HDUList.verify() "misses" invalid cards?

[josePhoenix]

A colleague reports constructing a FITS file with an invalid header card (ABCDEFGH = unquotedstringliteral ) and seeing unexpected behavior.

On opening:

In [6]: hdul = fits.open('/user/vbajaj/1141601ai_dkc.fits')
WARNING: The following header keyword is invalid or follows an unrecognized non-standard convention:
ABCDEFGH = unquotedstringliteral                                                [astropy.io.fits.card]

However, when calling hdul.verify():

In [21]: hdul.verify('exception')

Calling _verify() on the Card itself similarly does not produce anything. It seems from the comments in the source that returning an empty error list is intentional: https://github.com/astropy/astropy/blob/master/astropy/io/fits/card.py#L1048-L1058

    def _verify(self, option='warn'):
        self._verified = True

        errs = _ErrList([])
        fix_text = ('Fixed {!r} card to meet the FITS '
                    'standard.'.format(self.keyword))

        # Don't try to verify cards that already don't meet any recognizable
        # standard
        if self._invalid:
            return errs

[...]

Thoughts?

(perhaps relevant to #3668)

[josePhoenix]

cc @Vb2341

[mohanagr]

This might be related to #5877 too. I have encountered a couple of issues with opening and updating of FITS file keywords.

[saimn]

@josePhoenix - As you pointed the card is marked as invalid and so it's ignored from the following checks. Which makes sense, since it is useless to verify something that is not valid, and you already get the warning when opening the file. Do you think it would be useful to have another warning/exception when verifying it ?