Reline not offering completions on empty input

[ddoherty03]

At the prompt, if a user just types TAB, I want to display all completions available. It appears that reline only displays completions if there is something typed at the prompt.

Here is an example that illustrates the issue from ChatGPT:

#!/usr/bin/env ruby

require 'reline'

# Force Emacs mode so that Tab completion is the standard behavior
# (In some Reline versions these are just methods, not setters)
Reline.emacs_editing_mode

# A debug completion function that prints when it's called:
def debug_completion(input)
  warn "[DEBUG] completion_proc called with '#{input.inspect}'"
  if input.empty?
    %w[apple banana cherry]
  else
    %w[apple banana cherry].grep(/^#{Regexp.escape(input)}/)
  end
end

Reline.completion_proc = method(:debug_completion)

loop do
  line = Reline.readline("> ", true)
  break if line.nil? || line.strip.downcase == "exit"
  puts "You typed: #{line}"
end

Hitting TAB and nothing else at the prompt should offer 'apple', 'banana', and 'cherry', but it offers nothing.

[tompng]

This is an incompatibility with Readline. GNU Readline (gem readline-ext) shows candidates.

require 'readline'
p Readline => Readline::VERSION #=> {Readline=>"8.2"}
Readline.completion_proc = proc { |target| %w[apple banana cherry] }
Readline.readline('> ', true)