The function set as the value of mu4e-sent-func is not called when sending a message

[benthamite]

Expected or desired behavior

I have defined a function to be called when a message is sent, as follows:

(defun mu4e-extras-mark-sent-as-read (docid _draft-path)
  "Mark the sent message identified by DOCID as read.
When mu4e sends an email with Gmail, Gmail automatically saves a copy in the
\"Sent\" folder, so the local copy is deleted (as specified by
`mu4e-sent-messages-behavior'). However, the saved copy is treated as a new,
unread message when synchronized back to the local client. To handle this
annoyance, this function marks the saved copy as read. It should be set as the
value of `mu4e-sent-func'."
  (mu4e--server-move docid nil "+S-u-N"))

(setq mu4e-sent-func #'mu4e-extras-mark-sent-as-read)

My expectation is that this function will be called after sending a message.

Actual behavior

The function is not called after sending a message.

Steps to reproduce

1. Evaluate the code above.
2. M-x debug-on-entry RET mu4e-extras-mark-sent-as-read
3. M-x compose-new RET.
4. Compose a test message.
5. M-x message-send-and-exit RET.
6. Note that the debugger is not triggered.

Versions of mu, mu4e/emacs, operating system etc.

mu4e 1.12.4
GNU Emacs 29.3 (build 2, aarch64-apple-darwin23.2.0, NS appkit-2487.30 Version 14.2.1 (Build 23C71)) of 2024-04-26
macOS Sonoma 14.4.1

[djcb]

Unfortunately, this is a bit of an unsupported use-case.

mu4e-sent-func is for mu4e's internal plumbing.. well, used to be; it's gone now. There are still a few remnants.
I'd recommend using message-sent-hook instead.

But note that mu4e--server-move is explicitly an internal function.