wrong_self_convention: Match SelfKind::No more restrictively

[nmathewson]

The wrong_self_convention lint uses a SelfKind type to decide
whether a method has the right kind of "self" for its name, or whether
the kind of "self" it has makes its name confusable for a method in
a common trait. One possibility is SelfKind::No, which is supposed
to mean "No self".

Previously, SelfKind::No matched everything except Self, including
references to Self. This patch changes it to match Self, &Self, &mut
Self, Box, and so on.

For example, this kind of method was allowed before:

impl S {
    // Should trigger the lint, because
    // "methods called `is_*` usually take `self` by reference or no `self`"
    fn is_foo(&mut self) -> bool { todo!() }
}

But since SelfKind::No matched "&mut self", no lint was triggered
(see #8142).

With this patch, the code above now gives a lint as expected.

fixes #8142

changelog: [wrong_self_convention] rejects self references in more cases

[rust-highfive]

r? @xFrednet

(rust-highfive has picked a reviewer for you, use r? to override)

[nmathewson]

(FWIW, lintcheck reports that there are are a couple of new positives here; I haven't evaluated whether they are desirable or not.)

[xFrednet]

Looks good to me, thank you very much! I've also looked at the output of lintcheck, we have five new reports which all seem to be correct. This is a very nice fix 👍

I usually use cargo lintcheck --markdown --filter wrong_self_convention to create a markdown file which has the file locations as lints. The usage depends a bit on the setup, just a side note, in case you're interested. These are new correct reports, which all seem correct:

file	lint	message
cargo-0.49.0/src/cargo/core/source/mod.rs:103:18	clippy::wrong_self_convention	"methods called is_* usually take self by reference or no self"
cargo-0.49.0/src/cargo/ops/tree/graph.rs:166:27	clippy::wrong_self_convention	"methods called from_* usually take no self"
cargo-0.49.0/src/cargo/sources/registry/index.rs:441:22	clippy::wrong_self_convention	"methods called is_* usually take self by reference or no self"
xsv-0.13.0/src/config.rs:282:33	clippy::wrong_self_convention	"methods called from_* usually take no self"
xsv-0.13.0/src/config.rs:300:38	clippy::wrong_self_convention	"methods called from_* usually take no self"

[xFrednet]

btw a second side note, you can assign yourself to an issue including @rustbot claim in your comment. That indicates to others that you want to work on that issue 🙃

Thank you very much for this PR 👍

@bors r+

[bors]

📌 Commit 3d41358 has been approved by xFrednet

[bors]

⌛ Testing commit 3d41358 with merge b25dbc6...

[bors]

☀️ Test successful - checks-action_dev_test, checks-action_remark_test, checks-action_test
Approved by: xFrednet
Pushing b25dbc6 to master...