Subject: bug#65468: 29.1; describe-theme fails to describe some themes not loaded

From: Thierry Volpiatto <[email-masked]>
Date: Wed, 23 Aug 2023 11:01:50 +0000

Mauro Aranda <[email-masked]> writes:

> Thierry Volpiatto <[email-masked]> writes:
>
>> This because `describe-theme-1` is not looping in buffer to find
>> `deftheme` definition.
>
> It is a convention that the first form should be a call to deftheme.
> But it seems built-in themes have deviated from that convention.  And
> other themes might as well, I don't know.

Maybe.

>>
>> Try (describe-theme 'leuven) to reproduce (if not already loaded of
>   course).
>>
>
> At least for the leuven themes, it should be easy to make them follow
> the convention.

Yes.

>> This patch fixes it:
>>
>> diff --git a/lisp/cus-theme.el b/lisp/cus-theme.el
>> index 5d3f2585976..3640d1ec329 100644
>> --- a/lisp/cus-theme.el
>> +++ b/lisp/cus-theme.el
>> @@ -513,13 +513,15 @@ It includes all faces in list FACES."
>>        ;; Attempt to grab the theme documentation
>>        (when fn
>>  	(with-temp-buffer
>> -	  (insert-file-contents fn)
>> -	  (let ((sexp (let ((read-circle nil))
>> -			(condition-case nil
>> -			    (read (current-buffer))
>> -			  (end-of-file nil)))))
>> -            (and (eq (car-safe sexp) 'deftheme)
>> -		 (setq doc (nth 2 sexp)))))))
>> +          (insert-file-contents fn)
>> +          (catch 'found
>> +            (let (sexp)
>> +              (while (setq sexp (let ((read-circle nil))
>> +	                          (condition-case nil
>> +		                      (read (current-buffer))
>> +		                    (end-of-file nil))))
>> +                (when (eq (car-safe sexp) 'deftheme)
>> +	          (throw 'found (setq doc (nth 2 sexp))))))))))
>>      (princ "\n\nDocumentation:\n")
>>      (princ (if (stringp doc)
>>  	       (substitute-command-keys doc)
>>
>> However for the modus themes it will fail as well because deftheme is
>> nested inside a eval-when-compile.
>
> I feel like if there are more themes that suffer from this problem,
> they could solve it by following the convention.

For the themes that are in Emacs, should be easy to fix.

> And for other themes, it seems like either way we have to give it more
> thought, because AFAICS following the convention is more difficult and
> the patch doesn't solve it either.

It seems the themes installed from package are already loaded, not sure
if it is true for all of them though.

For what is `describe-theme-1` patch is is always better to cover more
use cases even if not all cases are covered (e.g. modus themes), however
having a new function that fetch documentation from file would be great
and reusable elsewhere (I have here - in helm - to write my own function to get the
first line documentation of a theme).

>
>> And while I am at it, the docstring of Leuven-dark is wrong (guess it has
>> been copy/pasted from Leuven without modifications).
>
> This has been fixed already, thanks.

Good, thanks.

-- 
Thierry