From 52ef06f79e3f643520d76a9a3381f4c8dbe98a0d Mon Sep 17 00:00:00 2001
From: Timo Wilken
Date: Tue, 14 Nov 2023 20:02:38 +0100
Subject: Load Lisp project automatically when entering REPL

---
 tw/home/files/emacs-init.el | 40 +++++++++++++++++++++++++++++++++++++++-
 1 file changed, 39 insertions(+), 1 deletion(-)

diff --git a/tw/home/files/emacs-init.el b/tw/home/files/emacs-init.el
index f26c790d..be09c4f6 100644
--- a/tw/home/files/emacs-init.el
+++ b/tw/home/files/emacs-init.el
@@ -503,7 +503,8 @@ If CREATE is true and the resulting directory does not exist, create it."
 
 (use-package sly
   :after (evil)
-  :hook (lisp-mode . sly-mode)   ; `common-lisp-mode' is `lisp-mode'.
+  :hook ((lisp-mode . sly-mode)   ; `common-lisp-mode' is `lisp-mode'.
+         (sly-mrepl-mode . tw/resize-repl-window))
   :config
   (evil-define-key '(normal visual) lisp-mode-map
     (kbd "<localleader>C-c") #'sly-interrupt
@@ -871,7 +872,44 @@ For use in `org-latex-classes'."
 (use-package aggressive-indent
   :hook (scheme-mode emacs-lisp-mode common-lisp-mode sh-mode bash-ts-mode))
 
+(defun tw/find-asd-systems (directory)
+  "Return a list of Common Lisp .asd systems found in DIRECTORY."
+  (let ((asd-rx (rx ".asd" eos)))
+    (mapcar (lambda (file)
+              (string-trim-right file asd-rx))
+            (directory-files directory nil asd-rx))))
+
+(defun tw/lisp-project-setup ()
+  "Set up a Lisp REPL for the current project."
+  (when-let ((fname (buffer-file-name))
+             (project-directory
+              (or (locate-dominating-file fname "guix.scm")
+                  (locate-dominating-file fname #'tw/find-asd-systems)
+                  (project-current nil (file-name-directory fname)))))
+    (cd project-directory)
+    (setq-local
+     inferior-lisp-program
+     `(;; If a guix.scm file exists, run Lisp in a Guix shell to get dependencies.
+       ,@(and (file-exists-p (file-name-concat project-directory "guix.scm"))
+              '("guix" "shell" "-Df" "guix.scm" "--"))
+       "sbcl" "--noinform"
+       ;; Load all defined asdf systems using QuickLisp.
+       ,@(mapcan (lambda (system)
+                   (list "--load" (format "%s.asd" system)
+                         "--eval" (format "(ql:quickload '#:%s)" system)))
+                 ;; Heuristic: shorter names are earlier in the dependency tree.
+                 ;; For example, X-test.asd depends on X.asd.
+                 (sort (tw/find-asd-systems project-directory)
+                       (lambda (s1 s2)
+                         (< (length s1) (length s2)))))
+       ;; Assume the project directory name is the name of the main package.
+       "--eval" ,(format "(in-package #:%s)"
+                         (file-name-base
+                          (directory-file-name project-directory)))))))
+
 (use-package inf-lisp
+  :after (lisp-mode)
+  :hook (lisp-mode . tw/lisp-project-setup)
   :custom
   (inferior-lisp-program "sbcl"))
 
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