Scratching an Itch
Yesterday I had a technological itch. I was configuring a package in Emacs
and had to search for a variable name, the completion system mixed variables and functions together and it was a bit of a chore. Then I thought “how hard can it be to just create a utility function to list all customizable variables?”. An
(sidenote: And then I spent quite some time tinkering of course :))
later my new package, upiv, was born. You can get it from my forgejo instance.
If you are unfamiliar with use-package, it is a very convenient way to configure packages within Emacs. An example of its usage is this configuration of my new upiv package.
emacs-lisp code snippet start
(use-package upiv
:config
(add-to-list 'marginalia-command-categories '(upiv-at-point . variable))
:custom
(upiv-full-form-in-completion nil))emacs-lisp code snippet end
A little search lead me to mapatoms, which basically allows you to call a function on every existing symbol. From t here it is possible to see if something is a custom-variable-p and if it has some form of value boundp. I only wanted variables with a certain prefix, so string-prefix-p was needed. And there it is, a snippet that will list all lsp-ui customizable variables.
emacs-lisp code snippet start
(mapatoms
(lambda (sym)
(let ((sym-name (symbol-name sym)))
(when (and (custom-variable-p sym)
(boundp sym)
(string-prefix-p "lsp-ui" sym-name))
(message "This is a customizable variable %s" sym-name)))))emacs-lisp code snippet end
Then I got the idea to pass this list on to a completing-read-multiple, allowing the user (me!) to select multiple candidates and insert them into my buffer.
emacs-lisp code snippet start
(when-let ((selected-settings (completing-read-multiple
"Insert settings: " candidates nil t)))
;; do the insertion
)emacs-lisp code snippet end
From there on I kept adding small features, such as adding the :custom keyword when needed, making sure it even works when the cursor is in a string or an comment.
My final addition has been to add marginalia support. This means you can pull up the completion list, the default value will be shown in beautiful highlighting and a documentation string is given for better selection.
The final product is shown in the below screencast, where I fist install and setup vertico and marginalia, and then insert a custom variable using my package.
I do ❤️ Emacs and its extendibility.