure_message_without_errors_on_extensions
+        end
+
+        # @api private
+        #
+        # Enhances the description for `to have(n)` matchers
+        def description_with_errors_on_extensions
+          return errors_on_message(:have) if is_errors_on?
+          description_without_errors_on_extensions
+        end
+
+        included do
+          alias_method_chain :failure_message, :errors_on_extensions
+          alias_method_chain :description, :errors_on_extensions
+
+          ## For RSpec 2.99 compatibility
+          rspec_2x_matcher_failure_method = :failure_message_for_should
+          rspec_2x_matcher_failure_method = rspec_2x_matcher_failure_method.to_s if RUBY_VERSION < '1.9'
+          if instance_methods.include? rspec_2x_matcher_failure_method
+            alias failure_message_for_should_with_errors_on_extensions failure_message_with_errors_on_extensions
+            alias_method_chain :failure_message_for_should, :errors_on_extensions
+            alias failure_message_without_errors_on_extensions failure_message_for_should_without_errors_on_extensions
+          end
+        end
+
+        # @api private
+        def is_errors_on?
+          [:errors_on, :error_on].include? @collection_name
+        end
+
+        # @api private
+        def errors_on_message(prefix, suffix = nil)
+          "#{prefix} #{relative_expectation} #{@collection_name.to_s.gsub('_', ' ')} :#{@args[0]}#{suffix}"
+        end
+      end
+    end
+  end
+end
+
+RSpec::CollectionMatchers::Have.class_eval do
+  include RSpec::CollectionMatchers::Rails::HaveExtensions
+end

spec/rspec/collection_matchers/rails/have_extensions_spec.rb

@@ -0,0 +1,42 @@
+require "spec_helper"
+require 'rspec/collection_matchers/rails/have_extensions'
+
+module RSpec::CollectionMatchers::Rails
+  describe HaveExtensions do
+    describe "error_on" do
+      it "provides a description including the name of what the error is on" do
+        expect(have(1).error_on(:whatever).description).to eq "have 1 error on :whatever"
+      end
+
+      it "provides a failure message including the number actually given" do
+        expect {
+          [].should have(1).error_on(:whatever)
+        }.to raise_error("expected 1 error on :whatever, got 0")
+      end
+    end
+
+    describe "errors_on" do
+      it "provides a description including the name of what the error is on" do
+        expect(have(2).errors_on(:whatever).description).to eq "have 2 errors on :whatever"
+      end
+
+      it "provides a failure message including the number actually given" do
+        expect {
+          [1].should have(3).errors_on(:whatever)
+        }.to raise_error("expected 3 errors on :whatever, got 1")
+      end
+    end
+
+    describe "have something other than error_on or errors_on" do
+      it "has a standard rspec failure message" do
+        expect {
+          [1,2,3].should have(2).elements
+        }.to raise_error("expected 2 elements, got 3")
+      end
+
+      it "has a standard rspec description" do
+        expect(have(2).elements.description).to eq "have 2 elements"
+      end
+    end
+  end
+end