WIP: Relax keyword argument matching

When a method doesn't accept keyword arguments.

In this scenario keyword or Hash-type arguments are assigned as a single
Hash to the last argument without any warnings and strict keyword
matching should not have any effect.

This is an exploratory spike on fixing #593.

* This has highlighted a significant problem with partial mocks in #532.
  The method obtained from the responder is the stub method defined by
  Mocha and not the original. This effectively makes it useless!

* I'm not sure the method_accepts_keyword_arguments? belongs on
  Invocation, but that's the most convenient place for now. It feels as
  if we need to have a bit of a sort out of where various things live
  and perhaps introduce some new classes to make things clearer.

* We might want to think ahead a bit at what we want to do in #149 to
  decide the best way to go about this.

* I'm not sure it's sensible to re-use the Equals matcher; we could
  instead parameterize PositionalOrKeywordHash, although the logic in
  there is already quite complex. Conversely if this is a good approach,
  it might make more sense to do something similar when creating a hash
  matcher for a non-last parameter to further simplify the code.

* I haven't yet introduced any acceptance tests for this and I suspect
  there might be some edge cases yet to come out of the woodwork. In
  particular, I think it's worth exhaustively working through the
  various references mentioned in this comment [1].

[1]: #593 (comment)

lib/mocha/expectation.rb

@@ -639,7 +639,7 @@ def matches_method?(method_name)
 
     # @private
     def match?(invocation)
-      @method_matcher.match?(invocation.method_name) && @parameters_matcher.match?(invocation.arguments) && @block_matcher.match?(invocation.block) && in_correct_order?
+      @method_matcher.match?(invocation.method_name) && @parameters_matcher.match?(invocation) && @block_matcher.match?(invocation.block) && in_correct_order?
     end
 
     # @private

lib/mocha/invocation.rb

@@ -8,11 +8,12 @@ module Mocha
   class Invocation
     attr_reader :method_name, :block
 
-    def initialize(mock, method_name, arguments = [], block = nil)
+    def initialize(mock, method_name, arguments = [], block = nil, responder = nil)
       @mock = mock
       @method_name = method_name
       @arguments = arguments
       @block = block
+      @responder = responder
       @yields = []
       @result = nil
     end
@@ -62,6 +63,12 @@ def full_description
       "\n  - #{call_description} #{result_description}"
     end
 
+    def method_accepts_keyword_arguments?
+      return true unless @responder
+
+      @responder.method(@method_name).parameters.any? { |k, v| %i(keyreq key keyrest).include?(k) }
+    end
+
     private
 
     def argument_description

lib/mocha/mock.rb

@@ -321,7 +321,7 @@ def method_missing(symbol, *arguments, &block)
     def handle_method_call(symbol, arguments, block)
       check_expiry
       check_responder_responds_to(symbol)
-      invocation = Invocation.new(self, symbol, arguments, block)
+      invocation = Invocation.new(self, symbol, arguments, block, @responder)
       if (matching_expectation_allowing_invocation = all_expectations.match_allowing_invocation(invocation))
         matching_expectation_allowing_invocation.invoke(invocation)
       elsif (matching_expectation = all_expectations.match(invocation)) || (!matching_expectation && !@everything_stubbed)

lib/mocha/parameter_matchers/instance_methods.rb

@@ -6,7 +6,7 @@ module ParameterMatchers
     # @private
     module InstanceMethods
       # @private
-      def to_matcher(_expectation = nil)
+      def to_matcher(_expectation = nil, _method_accepts_keyword_arguments = true)
         Mocha::ParameterMatchers::Equals.new(self)
       end
     end
@@ -21,7 +21,11 @@ class Object
 # @private
 class Hash
   # @private
-  def to_matcher(expectation = nil)
-    Mocha::ParameterMatchers::PositionalOrKeywordHash.new(self, expectation)
+  def to_matcher(expectation = nil, method_accepts_keyword_arguments = true)
+    if method_accepts_keyword_arguments
+      Mocha::ParameterMatchers::PositionalOrKeywordHash.new(self, expectation)
+    else
+      Mocha::ParameterMatchers::Equals.new(self)
+    end
   end
 end

lib/mocha/parameters_matcher.rb

@@ -9,26 +9,23 @@ def initialize(expected_parameters = [ParameterMatchers::AnyParameters.new], exp
       @matching_block = matching_block
     end
 
-    def match?(actual_parameters = [])
+    def match?(invocation)
+      actual_parameters = invocation.arguments || []
       if @matching_block
         @matching_block.call(*actual_parameters)
       else
-        parameters_match?(actual_parameters)
+        matchers(invocation).all? { |matcher| matcher.matches?(actual_parameters) } && actual_parameters.empty?
       end
     end
 
-    def parameters_match?(actual_parameters)
-      matchers.all? { |matcher| matcher.matches?(actual_parameters) } && actual_parameters.empty?
-    end
-
     def mocha_inspect
       signature = matchers.mocha_inspect
       signature = signature.gsub(/^\[|\]$/, '')
       "(#{signature})"
     end
 
-    def matchers
-      @expected_parameters.map { |p| p.to_matcher(@expectation) }
+    def matchers(invocation)
+      @expected_parameters.map { |p| p.to_matcher(@expectation, invocation.method_accepts_keyword_arguments?) }
     end
   end
 end