Stop using Bubble in coherence and instead emulate it with an intercr…

…ate check
rust-lang · matthiaskrgr · Dec 16, 2023 · Feb 28, 2024 · Feb 21, 2024 · Feb 23, 2024
commit 836ac98482ff93853dbf3aeb2d67ce5253f4b2e0
diff --git a/compiler/rustc_infer/src/infer/opaque_types.rs b/compiler/rustc_infer/src/infer/opaque_types.rs
@@ -105,6 +105,16 @@ impl<'tcx> InferCtxt<'tcx> {
         let process = |a: Ty<'tcx>, b: Ty<'tcx>, a_is_expected| match *a.kind() {
             ty::Alias(ty::Opaque, ty::AliasTy { def_id, args, .. }) if def_id.is_local() => {
                 let def_id = def_id.expect_local();
+                if self.intercrate {
+                    // See comment on `insert_hidden_type` for why this is sufficient in coherence
+                    return Some(self.register_hidden_type(
+                        OpaqueTypeKey { def_id, args },
+                        cause.clone(),
+                        param_env,
+                        b,
+                        a_is_expected,
+                    ));
+                }
                 match self.defining_use_anchor {
                     DefiningAnchor::Bind(_) => {
                         // Check that this is `impl Trait` type is
@@ -146,8 +156,10 @@ impl<'tcx> InferCtxt<'tcx> {
                         }
                     }
                     DefiningAnchor::Bubble => {}
-                    DefiningAnchor::Error => return None,
-                };
+                    DefiningAnchor::Error => {
+                        return None;
+                    }
+                }
                 if let ty::Alias(ty::Opaque, ty::AliasTy { def_id: b_def_id, .. }) = *b.kind() {
                     // We could accept this, but there are various ways to handle this situation, and we don't
                     // want to make a decision on it right now. Likely this case is so super rare anyway, that

diff --git a/compiler/rustc_trait_selection/src/traits/coherence.rs b/compiler/rustc_trait_selection/src/traits/coherence.rs
@@ -26,7 +26,6 @@ use rustc_infer::traits::{util, TraitEngine, TraitEngineExt};
 use rustc_middle::traits::query::NoSolution;
 use rustc_middle::traits::solve::{CandidateSource, Certainty, Goal};
 use rustc_middle::traits::specialization_graph::OverlapMode;
-use rustc_middle::traits::DefiningAnchor;
 use rustc_middle::ty::fast_reject::{DeepRejectCtxt, TreatParams};
 use rustc_middle::ty::visit::{TypeVisitable, TypeVisitableExt};
 use rustc_middle::ty::{self, Ty, TyCtxt, TypeSuperVisitable, TypeVisitor};
@@ -190,7 +189,6 @@ fn overlap<'tcx>(
 
     let infcx = tcx
         .infer_ctxt()
-        .with_opaque_type_inference(DefiningAnchor::Bubble)
         .skip_leak_check(skip_leak_check.is_yes())
         .intercrate(true)
         .with_next_trait_solver(tcx.next_trait_solver_in_coherence())