Make message/rfc822 on buttons work again in Gnus

* lisp/gnus/gnus-art.el (gnus-article-mode): Set
mm-inline-message-prepare-function buffer-locally so that it works
both when inlining rfc822 and hitting the MIME button (bug#51388).
(gnus-mime--inline-message): Factor out into own function.
(gnus-mime-display-single): From here.

2 files changed, 24 insertions, 22 deletions

diff --git a/lisp/gnus/gnus-art.el b/lisp/gnus/gnus-art.el
index 930c739a735..6b33680871a 100644
--- a/lisp/gnus/gnus-art.el
+++ b/lisp/gnus/gnus-art.el
@@ -4506,6 +4506,10 @@ commands:
   (gnus-set-default-directory)
   (buffer-disable-undo)
   (setq show-trailing-whitespace nil)
+  ;; Arrange a callback from `mm-inline-message' if we're
+  ;; displaying a message/rfc822 part.
+  (setq-local mm-inline-message-prepare-function
+              #'gnus-mime--inline-message-function)
   (mm-enable-multibyte))
 
 (defun gnus-article-setup-buffer ()
@@ -6041,31 +6045,29 @@ If nil, don't show those extra buttons."
 (defun gnus-mime-display-mixed (handles)
   (mapcar #'gnus-mime-display-part handles))
 
+(defun gnus-mime--inline-message-function (handle charset)
+  (let ((handles
+         (let (gnus-article-mime-handles
+	       ;; disable prepare hook
+	       gnus-article-prepare-hook
+	       (gnus-newsgroup-charset
+                ;; mm-uu might set it.
+	        (unless (eq charset 'gnus-decoded)
+		  (or charset gnus-newsgroup-charset))))
+	   (let ((gnus-original-article-buffer
+                  (mm-handle-buffer handle)))
+	     (run-hooks 'gnus-article-decode-hook))
+	   (gnus-article-prepare-display)
+           gnus-article-mime-handles)))
+    (when handles
+      (setq gnus-article-mime-handles
+	    (mm-merge-handles gnus-article-mime-handles handles)))))
+
 (defun gnus-mime-display-single (handle)
   (let ((type (mm-handle-media-type handle))
 	(ignored gnus-ignored-mime-types)
 	(mm-inline-font-lock (gnus-visual-p 'article-highlight 'highlight))
 	(not-attachment t)
-        ;; Arrange a callback from `mm-inline-message' if we're
-        ;; displaying a message/rfc822 part.
-        (mm-inline-message-prepare-function
-         (lambda (charset)
-           (let ((handles
-                  (let (gnus-article-mime-handles
-	                ;; disable prepare hook
-	                gnus-article-prepare-hook
-	                (gnus-newsgroup-charset
-                         ;; mm-uu might set it.
-	                 (unless (eq charset 'gnus-decoded)
-		           (or charset gnus-newsgroup-charset))))
-	            (let ((gnus-original-article-buffer
-                           (mm-handle-buffer handle)))
-	              (run-hooks 'gnus-article-decode-hook))
-	            (gnus-article-prepare-display)
-                    gnus-article-mime-handles)))
-	     (when handles
-	       (setq gnus-article-mime-handles
-		     (mm-merge-handles gnus-article-mime-handles handles))))))
 	display text
         gnus-displaying-mime)
     (catch 'ignored
diff --git a/lisp/gnus/mm-view.el b/lisp/gnus/mm-view.el
index 56d05c8fa93..d2a6d2cf5d3 100644
--- a/lisp/gnus/mm-view.el
+++ b/lisp/gnus/mm-view.el
@@ -451,7 +451,7 @@ This is only used if `mm-inline-large-images' is set to
 
 (defvar mm-inline-message-prepare-function nil
   "Function called by `mm-inline-message' to do client specific setup.
-It is called with one parameter -- the charset.")
+It is called with two parameters -- the MIME handle and the charset.")
 
 (defun mm-inline-message (handle)
   "Insert HANDLE (a message/rfc822 part) into the current buffer.
@@ -471,7 +471,7 @@ after inserting the part."
 	(narrow-to-region b b)
 	(mm-insert-part handle)
         (when mm-inline-message-prepare-function
-	  (funcall mm-inline-message-prepare-function charset))
+	  (funcall mm-inline-message-prepare-function handle charset))
 	(goto-char (point-min))
 	(unless bolp
 	  (insert "\n"))