Add system-file, system-system-file, and change logic around

early-init.el

@@ -54,6 +54,8 @@ See `no-littering' for examples.")
 
 ;; Load system-specific changes.
 (progn (require 'system)
+       (setq system-default-font "DejaVu Sans Mono"
+             system-variable-pitch-font "DejaVu Sans")
        (setq system-load-directory (sync/ "emacs/systems/" t))
        (system-settings-load nil :nowarn))
 

lisp/system.el

@@ -58,6 +58,10 @@ A floating-point number is recommended, since that makes it
 relative to the `default' face height."
   :type 'number)
 
+(defvar system-file nil
+  "The current system's file for system-specific configuration.
+Do not edit this by hand.  Instead, call `system-system-file'.")
+
 ;;; Functions
 
 ;; Convenience functions for systems
@@ -74,40 +78,74 @@ relative to the `default' face height."
 This function is like `warn', except it uses the `system' type."
   (display-warning 'system (apply #'format-message message args)))
 
+(defun system-system-file (&optional system refresh-cache set-system-file-p)
+  "Determine the current system's system-specific file.
+The current system's file will be returned, and the value of
+`system-file' set /unless/ the parameter SYSTEM was passed to
+this function and SET-SYSTEM-FILE-P is nil.  If both SYSTEM and
+SET-SYSTEM-FILE-P are non-nil, this function will still set
+`system-file'.
+
+If SYSTEM is not passed, and `system-file' is set, simply return
+its value /unless/ REFRESH-CACHE is non-nil, in which case
+`system-load-alist' will be looped through to find the
+appropriate system by testing the car of each cell there.  When
+one matches, use the cdr of that cell as SYSTEM.  If none
+matches, return nil.
+
+This function will only look for system-specific files in
+`system-load-directory'."
+  (let* ((system* (or system
+                     (and system-file (not refresh-cache))
+                     (cl-loop for (p . s) in system-load-alist
+                              if (funcall p) return s)))
+        (file (expand-file-name (format "%s" system*) system-load-directory)))
+    (when (or (not system)
+              (and system set-system-file-p))
+      (setq system-file file))
+    file))
+
 ;;;###autoload
 (defun system-settings-load (&optional system error nomessage)
   "Load system settings.
-If optional SYSTEM (a symbol or a string) is not provided, loop
+Load settings from `system-file', or the `system-file' as
-through `system-load-alist', testing the car of each cell there.
+determined by SYSTEM, if passed.  See `system-system-file' for
-When one matches, use the cdr of that cell as SYSTEM.  Either
+details on how the `system-file' is determined.
-way, look in `system-load-directory' for the files to load.
 
-If none match, warn the user.
+ERROR determines how to deal with errors: if nil, warn the user
+when `system-file' can't be found or when the system being used
+can't be determined.  If t, those are elevated to errors.  If any
+other value, the errors are completely ignored.
 
-Optional argument ERROR is similar to in `load', but negated: if
+NOMESSAGE is passed directly to `load'."
-t, it will generate an error; if nil, it will warn the user;
+  (let ((file (system-system-file system)))
-otherwise, if ERROR is anything else, it will be completely
+    (if file
-silent.
-
-NOMESSAGE is passed as-is to `load'."
-  (let ((system (or system
-                    (cl-loop for (p . s) in system-load-alist
-                             if (funcall p)
-                             return s))))
-    (if system
         (condition-case e
-            (load (expand-file-name (format "%s" system) system-load-directory)
+            (load file nil nomessage)
-                  nil nomessage)
           (t (cond ((eq error t) (signal (car e) (cdr e)))
-                   ((null error) (system-warn
+                   ((null error) (system-warn "Couldn't find file `%s'."
-                                  (concat
+                                              file)))))
-                                   "Couldn't find file `%s' to load"
-                                   " (Looked in %s).")
-                                  system system-load-directory)))))
       (funcall (cond ((eq error t) #'error)
                      ((null error) #'system-warn)
                      (t #'ignore))
                "Could not determine the system being used."))))
 
+;;;###autoload
+(defun system-find-system-file (&optional system)
+  "Find the current system's system-file."
+  (interactive (list (completing-read "System file: "
+                                      (mapcar (lambda (a) (format "%s" (cdr a)))
+                                              system-load-alist)
+                                      nil t nil nil
+                                      (cl-loop for (p . s) in system-load-alist
+                                               if (funcall p)
+                                               return (format "%s" s)))))
+  (find-file (cl-loop with file = (system-system-file system)
+                      for cand in (list file
+                                        (concat file ".el"))
+                      if (file-exists-p cand)
+                      return cand
+                      finally return cand)))
+
 (provide 'system)
 ;;; system.el ends here