feat(lib): backport find-sibling-file

I will slowly phase out projectile in favor of project.el, starting with
projectile-find-other-file, which -- as of Emacs 29 -- has a native
alternative: `find-sibling-file`.

Ref: doomemacs/community#1

modules/config/default/+evil-bindings.el

@@ -677,7 +677,7 @@
        :desc "Configure project"            "g" #'projectile-configure-project
        :desc "Invalidate project cache"     "i" #'projectile-invalidate-cache
        :desc "Kill project buffers"         "k" #'projectile-kill-buffers
-       :desc "Find other file"              "o" #'projectile-find-other-file
+       :desc "Find sibling file"            "o" #'find-sibling-file
        :desc "Switch project"               "p" #'projectile-switch-project
        :desc "Find recent project files"    "r" #'projectile-recentf
        :desc "Run project"                  "R" #'projectile-run-project

modules/editor/evil/+commands.el

@@ -52,7 +52,7 @@
 (evil-ex-define-cmd "pop[up]"     #'+popup/buffer)
 
 ;;; Project navigation
-(evil-ex-define-cmd "a"           #'projectile-find-other-file)
+(evil-ex-define-cmd "a"           #'find-sibling-file)
 (evil-ex-define-cmd "cd"          #'+evil:cd)
 (evil-ex-define-cmd "pwd"         #'+evil:pwd)
 

modules/lang/cc/config.el

@@ -78,6 +78,8 @@ This is ignored by ccls.")
     :return "return"
     :yield "#require")
 
+  (add-to-list 'find-sibling-rules '("/\\([^/]+\\)\\.c\\(c\\|pp\\)\\'" "\\1.\\(h\\|hh\\|hpp\\)"))
+
   (when (modulep! +tree-sitter)
     (add-hook! '(c-mode-local-vars-hook
                  c++-mode-local-vars-hook)

modules/lang/web/+css.el

@@ -8,13 +8,7 @@ be aligned.
 
 If set to `nil', disable all the above behaviors.")
 
-(after! projectile
-  (pushnew! projectile-other-file-alist
-            '("css"  "scss" "sass" "less" "styl")
-            '("scss" "css")
-            '("sass" "css")
-            '("less" "css")
-            '("styl" "css")))
+(add-to-list 'find-sibling-rules '("/\\([^/]+\\)\\.\\(\\(s[ac]\\|le\\)ss\\|styl\\)\\'" "\\1\\.css"))
 
 
 ;;