GNU bug report logs - #11883
24.1.50; shell-mode doesn't colorize the prompt

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From: miha <at> kamnitnik.top
To: 11883 <at> debbugs.gnu.org
Subject: bug#11883: 24.1.50; shell-mode doesn't colorize the prompt
Date: Sun, 19 Dec 2021 10:48:29 +0100

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Lars Ingebrigtsen <larsi <at> gnus.org> writes:

> Stefan Monnier <monnier <at> IRO.UMontreal.CA> writes:
>
>> The behavior you see is due to the following:
>> - the prompt is highlighted with an overlay that uses
>>   a comint-highlight-prompt face.
>> - "the prompt" is determined dynamically as "the last
>>   non-line-terminated output of the process".
>> - the ansi-color escapes used to be applied using overlays but are now
>>   applied using text-properties.
>>
>> When you use ansi escapes to color the prompt, you clearly have
>> a conflict with the comint-highlight-prompt face that is to be used for
>> the prompt.
>
> The following simple tweak seems to fix the reported issue:
>
> diff --git a/lisp/comint.el b/lisp/comint.el
> index 9e406614b9..3dfb269de4 100644
> --- a/lisp/comint.el
> +++ b/lisp/comint.el
> @@ -2157,9 +2157,9 @@ comint-output-filter
>  		 'comint-highlight-prompt))
>  	      (setq comint-last-prompt
>  		    (cons (copy-marker prompt-start) (point-marker)))
> -	      (font-lock-prepend-text-property prompt-start (point)
> -					       'font-lock-face
> -					       'comint-highlight-prompt)
> +	      (font-lock-append-text-property prompt-start (point)
> +					      'font-lock-face
> +					      'comint-highlight-prompt)
>  	      (add-text-properties prompt-start (point)
>  	                           `(rear-nonsticky
>  	                             ,comint--prompt-rear-nonsticky)))
>

Sorry for late reply. I believe an analogous change should be made in
the function comint-snapshot-last-prompt:

diff --git a/lisp/comint.el b/lisp/comint.el
index 5f99f560cf..3decb80ff0 100644
--- a/lisp/comint.el
+++ b/lisp/comint.el
@@ -2036,7 +2036,7 @@ comint-snapshot-last-prompt
 Freezes the `font-lock-face' text property in place."
   (when comint-last-prompt
     (with-silent-modifications
-      (font-lock-prepend-text-property
+      (font-lock-append-text-property
        (car comint-last-prompt)
        (cdr comint-last-prompt)
        'font-lock-face 'comint-highlight-prompt))

> That is, we don't overwrite the ANSI face properties.
>
> I guess this might also avoid overwriting properties in prompts that use
> ANSI codes?  Which might also be nice.
>
> Would this regress anything?  Anybody got an opinion?
>
> -- 
> (domestic pets only, the antidote for overdose, milk.)
>    bloggy blog: http://lars.ingebrigtsen.no

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