Reline.add_dialog_proc should not accept nil as proc

[tompng]

If you pass nil to add_dialog_proc, Reline suddenly raise error.

% ruby -rreline -e "Reline.add_dialog_proc(:a,nil);Reline.readmultiline('prompt>'){true}"
prompt>/usr/local/lib/ruby/3.3.0+0/reline/line_editor.rb:583:in `instance_exec': no block given (LocalJumpError)
	from /usr/local/lib/ruby/3.3.0+0/reline/line_editor.rb:583:in `call'
	from /usr/local/lib/ruby/3.3.0+0/reline/line_editor.rb:618:in `call'
        ...

I chage add_dialog_proc not to accept nil
I change to remove dialog_proc when nil is passed.
There was no way to remove dialog_proc before this pull request.

[st0012]

Should we still take nil but make it as unsetting the previously set dialog?

• If :a is set, Reline.add_dialog_proc(:a,nil) removes it from @dialog_proc_list
• If :a is not set, Reline.add_dialog_proc(:a,nil) just does nothing (not adding :a to @dialog_proc_list, ofc)

[tompng]

take nil but make it as unsetting

Thanks! That looks better. I will do it.

I found a code in irb's test that expecting unsetting behavior.

https://github.com/ruby/irb/blob/c2874ec121d8d70b13ba89c2dbdde72961c2f0ce/test/irb/test_input_method.rb#L41-L43

def test_initialization_without_use_autocomplete
  original_show_doc_proc = Reline.dialog_proc(:show_doc)&.dialog_proc
  ...
ensure
  Reline.add_dialog_proc(:show_doc, original_show_doc_proc, Reline::DEFAULT_DIALOG_CONTEXT)
end

I think test was working because original_show_doc_proc was always not nil