Add lint 'ref_option_ref' #1377

[dvermd]

This lint checks for usage of &Option<&T> which can be simplified as Option<&T> as suggested in #1377.

This WIP PR is here to get feedback on the lint as there's more cases to be handled:

• statics/consts,
• associated types,
• type alias,
• function/method parameter/return,
• ADT definitions (struct/tuple struct fields, enum variants)

changelog: Add 'ref_option_ref' lint

[rust-highfive]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @flip1995 (or someone else) soon.

If any changes to this PR are deemed necessary, please add them as extra commits. This ensures that the reviewer can see what has changed since they last reviewed the code. Due to the way GitHub handles out-of-date commits, this should also make it reasonably obvious what issues have or haven't been addressed. Large or tricky changes may require several passes of review and changes.

Please see the contribution instructions for more information.

[flip1995]

I don't think it matters where this pattern occurs and we can lint in any case. Except, we have to be careful in public item signatures, like functions, structs, statics, consts, ...

The simplest way to deal with this is to add check_item and check_item_post and set a flag in your lint struct, if we're in a public item. This will introduce FNs in bodies of public functions. You can try to deal with that yourself in this PR or just write it as a known FN in the Known Problems section and leave it up for future folks.

[dvermd]

I added some limitations to the Know Problems section as advised.

[bors]

☔ The latest upstream changes (presumably #6135) made this pull request unmergeable. Please resolve the merge conflicts.

Note that reviewers usually do not review pull requests until merge conflicts are resolved! Once you resolve the conflicts, you should change the labels applied by bors to indicate that your PR is ready for review. Post this as a comment to change the labels:

@rustbot modify labels: +S-waiting-on-review -S-waiting-on-author

[dvermd]

@rustbot modify labels: +S-waiting-on-review -S-waiting-on-author

[flip1995]

Only a little formatting left to do.

[flip1995]

@bors r+

Thanks!

[bors]

📌 Commit 7b065db has been approved by flip1995

[bors]

⌛ Testing commit 7b065db with merge 2fe87a8...

[bors]

☀️ Test successful - checks-action_dev_test, checks-action_remark_test, checks-action_test
Approved by: flip1995
Pushing 2fe87a8 to master...