Introduce Vim's options feature, and add :set & :cd

[fukamachi]

Quick troubleshooting

Q. Why does the :e command no longer complete from the directory of the file being edited?

It is to make Lem's vi-mode closer to Vim's behavior. If you prefer the previous behavior, there's 2 options to achieve:

A1. Turn autochdir option on

Set autochdir to t in your init.lisp:

;; Originally, this code should work, but I found a problem later and fixed at #950 
;; (setf (lem-vi-mode:autochdir) t)

;; After #950 is merged
(setf (lem-vi-mode:vi-option-value "autochdir") t)

To change the option temporarily, just execute :set autochdir (and :set noautochdir to turn off).

A2. Change the current directory manually

Use :cd command to change the directory manually:

" Move to "extensions/vi-mode"
:cd extensions/vi-mode
" `%:h` expands to the directory of the current buffer's file
:cd %:h
" `-` means the previous directory
:cd -

Changes

• Add Vim's options feature
  • Currently only autochdir is implemented
    • Works when running :e (find-file) or switching the buffer/window
• [Incompatible changes] Change the base directory to find with :e to the current directory
  • You need to change the directory manually with :cd
    • :cd %:h moves to the current buffer's directory (See "filename modifiers" below)
  • Or, turn autochdir option on
• Add "filename modifiers" which would be expanded in :e, :vs, :sp, and :cd
  • Examples:
    • %: The current buffer's file path
    • %:p: The absolute pathname of the current buffer's file path
    • %:h: The current buffer's directory
    • %:e: The file extension of the current buffer's file
    • %:t: The filename of the current buffer's file
    • %:r: The root of the filename
• Add :cd for changing the current directory
  • :cd <dir> moves to the <dir>
  • :cd moves to the home directory
  • :cd - moves to the previous directory
• Add :set (also :se works)
  • Examples:
    • Turn on: :set autochdir, :set acd, :set acd=t
    • Turn off: :set noautochdir, :set noacd, :set acd=nil
    • Toggle: :set invautochdir, :set autochdir!, :set invacd, :set acd!
    • Get the current value: :set autochdir, :set acd?
    • Reset to the default: :set autochdir&, :set acd&
  • In init.lisp
    • (setf (lem-vi-mode:autochdir) t)

[fukamachi]

We may need filename modifiers, too, like :cd %:h to move to the buffer's directory.

[cxxxr]

Thank you for the PR.
I made a few petty comments, but it seems like a very good change.

[cxxxr]

What about using show-message instead of message and message-timeout?

(lem:show-message (format ...) :timeout ...)

[cxxxr]

we use keywords for package-designator in this project, so it would be nice to see it unified.

[cxxxr]

Perhaps there is an issue that does not apply to windows that are split after this.
It might be a good idea to have the issue.

[fukamachi]

I tried some cases on my machine, but it seems to be working. I don't know why.

[cxxxr]

error is handled as an internal error.
Instead of treating user input as an internal error, it may be better to use editor-error or a condition that inherits from it.

[cxxxr]

Please let me know when you are done making changes.

[cxxxr]

I think it's good.
Thanks for the interesting PR.