Subject: bug#65872: [PATCH] Fix interactive display of MIME parts

From: Davide Masserut <[email-masked]>
Date: Mon, 11 Sep 2023 19:24:14 +0200

Tags: patch

This patch fixes a bug that did not allow to view attachments after
choosing to display them within Emacs.

The issue is in mm-interactively-view-part, which is used by
gnus-article-interactively-view-part and
notmuch-show-interactively-view-part.

mailcap-mime-info may return a list of functions or strings containing
external commands.  This list is passed to completing-read, which always
returns a string.

Before this change, when the method is a string, mm-display-external
would have attempted to execute it through a shell even when the method
refers to an Elisp function.

I discovered this bug while using notmuch with
notmuch-show-part-button-default-action set to
#'notmuch-show-interactively-view-part and having tried to open a pdf
with doc-view-mode.  This bug should also be reproducible using Gnus
but I don't know how to do it.

In GNU Emacs 30.0.50 (build 24, x86_64-pc-linux-gnu, GTK+ Version
 3.24.38, cairo version 1.17.8) of 2023-09-11 built on T480s
Repository revision: b3ef1d67919261c3af3e12c14f3d66c4d156cc19
Repository branch: master
System Description: Arch Linux

Configured using:
 'configure -C --prefix /home/davide/.local --with-pgtk
 --with-native-compilation --enable-link-time-optimization
 --enable-locallisppath=/usr/share/emacs/site-lisp/
 'CFLAGS=-march=native -O2''

>From 9f45d1b4c06bea2ffca7f7575f7600e8530b3814 Mon Sep 17 00:00:00 2001
From: Davide Masserut <[email-masked]>
Date: Mon, 11 Sep 2023 16:49:21 +0200
Subject: [PATCH] Fix interactive display of MIME parts

mailcap-mime-info may return a list of functions or strings containing
external commands.  This list is passed to completing-read, which
always returns a string.

Before this change, when the method is a string, mm-display-external
would have attempted to execute it through a shell even when the
method refers to an Elisp function.

* lisp/gnus/mm-decode.el (mm-interactively-view-part): When method
contains a valid symbol, extract it using intern.
---
 lisp/gnus/mm-decode.el | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lisp/gnus/mm-decode.el b/lisp/gnus/mm-decode.el
index b9beedf6c5c..1f91491afa1 100644
--- a/lisp/gnus/mm-decode.el
+++ b/lisp/gnus/mm-decode.el
@@ -1501,7 +1501,7 @@ mm-interactively-view-part
     (when (string= method "")
       (error "No method given"))
     (if (string-match "^[^% \t]+$" method)
-	(setq method (concat method " %s")))
+        (setq method (or (intern-soft method) (concat method " %s"))))
     (mm-display-external handle method)))
 
 (defun mm-preferred-alternative (handles &optional preferred)
-- 
2.42.0