Revert "Rollup merge of #92006 - oli-obk:welcome_opaque_types_into_th…

…e_fold, r=nikomatsakis" This reverts commit b45a819, reversing changes made to e045c79.
rust-lang · Jan 15, 2022 · fd04250 · fd04250
1 parent 38c22af
commit fd04250
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Showing 4 changed files with 80 additions and 61 deletions.
diff --git a/compiler/rustc_infer/src/infer/opaque_types.rs b/compiler/rustc_infer/src/infer/opaque_types.rs
@@ -555,22 +555,6 @@ impl<'a, 'tcx> Instantiator<'a, 'tcx> {
             let predicate = predicate.subst(tcx, substs);
             debug!(?predicate);
 
-            let predicate = predicate.fold_with(&mut BottomUpFolder {
-                tcx,
-                ty_op: |ty| match *ty.kind() {
-                    // Replace all other mentions of the same opaque type with the hidden type,
-                    // as the bounds must hold on the hidden type after all.
-                    ty::Opaque(def_id2, substs2) if def_id == def_id2 && substs == substs2 => {
-                        ty_var
-                    }
-                    // Instantiate nested instances of `impl Trait`.
-                    ty::Opaque(..) => self.instantiate_opaque_types_in_map(ty),
-                    _ => ty,
-                },
-                lt_op: |lt| lt,
-                ct_op: |ct| ct,
-            });
-
             // We can't normalize associated types from `rustc_infer`, but we can eagerly register inference variables for them.
             let predicate = predicate.fold_with(&mut BottomUpFolder {
                 tcx,
@@ -595,6 +579,10 @@ impl<'a, 'tcx> Instantiator<'a, 'tcx> {
                     return tcx.ty_error();
                 }
             }
+            // Change the predicate to refer to the type variable,
+            // which will be the concrete type instead of the opaque type.
+            // This also instantiates nested instances of `impl Trait`.
+            let predicate = self.instantiate_opaque_types_in_map(predicate);
 
             let cause =
                 traits::ObligationCause::new(self.value_span, self.body_id, traits::OpaqueType);

diff --git a/compiler/rustc_trait_selection/src/traits/query/type_op/mod.rs b/compiler/rustc_trait_selection/src/traits/query/type_op/mod.rs
@@ -4,9 +4,7 @@ use crate::infer::canonical::{
 use crate::infer::{InferCtxt, InferOk};
 use crate::traits::query::Fallible;
 use crate::traits::ObligationCause;
-use rustc_infer::infer::canonical::{Canonical, Certainty};
-use rustc_infer::traits::query::NoSolution;
-use rustc_infer::traits::PredicateObligations;
+use rustc_infer::infer::canonical::Canonical;
 use rustc_middle::ty::fold::TypeFoldable;
 use rustc_middle::ty::{ParamEnvAnd, TyCtxt};
 use std::fmt;
@@ -19,6 +17,7 @@ pub mod implied_outlives_bounds;
 pub mod normalize;
 pub mod outlives;
 pub mod prove_predicate;
+use self::prove_predicate::ProvePredicate;
 pub mod subtype;
 
 pub use rustc_middle::traits::query::type_op::*;
@@ -81,14 +80,9 @@ pub trait QueryTypeOp<'tcx>: fmt::Debug + Copy + TypeFoldable<'tcx> + 'tcx {
         query_key: ParamEnvAnd<'tcx, Self>,
         infcx: &InferCtxt<'_, 'tcx>,
         output_query_region_constraints: &mut QueryRegionConstraints<'tcx>,
-    ) -> Fallible<(
-        Self::QueryResponse,
-        Option<Canonical<'tcx, ParamEnvAnd<'tcx, Self>>>,
-        PredicateObligations<'tcx>,
-        Certainty,
-    )> {
+    ) -> Fallible<(Self::QueryResponse, Option<Canonical<'tcx, ParamEnvAnd<'tcx, Self>>>)> {
         if let Some(result) = QueryTypeOp::try_fast_path(infcx.tcx, &query_key) {
-            return Ok((result, None, vec![], Certainty::Proven));
+            return Ok((result, None));
         }
 
         // FIXME(#33684) -- We need to use
@@ -110,7 +104,20 @@ pub trait QueryTypeOp<'tcx>: fmt::Debug + Copy + TypeFoldable<'tcx> + 'tcx {
                 output_query_region_constraints,
             )?;
 
-        Ok((value, Some(canonical_self), obligations, canonical_result.value.certainty))
+        // Typically, instantiating NLL query results does not
+        // create obligations. However, in some cases there
+        // are unresolved type variables, and unify them *can*
+        // create obligations. In that case, we have to go
+        // fulfill them. We do this via a (recursive) query.
+        for obligation in obligations {
+            let ((), _) = ProvePredicate::fully_perform_into(
+                obligation.param_env.and(ProvePredicate::new(obligation.predicate)),
+                infcx,
+                output_query_region_constraints,
+            )?;
+        }
+
+        Ok((value, Some(canonical_self)))
     }
 }
 
@@ -122,39 +129,9 @@ where
 
     fn fully_perform(self, infcx: &InferCtxt<'_, 'tcx>) -> Fallible<TypeOpOutput<'tcx, Self>> {
         let mut region_constraints = QueryRegionConstraints::default();
-        let (output, canonicalized_query, mut obligations, _) =
+        let (output, canonicalized_query) =
             Q::fully_perform_into(self, infcx, &mut region_constraints)?;
 
-        // Typically, instantiating NLL query results does not
-        // create obligations. However, in some cases there
-        // are unresolved type variables, and unify them *can*
-        // create obligations. In that case, we have to go
-        // fulfill them. We do this via a (recursive) query.
-        while !obligations.is_empty() {
-            trace!("{:#?}", obligations);
-            let mut progress = false;
-            for obligation in std::mem::take(&mut obligations) {
-                let obligation = infcx.resolve_vars_if_possible(obligation);
-                match ProvePredicate::fully_perform_into(
-                    obligation.param_env.and(ProvePredicate::new(obligation.predicate)),
-                    infcx,
-                    &mut region_constraints,
-                ) {
-                    Ok(((), _, new, certainty)) => {
-                        obligations.extend(new);
-                        progress = true;
-                        if let Certainty::Ambiguous = certainty {
-                            obligations.push(obligation);
-                        }
-                    }
-                    Err(_) => obligations.push(obligation),
-                }
-            }
-            if !progress {
-                return Err(NoSolution);
-            }
-        }
-
         // Promote the final query-region-constraints into a
         // (optional) ref-counted vector:
         let region_constraints =

diff --git a/src/test/ui/type-alias-impl-trait/bound_reduction2.rs b/src/test/ui/type-alias-impl-trait/bound_reduction2.rs
@@ -15,5 +15,9 @@ impl<W> Trait<W> for () {}
 
 fn foo_desugared<T: TraitWithAssoc>(_: T) -> Foo<T::Assoc> {
     //~^ ERROR non-defining opaque type use in defining scope
+    //~| ERROR non-defining opaque type use in defining scope
+    //~| ERROR non-defining opaque type use in defining scope
+    //~| ERROR `T` is part of concrete type but not used in parameter list
+    //~| ERROR `T` is part of concrete type but not used in parameter list
     ()
 }
diff --git a/src/test/ui/type-alias-impl-trait/bound_reduction2.stderr b/src/test/ui/type-alias-impl-trait/bound_reduction2.stderr
@@ -1,20 +1,70 @@
+error: type parameter `T` is part of concrete type but not used in parameter list for the `impl Trait` type alias
+  --> $DIR/bound_reduction2.rs:16:60
+   |
+LL |   fn foo_desugared<T: TraitWithAssoc>(_: T) -> Foo<T::Assoc> {
+   |  ____________________________________________________________^
+LL | |
+LL | |
+LL | |
+...  |
+LL | |     ()
+LL | | }
+   | |_^
+
+error: type parameter `T` is part of concrete type but not used in parameter list for the `impl Trait` type alias
+  --> $DIR/bound_reduction2.rs:16:60
+   |
+LL |   fn foo_desugared<T: TraitWithAssoc>(_: T) -> Foo<T::Assoc> {
+   |  ____________________________________________________________^
+LL | |
+LL | |
+LL | |
+...  |
+LL | |     ()
+LL | | }
+   | |_^
+
 error: non-defining opaque type use in defining scope
-  --> $DIR/bound_reduction2.rs:16:46
+  --> $DIR/bound_reduction2.rs:16:1
    |
 LL | fn foo_desugared<T: TraitWithAssoc>(_: T) -> Foo<T::Assoc> {
-   |                                              ^^^^^^^^^^^^^
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
 note: used non-generic type `<T as TraitWithAssoc>::Assoc` for generic parameter
   --> $DIR/bound_reduction2.rs:9:10
    |
 LL | type Foo<V> = impl Trait<V>;
    |          ^
 
+error: non-defining opaque type use in defining scope
+  --> $DIR/bound_reduction2.rs:16:1
+   |
+LL | fn foo_desugared<T: TraitWithAssoc>(_: T) -> Foo<T::Assoc> {
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+note: used non-generic type `_` for generic parameter
+  --> $DIR/bound_reduction2.rs:9:10
+   |
+LL | type Foo<V> = impl Trait<V>;
+   |          ^
+
+error: non-defining opaque type use in defining scope
+  --> $DIR/bound_reduction2.rs:16:1
+   |
+LL | fn foo_desugared<T: TraitWithAssoc>(_: T) -> Foo<T::Assoc> {
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+note: used non-generic type `_` for generic parameter
+  --> $DIR/bound_reduction2.rs:9:10
+   |
+LL | type Foo<V> = impl Trait<V>;
+   |          ^
+
 error: could not find defining uses
   --> $DIR/bound_reduction2.rs:9:15
    |
 LL | type Foo<V> = impl Trait<V>;
    |               ^^^^^^^^^^^^^
 
-error: aborting due to 2 previous errors
+error: aborting due to 6 previous errors