Lisp: Enable #p completion.

.emacs.d/lisp/init-lisp.el

@@ -23,4 +23,28 @@
 (with-eval-after-load 'slime
   (require 'init-slime))
 
+;; #p completion.  See https://github.com/joaotavora/sly/issues/405.
+(with-eval-after-load 'company
+  (defcustom ambrevar/complete-cl-file-prefix "./"
+    "Prefix for `ambrevar/complete-cl-file'."
+    :type 'string)
+
+  (defun ambrevar/complete-cl-file (action &rest _)
+    (interactive (list 'interactive))
+    (cl-case action
+      (interactive (company-begin-backend #'ambrevar/complete-cl-file))
+      (candidates
+       (cond ((and (save-excursion (looking-back "#p" (- (point) 2)))
+                   (not (looking-at-p "\"")))
+              (insert "\"")
+              (save-excursion (insert "\""))
+              (company-files 'candidates ambrevar/complete-cl-file-prefix))
+             ((save-excursion (looking-back "#p\"" (- (point) 3)))
+              (company-files 'candidates ambrevar/complete-cl-file-prefix))))
+      (prefix "")
+      (t (company-files action))))
+
+  (add-to-list 'company-backends 'ambrevar/complete-cl-file)
+  (setq company-backends (cons 'company-files (delete 'company-files company-backends))))
+
 (provide 'init-lisp)