Eli Zaretskii <eliz@gnu.org> writes:

>> From: Andy Moreton <andrewjmoreton@gmail.com>
>> Date: Thu, 02 May 2019 16:43:31 +0100
>> 
>> > So yes, I think Noam is right, and 'undecided' is a better alternative here.
>> 
>> That is arguing for the existing code, which does not work correctly.
>
> No, the existing code simply uses the undecoded string.
>
> What I argue for is to do this:
>
> diff --git a/lisp/gnus/mm-view.el b/lisp/gnus/mm-view.el
> index 1e1d264b99..173ebfab48 100644
> --- a/lisp/gnus/mm-view.el
> +++ b/lisp/gnus/mm-view.el
> @@ -475,7 +475,7 @@ mm-display-inline-fontify
>  		    (charset
>  		     (mm-decode-string text charset))
>  		    (t
> -		     text)))
> +		     (mm-decode-string text 'undecided))))
>        (let ((font-lock-verbose nil)     ; font-lock is a bit too verbose.
>  	    (enable-local-variables nil))
>          ;; We used to set font-lock-mode-hook to nil to avoid enabling
>
>> I am disinclined to look any further at this, as nobody else appears to
>> be running the existing code before commenting, or testing the proposed
>> patch.
>
> Please don't be offended, there's no intent to offend you here.  Your
> efforts are greatly appreciated.  We are just discussing a small
> change to what you were proposing, see above.
>
> Or are you saying that using undecided as above doesn't do the job?
>
> (Sorry, I don't use Gnus, so to be able to reproduce the problem and
> test a proposed solution I need detailed instructions, I cannot easily
> do it myself without investing an inordinate amount of time.)

FWIW, I use Gnus, and your suggested change to mm-display-inline-fontify
fixes the inline display of the patch in the OP for me.  BTW, the last
two cond branches can be merged following your change: