Fix needless_borrow causing mutable borrows to be moved

[Jarcho]

fixes #8191

changelog: Fix needless_borrow causing mutable borrows to be moved
changelog: Rename ref_in_deref to needless_borrow
changelog: Suggest removing the borrow on method call receivers in needless_borrow

[rust-highfive]

r? @camsteffen

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[Jarcho]

This now includes all cases covered by ref_in_deref, which lints (&_).field. The description for both would lead one to believe they lint the same thing. Should I just rename it?

[camsteffen]

I think we can remove/deprecate ref_in_deref then?

Tangentially, I noticed the other day that we don't lint (*x).y. I wonder where that could fit.

[Jarcho]

I'm (very slowly) working on an explicit deref lint. It would fit in there whenever that's done.

[Jarcho]

That successfully broke the changelog... Not really sure what to change there.

[camsteffen]

You need to add declare_deprecated_lint! in clippy_lints/src/deprecated_lints.rs and also add a deprecation test in tests/ui/deprecated.rs. Then run cargo dev update_lints and it should be good.

[Jarcho]

That would mean register_renamed can't be used, right?

[camsteffen]

register_renamed would make it so any usage of ref_in_deref counts as needless_borrow. That may or may not be a good thing but I think the lints are different enough that we don't want that? In any case the error message should point to needless_borrow.

[Jarcho]

The description for ref_inderef` is

Checks for references in expressions that use auto dereference.

The description for needless_borrow is

Checks for address of operations (&) that are going to be dereferenced immediately by the compiler.

Those describe exactly the same thing. o the point where anything covered by one and not he other would be a clear false negative. Given that renaming sound like the appropriate thing to do.

[camsteffen]

Okay, good point. So I think you can just add register_renamed by hand. To fix the error, change any ref_in_deref links in the changelog to not be links anymore.

[Jarcho]

I was trying to avoid editing the changelog, but I don't see any other option.

[camsteffen]

One idea for the lint message but otherwise looks good. Please update "changelog" to include the lint rename and added functionality.

[camsteffen]

Squash some commits then will merge!

[camsteffen]

@bors r+

[bors]

📌 Commit c615140 has been approved by camsteffen

[bors]

⌛ Testing commit c615140 with merge 788a8bc...

[bors]

☀️ Test successful - checks-action_dev_test, checks-action_remark_test, checks-action_test
Approved by: camsteffen
Pushing 788a8bc to master...