Update Reline core to stay in sync with the line_editor's completion_append_character

[sjanusz-r7]

Description

When updating Reline.completion_append_character in Reline.completion_proc, the change does not get reflected until you enter a new Reline.readline or Reline.readmultiline context. It seems like the value of Reline.completion_append_character and Reline.line_editor.completion_append_character is out of sync.

Scenario: We are updating the value of Reline.completion_append_character = ' ' inside of the completion_proc, but it's not reflecting in the line_editor

Expected Behaviour

Being able to change Reline.completion_append_character in the completion proc and have it update the line_editor.

i.e. this code:

reline/lib/reline.rb

Lines 83 to 93 in 7534f7f

	def completion_append_character=(val)
	if val.nil?
	@completion_append_character = nil
	elsif val.size == 1
	@completion_append_character = val.encode(encoding)
	elsif val.size > 1
	@completion_append_character = val[0].encode(encoding)
	else
	@completion_append_character = nil
	end
	end

To immediately update the line_editor's completion_append_character value

    def completion_append_character=(val)
      if val.nil?
        @completion_append_character = nil
      elsif val.size == 1
        @completion_append_character = val.encode(encoding)
      elsif val.size > 1
        @completion_append_character = val[0].encode(encoding)
      else
        @completion_append_character = nil
      end
      # Ensure the line_editor is updated too:
      line_editor.completion_append_character = @completion_append_character
    end

Current Behaviour

Changing Reline.completion_append_character in Reline.completion_append_character does not take effect until a new call to Reline.readline.

Terminal Emulator

MacOS

Reline Version

0.5.10

[tompng]

Some configurations are hard to make stay in sync.
For example, this code updates completion_proc itself in completion_proc. It also updates basic_word_break_characters that changes completion target.

def new_proc(a)
  ->k{
    Readline.completion_proc = new_proc(a.succ)
    Readline.basic_word_break_characters = [';', '.'].sample
    [a]
  }
end
Readline.completion_proc = new_proc('a')

This configurations looks stayed in sync in GNU Readline but not in Reline.
However, making completion_proc and basic_word_break_characters stay in sync will significantly impairs code maintainability.

Only changing completion_append_character to be synchronized is not so hard, but I think it is not a good idea to guarantee it to be stay in sync.

In my opinion, it feel like changing completion_append_character inside completion_proc is a hack that only works in the current version of GNU Readline.

[sjanusz-r7]

In my opinion, it feel like changing completion_append_character inside completion_proc is a hack that only works in the current version of GNU Readline.

What would be a more idiomatic Reline solution? For our use case - the scenario is: Some of our completions require a different value for completion_append_character

It looks like currently GNU Readline and RbReadline support this functionality, but it's not supported by Reline unfortunately without a patch to sync the Readline and line_editor values

As a feature request - if there was a different API to tell Reline about individual append characters as part of the completion_proc result that would be great

[tompng]

I think this is a bug that should be fixed an incompatibility to readline only because GNU Readline documents that rl_completion_append_character can be changed from completion function.

From GNU Readline's documentation https://tiswww.case.edu/php/chet/readline/readline.html#index-rl_005fcompletion_005fappend_005fcharacter

When a single completion alternative matches at the end of the command line, this character is appended to the inserted completion text. The default is a space character (‘ ’). Setting this to the null character (‘\0’) prevents anything being appended automatically. This can be changed in application-specific completion functions to provide the “most sensible word separator character” according to an application-specific command line syntax specification. It is set to the default before any application-specific completion function is called, and may only be changed within such a function.

rl_completion_append_character can only be set from completion function and always reset to default value before completion function is called.
Note that the documented behavior is reported as a bug in Ruby's readline binding and carefully fixed. https://bugs.ruby-lang.org/issues/4635.