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Auto merge of #136539 - matthewjasper:late-normalize-errors, r=compiler-errors

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Emit dropck normalization errors in borrowck

Borrowck generally assumes that any queries it runs for type checking will succeed, thinking that HIR typeck will have errored first if there was a problem. However as of #98641, dropck isn't run on HIR, so there's no direct guarantee that it doesn't error. While a type being well-formed might be expected to ensure that its fields are well-formed, this is not the case for types containing a type projection:

```rust
pub trait AuthUser {
    type Id;
}

pub trait AuthnBackend {
    type User: AuthUser;
}

pub struct AuthSession<Backend: AuthnBackend> {
    data: Option<<<Backend as AuthnBackend>::User as AuthUser>::Id>,
}

pub trait Authz: Sized {
    type AuthnBackend: AuthnBackend<User = Self>;
}

pub fn run_query<User: Authz>(auth: AuthSession<User::AuthnBackend>) {}
// ^ No User: AuthUser bound is required or inferred.
```

While improvements to trait solving might fix this in the future, for now we go for a pragmatic solution of emitting an error from borrowck (by rerunning dropck outside of a query) and making drop elaboration check if an error has been emitted previously before panicking for a failed normalization.

Closes #103899
Closes #135039

r? `@compiler-errors` (feel free to re-assign)
This commit is contained in:
bors 2025-02-19 07:49:08 +00:00
commit ed49386d3a
20 changed files with 262 additions and 109 deletions
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17
compiler/rustc_mir_transform/src/elaborate_drop.rs
View file

@ -266,8 +266,21 @@ where
let tcx = self.tcx();
assert_eq!(self.elaborator.typing_env().typing_mode, ty::TypingMode::PostAnalysis);
let field_ty =
tcx.normalize_erasing_regions(self.elaborator.typing_env(), f.ty(tcx, args));
// The type error for normalization may have been in dropck: see
// `compute_drop_data` in rustc_borrowck, in which case we wouldn't have
// deleted the MIR body and could have an error here as well.
let field_ty = match tcx
.try_normalize_erasing_regions(self.elaborator.typing_env(), f.ty(tcx, args))
{
Ok(t) => t,
Err(_) => Ty::new_error(
self.tcx(),
self.elaborator
.body()
.tainted_by_errors
.expect("Error in drop elaboration not found by dropck."),
),
};
(tcx.mk_place_field(base_place, field, field_ty), subpath)
})