doc attribute parsing errors: Revert #151952

[GuillaumeGomez]

Reverts #151952.

Since it's now backported with the "future error" warning, we can remove these changes.

r? @JonathanBrouwer

[rustbot]

Some changes occurred in compiler/rustc_attr_parsing

cc @jdonszelmann, @JonathanBrouwer

[JonathanBrouwer]

Can we add tests for the three cases in #151865 (comment)
After that I think this needs T-rustdoc approval since it's a breaking change
@rustbot author

[GuillaumeGomez]

Added the test.

[rustbot]

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

[GuillaumeGomez]

Fixed merge conflict. I'll mention this PR at tonight's meeting.

[GuillaumeGomez]

The rustdoc team decided to keep them as warnings (in this discussion), based on this discussion.

So I'll instead improve the warnings and remove the "future deprecated" part.

[rust-bors]

☔ The latest upstream changes (presumably #152324) made this pull request unmergeable. Please resolve the merge conflicts.