Add a lint for unused self

[james9909]

changelog: Adds a new lint: unused_self

Closes #4550.

[iddm]

I'd also add a negative test, at least for traits - that we don't lint unused_self within traits.

[james9909]

There's already a test for the Debug trait, should I add more?

[bors]

☔ The latest upstream changes (presumably #4625) made this pull request unmergeable. Please resolve the merge conflicts.

[iddm]

There's already a test for the Debug trait, should I add more?

Sorry, missed it. If you mean this:

mod not_applicable {
    use std::fmt;

    struct A {}

    impl fmt::Debug for A {
        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
            write!(f, "A")
        }
    }

    impl A {
        fn method(x: u8, y: u8) {}
    }
}

Then I have a question - does your implementation checks only impl or trait as well?
What about this code, how will it work?

trait A {
    fn method(&self) -> u64 { }
}

Will unused self be linted? Just to be sure. Thanks!

[flip1995]

Impl LGTM. Can you remove the file tests/ui/unused_self.stdout?

Also once this lint is pedantic, it should be possible to remove the allows from the unrelated tests.

[james9909]

Will unused self be linted? Just to be sure. Thanks!

No, the lint here won't be triggered but I'll add this to the tests.

[flip1995]

Thanks!

[bors]

☔ The latest upstream changes (presumably #4602) made this pull request unmergeable. Please resolve the merge conflicts.

[bors]

☔ The latest upstream changes (presumably #4560) made this pull request unmergeable. Please resolve the merge conflicts.

[flip1995]

Rebased to get rid of the merge commits. Thanks for implementing this lint!

@bors r+

[bors]

📌 Commit adf5886 has been approved by flip1995

[bors]

⌛ Testing commit adf5886 with merge 55e7818...

[bors]

☀️ Test successful - checks-travis, status-appveyor
Approved by: flip1995
Pushing 55e7818 to master...