Make usage of keyword arguments for String#encode explicit to avoid warning on 2.7.0

Author: JonRowe

lib/rspec/support/encoded_string.rb

@@ -112,11 +112,40 @@ def matching_encoding(string)
           string = remove_invalid_bytes(string)
           string.encode(@encoding)
         rescue Encoding::UndefinedConversionError, Encoding::InvalidByteSequenceError
-          string.encode(@encoding, ENCODE_UNCONVERTABLE_BYTES)
+          encode_unconvertable_bytes(string)
         rescue Encoding::ConverterNotFoundError
-          string.dup.force_encoding(@encoding).encode(ENCODE_NO_CONVERTER)
+          encode_no_converter(string.dup.force_encoding(@encoding))
         end
 
+        private
+
+        # On Ruby 2.7.0 keyword arguments mixed with conventional cause a warning to
+        # be issued requiring us to be explicit by using a ** to pass the hash as
+        # keyword arguments. Any keyword argument supporting Ruby supports this.
+        if RubyFeatures.kw_args_supported?
+          # Note on non keyword supporting Ruby ** causes a syntax error hence
+          # we must use eval. To be removed in RSpec 4.
+          eval(<<-CODE, __LINE__, __FILE__)
+          def encode_unconvertable_bytes(string)
+            string.encode(@encoding, **ENCODE_UNCONVERTABLE_BYTES)
+          end
+
+          def encode_no_converter(string)
+            string.encode(**ENCODE_NO_CONVERTER)
+          end
+          CODE
+        else
+          def encode_unconvertable_bytes(string)
+            string.encode(@encoding, ENCODE_UNCONVERTABLE_BYTES)
+          end
+
+          def encode_no_converter(string)
+            string.encode(ENCODE_NO_CONVERTER)
+          end
+        end
+
+        public
+
         # Prevents raising ArgumentError
         if String.method_defined?(:scrub)
           # https://github.com/ruby/ruby/blob/eeb05e8c11/doc/NEWS-2.1.0#L120-L123