Feature request: more machine-readable error messages

[foolip]

Bikeshed has a --line-numbers argument which will sometimes print the line an error was associated with. However, it's documented as hacky:

Hacky support for outputting line numbers on all error messages. Disables output, as this is hacky and might mess up your source.

Feature request: use https://www.gnu.org/prep/standards/html_node/Errors.html or something with a consistent pattern for errors, especially including the source file (#1516 is related)

Given that, and ideally being able to print a line number in more cases, it would be straightforward to create a GitHub Action that would annotate the source where the errors are. Proof of concept:
w3c/webdriver-bidi@ccd32f9#annotation_222823575

[tabatkins]

I'm not seeing how anything you're suggesting here would address the hackiness - did you intend them to?

It's hacky because, even tho LXML exposes a lineNumber attribute on its elements, that attribute is always None. The documentation claims it should work and offers no caveats, but it never has, so I dunno. Instead, I run a regex over the lines, looking for things that might be start tags and putting a line-number attribute on them. This, obviously, can misfire on things that are start-tag-like but wouldn't be recognized by the parser, like code in <xmp>; this doesn't affect the accuracy of the line numbers, but it can corrupt your output, thus why I turn off output.

[foolip]

I didn't know in what the hackiness consists, so I thought "ideally being able to print a line number in more cases" would cover it. Sounds like it can also be wrong, then :)

[tabatkins]

Closing this - due to the gradual switchover to my bespoke HTML parser, most error messages now have non-hacky line numbers (and the branch I'm working on right now will add/improve even more).