Re: how to track down "invalid face attribute" errors?

[Felix Dietrich <felix.dietrich@sperrhaken.name>]

Hello Robert,

Emanuel Berg <incal@dataswamp.org> writes:
>
> Eric S Fraga <e.fraga@ucl.ac.uk> writes:
>
>> some package I'm using is leading to errors of the form
>> 
>>   Invalid face attribute :foreground nil [54 times]
>> 
>> can anybody suggest how I can track down which package/function is
>> causing this?  Debugging on error doesn't catch this.
>
> Sounds like that error message should be changed to include
> what face causes trouble, if possible?


Robert Pluim <rpluim@gmail.com> writes:
>
> Felix Dietrich <felix.dietrich@sperrhaken.name> writes:
>
>> Robert Pluim <rpluim@gmail.com> writes:
>>>
>>> (If you have a reproducer, we can look at changing the message)
>>
>> Here is one:
>>
>> #+begin_src emacs-lisp
>>   (let ((buf (generate-new-buffer "*test*"))
>>         (s (propertize "Hello World" 'face '(:foreground nil))))
>>     (with-current-buffer buf
>>       (insert s))
>>     (display-buffer buf))
>> #+end_src
>
> Thereʼs no actual face there for Emacs to log, what the low-level code
> receives is "(:foreground nil)"

But “xfaces.c:merge_face_ref” (which produces the error message) has a
“struct window w” parameter.  I believe in cases where it is not NULL,
which it isnʼt when running the above code, this could be used to derive
the buffer and the bufferʼs position using the struct members “contents”
and “pointm’: 1. “contents” stores, for leaf windows, the windows
buffer; its descriptions mentions other possible value types it may hold
[1]; I do not know in how far these other types have to be considered
here.  2. “pointm” refers to a marker holding the current buffer
position in window; its description states that it is “used only when
the window is not selected”.  Therefore, it is possible that, if the
window “w” is the selected one, the point would have to be taken from
another source (perhaps the “PT” macro in “buffer.h”).

Also note that, if the position would be added to the log entry,
multiple log entries would not be merged anymore.  Additionally, with
the code above, the position is actually after the text (at
‘point-max’); therefore, this might not be useful information to add.

I am not sure if the whole thing is worth the effort or would complicate
the creation of a simple log entry for a, hopefully, rare case to much.

Anyway, perhaps, if there is any interest in adding information to the
“Invalid face attribute” log message, further discussion should move to
a wishlist bug report?


Robert Pluim <rpluim@gmail.com> writes:
>
> Felix Dietrich <felix.dietrich@sperrhaken.name> writes
>>
>> Upon evaluation, the resulting output in the “*Messages*” buffer also
>> shows another issues with a missing newline between messages (in Emacs
>> 28.1 at least).
>
>> #+begin_example
>> #<window 54 on *test*<2>>Invalid face attribute :foreground nil
>> Invalid face attribute :foreground nil
>> #+end_example
>
> Itʼs still there in emacs-29, but itʼs deep in the guts of the elisp
> engine, so I havenʼt found exactly where it comes from.

If there isnʼt one already, I try to remember to file a minor bug report
sometime in the next couple of days.


>> Maybe a value of nil for the :foreground attribute in an anonymous face
>> should be handled the same way as it is in a face defined with
>> ‘defface’, that is being treated as the symbol ‘unspecified’?
>
>> #+begin_src emacs-lisp
>>   (progn
>>     (defface my/test '((t . (:foreground nil))) "test face")
>>     (face-attribute 'my/test :foreground))
>> #+end_src
>
>> #+RESULTS:
>> : unspecified
>
> There was recently a long thread about this on emacs-devel, which I
> didnʼt read :-) It might be worth suggesting this there.

I donʼt seem to be able to find it.


Footnotes:
[1]  “For a leaf window or a tooltip window this is the buffer shown
      in the window; for a combination window this is the first of
      its child windows; for a pseudo window showing the menu bar or
      tool bar this is nil.  It is a buffer for a minibuffer window
      as well.”
      — Description of the “contents” member of “struct window”
        copied from the file “window.h”

-- 
Felix Dietrich