feat(format): add :lang emacs-lisp formatter

Introduce a formatter function for emacs-lisp (tracked upstream here
[1]) that tries to preserve as much of what the user wants as possible

[1]: https://github.com/radian-software/apheleia/pull/102

modules/editor/format/config.el

@@ -49,6 +49,21 @@ select buffers.")
 ;;
 ;;; Additional formatters
 
-(after! apheleia-mode
+(after! apheleia
   ;; TODO html-tidy
-  )
+  (cl-defun apheleia--indent-lisp-buffer
+      (&key buffer scratch callback &allow-other-keys)
+    "Format a Lisp BUFFER. Use SCRATCH as a temporary buffer and CALLBACK to
+apply the transformation. For more implementation detail, see
+`apheleia--run-formatter-function'."
+    (with-current-buffer scratch
+      (setq-local indent-line-function
+                  (buffer-local-value 'indent-line-function buffer))
+      (setq-local lisp-indent-function
+                  (buffer-local-value 'lisp-indent-function buffer))
+      (funcall (with-current-buffer buffer major-mode))
+      (goto-char (point-min))
+      (let ((inhibit-message t)
+            (message-log-max nil))
+        (indent-region (point-min) (point-max)))
+      (funcall callback))))

modules/lang/emacs-lisp/config.el

@@ -39,6 +39,7 @@ See `+emacs-lisp-non-package-mode' for details.")
     :documentation #'+emacs-lisp-lookup-documentation)
   (set-docsets! '(emacs-lisp-mode lisp-interaction-mode) "Emacs Lisp")
   (set-ligatures! 'emacs-lisp-mode :lambda "lambda")
+  (set-formatter! 'lisp-indent #'apheleia--indent-lisp-buffer :modes '(emacs-lisp-mode))
   (set-rotate-patterns! 'emacs-lisp-mode
     :symbols '(("t" "nil")
                ("let" "let*")