Rollup merge of #109166 - lcnr:define_opaque_types-explicit, r=oli-obk

make `define_opaque_types` fully explicit

based on the idea of #108389. Moved `define_opaque_types` into the actual operations, e.g. `eq`, instead of `infcx.at` because normalization doesn't use `define_opaque_types` and even creates it's own `At` with a different `define_opaque_types` internally.

Somewhat surprisingly, coherence actually relies on `DefineOpaqueTypes::Yes` for soundness which was revealed because I've incorrectly used `DefineOpaqueTypes::No` in `equate_impl_headers`. It feels concerning that even though this is the case, we still sometimes use `DefineOpaqueTypes::No` in coherence. I did not look into this as part of this PR as it is purely changing the structure of the code without changing behavior in any way.

r? ```@oli-obk```

1 files changed, 2 insertions, 3 deletions

diff --git a/src/librustdoc/clean/blanket_impl.rs b/src/librustdoc/clean/blanket_impl.rs
index bcdbbcacc4b..3a3bf6a7ab9 100644
--- a/src/librustdoc/clean/blanket_impl.rs
+++ b/src/librustdoc/clean/blanket_impl.rs
@@ -1,6 +1,6 @@
 use crate::rustc_trait_selection::traits::query::evaluate_obligation::InferCtxtExt;
 use rustc_hir as hir;
-use rustc_infer::infer::{InferOk, TyCtxtInferExt};
+use rustc_infer::infer::{DefineOpaqueTypes, InferOk, TyCtxtInferExt};
 use rustc_infer::traits;
 use rustc_middle::ty::ToPredicate;
 use rustc_span::DUMMY_SP;
@@ -47,8 +47,7 @@ impl<'a, 'tcx> BlanketImplFinder<'a, 'tcx> {
 
                 // Require the type the impl is implemented on to match
                 // our type, and ignore the impl if there was a mismatch.
-                let cause = traits::ObligationCause::dummy();
-                let Ok(eq_result) = infcx.at(&cause, param_env).eq(impl_trait_ref.self_ty(), impl_ty) else {
+                let Ok(eq_result) = infcx.at(&traits::ObligationCause::dummy(), param_env).eq(DefineOpaqueTypes::No, impl_trait_ref.self_ty(), impl_ty) else {
                         continue
                     };
                 let InferOk { value: (), obligations } = eq_result;