fix: don't crash on utf18 autocompletion

fixes #52

Author: alexanderadam

lib/irb/completion.rb

@@ -275,7 +275,7 @@ def retrieve_completion_data(input, bind:, doc_namespace:)
           nil
         else
           sym = $1
-          candidates = Symbol.all_symbols.collect do |s|
+          candidates = Symbol.all_symbols.filter_map do |s|
             s.inspect
           rescue EncodingError
             # ignore
@@ -453,6 +453,13 @@ def retrieve_completion_data(input, bind:, doc_namespace:)
         else
           candidates = (bind.eval_methods | bind.eval_private_methods | bind.local_variables | bind.eval_instance_variables | bind.eval_class_constants).collect{|m| m.to_s}
           candidates |= RubyLex::RESERVED_WORDS.map(&:to_s)
+
+          target_encoding = Encoding.default_external
+          candidates = candidates.compact.filter_map do |candidate|
+            candidate.encoding == target_encoding ? candidate : candidate.encode(target_encoding)
+          rescue EncodingError
+            nil
+          end
           candidates.grep(/^#{Regexp.quote(input)}/).sort
         end
       end

test/irb/test_completion.rb

@@ -343,5 +343,21 @@ def test_regexp_completor_handles_encoding_errors_gracefully
         Encoding.default_external = original_encoding
       end
     end
+
+    def test_utf16_method_name_does_not_crash
+      # Reproduces issue #52: https://github.com/ruby/irb/issues/52
+      method_name = "test_utf16_method".encode(Encoding::UTF_16)
+      test_obj = Object.new
+      test_obj.define_singleton_method(method_name) {}
+      test_bind = test_obj.instance_eval { binding }
+
+      completor = IRB::RegexpCompletor.new
+      result = nil
+      assert_nothing_raised do
+        result = completor.completion_candidates('', 'test', '', bind: test_bind)
+      end
+      
+      assert_include result, "test_utf16_method"
+    end
   end
 end