email/notmuch: remove mbsync & mbsync-xdg backends

Also merges the +notmuch-sync-command variable into
+notmuch-sync-backend, which now accepts a string.

Mentioned in #4838

modules/email/notmuch/autoload.el

@@ -24,23 +24,33 @@
 
 ;;;###autoload
 (defun +notmuch/quit ()
+  "TODO"
   (interactive)
   ;; (+popup/close (get-buffer-window "*notmuch-hello*"))
   (doom-kill-matching-buffers "^\\*notmuch")
   (+workspace/delete "*MAIL*"))
 
-(defun notmuch-get-sync-command ()
-  (let ((afew-cmd "afew -a -t")
-        (sync-cmd (pcase +notmuch-sync-backend
+(defun +notmuch-get-sync-command ()
+  "Return a shell command string to synchronize your notmuch mmail with."
+  (let* ((afew-cmd "afew -a -t")
+         (sync-cmd
+          (pcase +notmuch-sync-backend
             (`gmi
              (concat "cd " +notmuch-mail-folder " && gmi sync && notmuch new"))
-                    (`mbsync
-                     "mbsync -a && notmuch new")
-                    (`mbsync-xdg
-                     "mbsync -c \"$XDG_CONFIG_HOME\"/isync/mbsyncrc -a && notmuch new")
+            ((or `mbsync
+                 `mbsync-xdg) ; DEPRECATED `mbsync-xdg' is now just `mbsync'
+             (format "mbsync %s -a && notmuch new"
+                     (if-let (config-file
+                              (doom-glob (or (getenv "XDG_CONFIG_HOME")
+                                             "~/.config")
+                                         "isync/mbsyncrc"))
+                         (format "-c %S" config-file)
+                       "")))
             (`offlineimap
              "offlineimap && notmuch new")
-                    (`custom +notmuch-sync-command))))
+            ((and (pred stringp) it) it)
+            (_ (user-error "Invalid notmuch backend specified: %S"
+                           +notmuch-sync-backend)))))
     (if (featurep! +afew)
         (format "%s && %s" sync-cmd afew-cmd)
       sync-cmd)))
@@ -49,7 +59,7 @@
 (defun +notmuch/update ()
   "Sync notmuch emails with server."
   (interactive)
-  (with-current-buffer (compile (notmuch-get-sync-command))
+  (with-current-buffer (compile (+notmuch-get-sync-command))
     (let ((w (get-buffer-window (current-buffer))))
       (select-window w)
       (add-hook

modules/email/notmuch/config.el

@@ -6,10 +6,21 @@
   "Function for customizing the landing page for doom-emacs =notmuch.")
 
 (defvar +notmuch-sync-backend 'gmi
-  "Which backend to use. Can be either gmi, mbsync, offlineimap or nil (manual).")
+  "Which backend to use to synchrone email.
+Accepts a symbol or a shell command string.
 
-(defvar +notmuch-sync-command nil
-  "Command for custom notmuch sync")
+More specifically, this accepts one of the following symbols (see
+`+notmuch-get-sync-command' definition for details):
+
+  `gmi'         Use gmailieer (https://github.com/gauteh/lieer)
+  `mbsync'      Use isync (https://isync.sourceforge.io)
+  `offlineimap' Use offlineimap (https://www.offlineimap.org)
+
+OR a shell command string such as
+
+  \"path/to/some/shell-script.sh\"
+  \"offlineimap && notmuch new && afew -a -t\"
+  \"mbsync %s -a && notmuch new && afew -a -t\"")
 
 (defvar +notmuch-mail-folder "~/.mail/account.gmail"
   "Where your email folder is located (for use with gmailieer).")