fix(resolve): Warn on Self-Type Lifetime Elision for Non-Self Types

[TKanX]

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Summary

FCW lint self_lifetime_elision_not_applicable: fires when a self parameter contains & but does not syntactically contain Self.

Tracking: #140611

Context

Self-type lifetime elision in rustc_resolve relies on a name-matching hack (is_self_ty) that shallow-compares Res values between the self parameter type and the impl self type. As @compiler-errors identified in #140611, this hack cannot see through type aliases (different Res) and only fires for Struct|Union|Enum|PrimTy impls (excludes TyAlias). When it misses, find_lifetime_for_self returns Empty, self-elision silently fails, and a later parameter's lifetime may leak into the return type.

@lcnr proposed restricting self-elision to genuine Self and FCW'ing everything else. This PR implements that.

Behavior

pub struct W<'a>(&'a ());
pub type Alias<'a> = W<'a>;

Case	Code	Before	After
f1	impl Alias { fn f(self: &W) -> &() }	silent wrong '_	FCW
f2	impl Alias { fn f(self: &Alias) -> &() }	silent wrong '_	FCW
f3	impl Alias { fn f(&self) -> &() }	correct	unchanged
f4	impl W { fn f(self: &W) -> &() }	correct (hack fires)	FCW
f5	impl W { fn f(self: &Alias) -> &() }	silent wrong '_	FCW
f6	impl W { fn f(&self) -> &() }	correct	unchanged

A follow-up PR will remove the hack after a warning period.

r? @lcnr
cc @compiler-errors @traviscross

[rustbot]

Some changes occurred in compiler/rustc_hir/src/attrs

cc @jdonszelmann, @JonathanBrouwer

[lcnr]

before discussing this in a lang meeting, can you extend the PR description a bit to summarize the reasoning and discussion behind this?

[rust-bors]

💔 Test for b9f802f failed: CI

[rustbot]

Reminder, once the PR becomes ready for a review, use @rustbot ready.

[rust-bors]

@TKanX: 🔑 Insufficient privileges: not in try users

[traviscross]

@bors try

[rust-bors]

☀️ Try build successful (CI)
Build commit: 3960581 (39605810efb1a0d52f955bfba9e4eec7a01d5deb, parent: fd0c901b00ee1e08a250039cdb90258603497e20)

[traviscross]

@craterbot check

[craterbot]

👌 Experiment pr-153692 created and queued.
🤖 Automatically detected try build 3960581
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[rust-bors]

☔ The latest upstream changes (presumably #154123) made this pull request unmergeable. Please resolve the merge conflicts.