Auto merge of #11938 - GuillaumeGomez:unconditional_recursion, r=llogiq

Add new `unconditional_recursion` lint

Currently, rustc `unconditional_recursion` doesn't detect cases like:

```rust
enum Foo {
    A,
    B,
}

impl PartialEq for Foo {
    fn eq(&self, other: &Self) -> bool {
        self == other
    }
}
```

This is because the lint is currently implemented only for one level, and in the above code, `self == other` will then call `impl PartialEq for &T`, escaping from the detection. The fix for it seems to be a bit tricky (I started investigating potential solution to add one extra level of recursion [here](https://github.com/rust-lang/rust/compare/master...GuillaumeGomez:rust:trait-impl-recursion?expand=1) but completely broken at the moment).

I expect that this situation will remain for a while. In the meantime, I think it's acceptable to check it directly into clippy for the time being as a lot of easy cases like this one can be easily checked (next I plan to extend it to cover other traits like `ToString`).

changelog: Add new `unconditional_recursion` lint

1 files changed, 1 insertions, 0 deletions

diff --git a/clippy_lints/src/declared_lints.rs b/clippy_lints/src/declared_lints.rs
index 1220eb89013..546a100f9a4 100644
--- a/clippy_lints/src/declared_lints.rs
+++ b/clippy_lints/src/declared_lints.rs
@@ -676,6 +676,7 @@ pub(crate) static LINTS: &[&crate::LintInfo] = &[
     crate::types::REDUNDANT_ALLOCATION_INFO,
     crate::types::TYPE_COMPLEXITY_INFO,
     crate::types::VEC_BOX_INFO,
+    crate::unconditional_recursion::UNCONDITIONAL_RECURSION_INFO,
     crate::undocumented_unsafe_blocks::UNDOCUMENTED_UNSAFE_BLOCKS_INFO,
     crate::undocumented_unsafe_blocks::UNNECESSARY_SAFETY_COMMENT_INFO,
     crate::unicode::INVISIBLE_CHARACTERS_INFO,