[bugfix] Properly detect kwargs hashes vs optional positional args

lib/rspec/support/method_signature_verifier.rb

@@ -79,12 +79,35 @@ def invalid_kw_args_from(given_kw_args)
           given_kw_args - @allowed_kw_args
         end
 
-        # If the last argument is Hash, Ruby will treat only symbol keys as keyword arguments
-        # the rest will be grouped in another Hash and passed as positional argument.
+        # Considering the arg types, are there kw_args?
         def has_kw_args_in?(args)
-          Hash === args.last &&
-            could_contain_kw_args?(args) &&
-            (RubyFeatures.kw_arg_separation? || args.last.empty? || args.last.keys.any? { |x| x.is_a?(Symbol) })
+          if RubyFeatures.kw_arg_separation?
+            # If the last arg is a hash, depending on the signature it could be kw_args or a positional parameter.
+            return false unless Hash === args.last && could_contain_kw_args?(args)
+
+            # If the position of the hash is beyond the count of required and optional positional
+            # args then it is the kwargs hash
+            return true if args.count > @max_non_kw_args
+
+            # This is the proper way to disambiguate between positional args and keywords hash
+            # but relies on beginning of the call chain annotating the method with
+            # ruby2_keywords, so only use it for positive feedback as without the annotation
+            # this is always false
+            return true if Hash.ruby2_keywords_hash?(args[-1])
+
+            # Otherwise, the hash could be defined kw_args or an optional positional parameter
+            # inspect the keys against known kwargs to determine what it is
+            # Note: the problem with this is that if a user passes only invalid keyword args,
+            #       rspec no longer detects is and will assign this to a positional argument
+            return arbitrary_kw_args? || args.last.keys.all? { |x| @allowed_kw_args.include?(x) }
+          else
+            # Version <= Ruby 2.7
+            # If the last argument is Hash, Ruby will treat only symbol keys as keyword arguments
+            # the rest will be grouped in another Hash and passed as positional argument.
+            Hash === args.last &&
+              could_contain_kw_args?(args) &&
+              (args.last.empty? || args.last.keys.any? { |x| x.is_a?(Symbol) })
+          end
         end
 
         # Without considering what the last arg is, could it

spec/rspec/support/method_signature_verifier_spec.rb

@@ -10,15 +10,15 @@ def valid_non_kw_args?(arity)
         described_class.new(signature, [nil] * arity).valid?
       end
 
-      def valid?(*args)
+      ruby2_keywords def valid?(*args)
         described_class.new(signature, args).valid?
       end
 
       def error_description
         described_class.new(signature).error_message[/Expected (.*),/, 1]
       end
 
-      def error_for(*args)
+      ruby2_keywords def error_for(*args)
         described_class.new(signature, args).error_message
       end