Rollup merge of #130666 - compiler-errors:super-bounds, r=fee1-dead,fmease

Assert that `explicit_super_predicates_of` and `explicit_item_super_predicates` truly only contains bounds for the type itself

We distinguish _implied_ predicates (anything that is implied from elaborating a trait bound) from _super_ predicates, which are are the subset of implied predicates that share the same self type as the trait predicate we're elaborating. This was originally done in #107614, which fixed a large class of ICEs and strange errors where the compiler expected the self type of a trait predicate not to change when elaborating super predicates.

Specifically, super predicates are special for various reasons: they're the valid candidates for trait upcasting, are the only predicates we elaborate when doing closure signature inference, etc. So making sure that we get this list correct and don't accidentally "leak" any other predicates into this list is quite important.

This PR adds some debug assertions that we're in fact not doing so, and it fixes an oversight in the effect desugaring rework.

6 files changed, 85 insertions, 25 deletions

diff --git a/compiler/rustc_hir_analysis/src/bounds.rs b/compiler/rustc_hir_analysis/src/bounds.rs
index d0b0c08aa79..14ea7816291 100644
--- a/compiler/rustc_hir_analysis/src/bounds.rs
+++ b/compiler/rustc_hir_analysis/src/bounds.rs
@@ -9,6 +9,8 @@ use rustc_middle::ty::{self, Ty, TyCtxt, Upcast};
 use rustc_span::def_id::DefId;
 use rustc_span::Span;
 
+use crate::hir_ty_lowering::OnlySelfBounds;
+
 /// Collects together a list of type bounds. These lists of bounds occur in many places
 /// in Rust's syntax:
 ///
@@ -50,6 +52,7 @@ impl<'tcx> Bounds<'tcx> {
         span: Span,
         polarity: ty::PredicatePolarity,
         constness: ty::BoundConstness,
+        only_self_bounds: OnlySelfBounds,
     ) {
         let clause = (
             bound_trait_ref
@@ -66,7 +69,10 @@ impl<'tcx> Bounds<'tcx> {
             self.clauses.push(clause);
         }
 
-        if !tcx.features().effects {
+        // FIXME(effects): Lift this out of `push_trait_bound`, and move it somewhere else.
+        // Perhaps moving this into `lower_poly_trait_ref`, just like we lower associated
+        // type bounds.
+        if !tcx.features().effects || only_self_bounds.0 {
             return;
         }
         // For `T: ~const Tr` or `T: const Tr`, we need to add an additional bound on the
diff --git a/compiler/rustc_hir_analysis/src/collect/item_bounds.rs b/compiler/rustc_hir_analysis/src/collect/item_bounds.rs
index d62727e76b5..7a254c884c2 100644
--- a/compiler/rustc_hir_analysis/src/collect/item_bounds.rs
+++ b/compiler/rustc_hir_analysis/src/collect/item_bounds.rs
@@ -10,6 +10,7 @@ use rustc_span::Span;
 use rustc_type_ir::Upcast;
 use tracing::{debug, instrument};
 
+use super::predicates_of::assert_only_contains_predicates_from;
 use super::ItemCtxt;
 use crate::hir_ty_lowering::{HirTyLowerer, PredicateFilter};
 
@@ -56,6 +57,9 @@ fn associated_type_bounds<'tcx>(
         tcx.def_path_str(assoc_item_def_id.to_def_id()),
         all_bounds
     );
+
+    assert_only_contains_predicates_from(filter, all_bounds, item_ty);
+
     all_bounds
 }
 
@@ -108,18 +112,21 @@ pub(super) fn explicit_item_bounds_with_filter(
         Some(ty::ImplTraitInTraitData::Trait { opaque_def_id, .. }) => {
             let item = tcx.hir_node_by_def_id(opaque_def_id.expect_local()).expect_item();
             let opaque_ty = item.expect_opaque_ty();
-            return ty::EarlyBinder::bind(opaque_type_bounds(
+            let item_ty = Ty::new_projection_from_args(
+                tcx,
+                def_id.to_def_id(),
+                ty::GenericArgs::identity_for_item(tcx, def_id),
+            );
+            let bounds = opaque_type_bounds(
                 tcx,
                 opaque_def_id.expect_local(),
                 opaque_ty.bounds,
-                Ty::new_projection_from_args(
-                    tcx,
-                    def_id.to_def_id(),
-                    ty::GenericArgs::identity_for_item(tcx, def_id),
-                ),
+                item_ty,
                 item.span,
                 filter,
-            ));
+            );
+            assert_only_contains_predicates_from(filter, bounds, item_ty);
+            return ty::EarlyBinder::bind(bounds);
         }
         Some(ty::ImplTraitInTraitData::Impl { .. }) => span_bug!(
             tcx.def_span(def_id),
@@ -167,7 +174,9 @@ pub(super) fn explicit_item_bounds_with_filter(
         }) => {
             let args = GenericArgs::identity_for_item(tcx, def_id);
             let item_ty = Ty::new_opaque(tcx, def_id.to_def_id(), args);
-            opaque_type_bounds(tcx, def_id, bounds, item_ty, *span, filter)
+            let bounds = opaque_type_bounds(tcx, def_id, bounds, item_ty, *span, filter);
+            assert_only_contains_predicates_from(filter, bounds, item_ty);
+            bounds
         }
         // Since RPITITs are lowered as projections in `<dyn HirTyLowerer>::lower_ty`, when we're
         // asking for the item bounds of the *opaques* in a trait's default method signature, we
@@ -184,15 +193,18 @@ pub(super) fn explicit_item_bounds_with_filter(
             };
             let args = GenericArgs::identity_for_item(tcx, def_id);
             let item_ty = Ty::new_opaque(tcx, def_id.to_def_id(), args);
-            tcx.arena.alloc_slice(
+            let bounds = &*tcx.arena.alloc_slice(
                 &opaque_type_bounds(tcx, def_id, bounds, item_ty, *span, filter)
                     .to_vec()
                     .fold_with(&mut AssocTyToOpaque { tcx, fn_def_id: fn_def_id.to_def_id() }),
-            )
+            );
+            assert_only_contains_predicates_from(filter, bounds, item_ty);
+            bounds
         }
         hir::Node::Item(hir::Item { kind: hir::ItemKind::TyAlias(..), .. }) => &[],
         _ => bug!("item_bounds called on {:?}", def_id),
     };
+
     ty::EarlyBinder::bind(bounds)
 }
 
diff --git a/compiler/rustc_hir_analysis/src/collect/predicates_of.rs b/compiler/rustc_hir_analysis/src/collect/predicates_of.rs
index f9539ad0efb..67d8813d1f7 100644
--- a/compiler/rustc_hir_analysis/src/collect/predicates_of.rs
+++ b/compiler/rustc_hir_analysis/src/collect/predicates_of.rs
@@ -677,9 +677,63 @@ pub(super) fn implied_predicates_with_filter<'tcx>(
         _ => {}
     }
 
+    assert_only_contains_predicates_from(filter, implied_bounds, tcx.types.self_param);
+
     ty::EarlyBinder::bind(implied_bounds)
 }
 
+// Make sure when elaborating supertraits, probing for associated types, etc.,
+// we really truly are elaborating clauses that have `Self` as their self type.
+// This is very important since downstream code relies on this being correct.
+pub(super) fn assert_only_contains_predicates_from<'tcx>(
+    filter: PredicateFilter,
+    bounds: &'tcx [(ty::Clause<'tcx>, Span)],
+    ty: Ty<'tcx>,
+) {
+    if !cfg!(debug_assertions) {
+        return;
+    }
+
+    match filter {
+        PredicateFilter::SelfOnly | PredicateFilter::SelfThatDefines(_) => {
+            for (clause, _) in bounds {
+                match clause.kind().skip_binder() {
+                    ty::ClauseKind::Trait(trait_predicate) => {
+                        assert_eq!(
+                            trait_predicate.self_ty(),
+                            ty,
+                            "expected `Self` predicate when computing `{filter:?}` implied bounds: {clause:?}"
+                        );
+                    }
+                    ty::ClauseKind::Projection(projection_predicate) => {
+                        assert_eq!(
+                            projection_predicate.self_ty(),
+                            ty,
+                            "expected `Self` predicate when computing `{filter:?}` implied bounds: {clause:?}"
+                        );
+                    }
+                    ty::ClauseKind::TypeOutlives(outlives_predicate) => {
+                        assert_eq!(
+                            outlives_predicate.0, ty,
+                            "expected `Self` predicate when computing `{filter:?}` implied bounds: {clause:?}"
+                        );
+                    }
+
+                    ty::ClauseKind::RegionOutlives(_)
+                    | ty::ClauseKind::ConstArgHasType(_, _)
+                    | ty::ClauseKind::WellFormed(_)
+                    | ty::ClauseKind::ConstEvaluatable(_) => {
+                        bug!(
+                            "unexpected non-`Self` predicate when computing `{filter:?}` implied bounds: {clause:?}"
+                        );
+                    }
+                }
+            }
+        }
+        PredicateFilter::All | PredicateFilter::SelfAndAssociatedTypeBounds => {}
+    }
+}
+
 /// Returns the predicates defined on `item_def_id` of the form
 /// `X: Foo` where `X` is the type parameter `def_id`.
 #[instrument(level = "trace", skip(tcx))]
diff --git a/compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs b/compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs
index 4416caa71ff..35eebcb6be1 100644
--- a/compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs
+++ b/compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs
@@ -719,6 +719,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
             span,
             polarity,
             constness,
+            only_self_bounds,
         );
 
         let mut dup_constraints = FxIndexMap::default();
diff --git a/tests/ui/rfcs/rfc-2632-const-trait-impl/assoc-type.rs b/tests/ui/rfcs/rfc-2632-const-trait-impl/assoc-type.rs
index 348bf839b69..ea3cbabf302 100644
--- a/tests/ui/rfcs/rfc-2632-const-trait-impl/assoc-type.rs
+++ b/tests/ui/rfcs/rfc-2632-const-trait-impl/assoc-type.rs
@@ -39,7 +39,6 @@ impl const Foo for NonConstAdd {
 #[const_trait]
 trait Baz {
     type Qux: Add;
-    //~^ ERROR the trait bound
 }
 
 impl const Baz for NonConstAdd {
diff --git a/tests/ui/rfcs/rfc-2632-const-trait-impl/assoc-type.stderr b/tests/ui/rfcs/rfc-2632-const-trait-impl/assoc-type.stderr
index 405212b52c7..c20b53c210f 100644
--- a/tests/ui/rfcs/rfc-2632-const-trait-impl/assoc-type.stderr
+++ b/tests/ui/rfcs/rfc-2632-const-trait-impl/assoc-type.stderr
@@ -12,17 +12,5 @@ error: using `#![feature(effects)]` without enabling next trait solver globally
    = note: the next trait solver must be enabled globally for the effects feature to work correctly
    = help: use `-Znext-solver` to enable
 
-error[E0277]: the trait bound `Add::{synthetic#0}: Compat` is not satisfied
-  --> $DIR/assoc-type.rs:41:15
-   |
-LL |     type Qux: Add;
-   |               ^^^ the trait `Compat` is not implemented for `Add::{synthetic#0}`
-   |
-help: consider further restricting the associated type
-   |
-LL | trait Baz where Add::{synthetic#0}: Compat {
-   |           ++++++++++++++++++++++++++++++++
-
-error: aborting due to 2 previous errors; 1 warning emitted
+error: aborting due to 1 previous error; 1 warning emitted
 
-For more information about this error, try `rustc --explain E0277`.