Mu4e: Add nuance to Gmail-specific behaviour

for the non-gmail accounts out there

modules/email/mu4e/README.org

@@ -36,7 +36,8 @@ via IMAP) and ~mu~ (to index my mail into a format ~mu4e~ can understand).
 #+end_quote
 
 ** Module Flags
-+ ~+gmail~ Enables gmail-specific configuration.
++ ~+gmail~ Enables gmail-specific configuration for mail ~To~ or ~From~ a gmail
+  address, or a maildir with ~gmail~ in the name.
 
 ** Plugins
 + [[https://github.com/jeremy-compostella/org-msg][org-msg]]

modules/email/mu4e/config.el

@@ -325,7 +325,10 @@ Must be set before org-msg is loaded to take effect.")
 (when (featurep! +gmail)
   (after! mu4e
     ;; don't save message to Sent Messages, Gmail/IMAP takes care of this
-    (setq mu4e-sent-messages-behavior 'delete
+    (setq mu4e-sent-messages-behavior
+          (lambda ()
+            (if (string-match-p "@gmail.com\\'" (message-sendmail-envelope-from))
+                'delete 'sent))
 
           ;; don't need to run cleanup after indexing for gmail
           mu4e-index-cleanup nil
@@ -334,6 +337,19 @@ Must be set before org-msg is loaded to take effect.")
           ;; messages don't really "move"
           mu4e-index-lazy-check t)
 
+    (defun +mu4e-msg-gmail-p (msg)
+      (or
+       (string-match-p "gmail"
+                       (cond
+                        ((member (mu4e-message-field msg :to)
+                                 (plist-get mu4e~server-props :personal-addresses))
+                         (mu4e-message-field msg :to))
+                        ((member (mu4e-message-field msg :from)
+                                 (plist-get mu4e~server-props :personal-addresses))
+                         (mu4e-message-field msg :from))
+                        (t "")))
+       (string-match-p "gmail" (mu4e-message-field msg :maildir))))
+
     ;; In my workflow, emails won't be moved at all. Only their flags/labels are
     ;; changed. Se we redefine the trash and refile marks not to do any moving.
     ;; However, the real magic happens in `+mu4e|gmail-fix-flags'.
@@ -342,18 +358,39 @@ Must be set before org-msg is loaded to take effect.")
     (defun +mu4e--mark-seen (docid _msg target)
       (mu4e~proc-move docid (mu4e~mark-check-target target) "+S-u-N"))
 
+    (defvar +mu4e--last-invalid-gmail-action 0)
+
     (delq! 'delete mu4e-marks #'assq)
-    (setf (alist-get 'trash mu4e-marks)
+    (setf (alist-get 'delete mu4e-marks)
+          (list
+           :char '("D" . "✘")
+           :prompt "Delete"
+           :show-target (lambda (target) "delete")
+           :action (lambda (docid msg target)
+                     (if (+mu4e-msg-gmail-p msg)
+                         (progn (message "The delete operation is invalid for Gmail accounts.")
+                                (when (< 2 (- (float-time) +mu4e--last-invalid-gmail-action))
+                                  (sit-for 1))
+                                (setq +mu4e--last-invalid-gmail-action (float-time)))
+                       (mu4e~proc-remove docid))))
+          (alist-get 'trash mu4e-marks)
           (list :char '("d" . "▼")
                 :prompt "dtrash"
                 :dyn-target (lambda (_target msg) (mu4e-get-trash-folder msg))
-                :action #'+mu4e--mark-seen)
+                :action (lambda (docid msg target)
+                          (if (+mu4e-msg-gmail-p msg)
+                              (+mu4e--mark-seen docid msg target)
+                            (mu4e~proc-move docid (mu4e~mark-check-target target) "+T-N"))))
           ;; Refile will be my "archive" function.
           (alist-get 'refile mu4e-marks)
           (list :char '("r" . "▼")
                 :prompt "rrefile"
                 :dyn-target (lambda (_target msg) (mu4e-get-refile-folder msg))
-                :action #'+mu4e--mark-seen))
+                :action (lambda (docid msg target)
+                          (if (+mu4e-msg-gmail-p msg)
+                              (+mu4e--mark-seen docid msg target)
+                            (mu4e~proc-move docid (mu4e~mark-check-target target) "-N")))
+                #'+mu4e--mark-seen))
 
     ;; This hook correctly modifies gmail flags on emails when they are marked.
     ;; Without it, refiling (archiving), trashing, and flagging (starring) email
@@ -361,8 +398,9 @@ Must be set before org-msg is loaded to take effect.")
     ;; are ineffectual otherwise.
     (add-hook! 'mu4e-mark-execute-pre-hook
       (defun +mu4e-gmail-fix-flags-h (mark msg)
-        (pcase mark
+        (when (+mu4e-msg-gmail-p msg)
-          (`trash  (mu4e-action-retag-message msg "-\\Inbox,+\\Trash,-\\Draft"))
+          (pcase mark
-          (`refile (mu4e-action-retag-message msg "-\\Inbox"))
+            (`trash  (mu4e-action-retag-message msg "-\\Inbox,+\\Trash,-\\Draft"))
-          (`flag   (mu4e-action-retag-message msg "+\\Starred"))
+            (`refile (mu4e-action-retag-message msg "-\\Inbox"))
-          (`unflag (mu4e-action-retag-message msg "-\\Starred")))))))
+            (`flag   (mu4e-action-retag-message msg "+\\Starred"))
+            (`unflag (mu4e-action-retag-message msg "-\\Starred"))))))))