Auto merge of #123239 - Urgau:dangerous_implicit_autorefs, r=jdonszelmann,traviscross

Implement a lint for implicit autoref of raw pointer dereference - take 2

*[t-lang nomination comment](https://github.com/rust-lang/rust/pull/123239#issuecomment-2727551097)*

This PR aims at implementing a lint for implicit autoref of raw pointer dereference, it is based on #103735 with suggestion and improvements from https://github.com/rust-lang/rust/pull/103735#issuecomment-1370420305.

The goal is to catch cases like this, where the user probably doesn't realise it just created a reference.

```rust
pub struct Test {
    data: [u8],
}

pub fn test_len(t: *const Test) -> usize {
    unsafe { (*t).data.len() }  // this calls <[T]>::len(&self)
}
```

Since #103735 already went 2 times through T-lang, where they T-lang ended-up asking for a more restricted version (which is what this PR does), I would prefer this PR to be reviewed first before re-nominating it for T-lang.

----

Compared to the PR it is as based on, this PR adds 3 restrictions on the outer most expression, which must either be:
   1. A deref followed by any non-deref place projection (that intermediate deref will typically be auto-inserted)
   2. A method call annotated with `#[rustc_no_implicit_refs]`.
   3. A deref followed by a `addr_of!` or `addr_of_mut!`. See bottom of post for details.

There are several points that are not 100% clear to me when implementing the modifications:
 - ~~"4. Any number of automatically inserted deref/derefmut calls." I as never able to trigger this. Am I missing something?~~ Fixed
 - Are "index" and "field" enough?

----

cc `@JakobDegen` `@WaffleLapkin`
r? `@RalfJung`

try-job: dist-various-1
try-job: dist-various-2

1 files changed, 3 insertions, 0 deletions

diff --git a/compiler/rustc_lint/src/lib.rs b/compiler/rustc_lint/src/lib.rs
index 96705e79e0a..b910d6a138e 100644
--- a/compiler/rustc_lint/src/lib.rs
+++ b/compiler/rustc_lint/src/lib.rs
@@ -36,6 +36,7 @@
 
 mod async_closures;
 mod async_fn_in_trait;
+mod autorefs;
 pub mod builtin;
 mod context;
 mod dangling;
@@ -83,6 +84,7 @@ mod utils;
 
 use async_closures::AsyncClosureUsage;
 use async_fn_in_trait::AsyncFnInTrait;
+use autorefs::*;
 use builtin::*;
 use dangling::*;
 use default_could_be_derived::DefaultCouldBeDerived;
@@ -200,6 +202,7 @@ late_lint_methods!(
             PathStatements: PathStatements,
             LetUnderscore: LetUnderscore,
             InvalidReferenceCasting: InvalidReferenceCasting,
+            ImplicitAutorefs: ImplicitAutorefs,
             // Depends on referenced function signatures in expressions
             UnusedResults: UnusedResults,
             UnitBindings: UnitBindings,