Get rid of infer vars in inherent assoc types selection by using EagerResolver folder

Author: spastorino

compiler/rustc_hir_analysis/src/astconv/mod.rs

@@ -26,13 +26,14 @@ use rustc_hir::def::{CtorOf, DefKind, Namespace, Res};
 use rustc_hir::def_id::{DefId, LocalDefId};
 use rustc_hir::intravisit::{walk_generics, Visitor as _};
 use rustc_hir::{GenericArg, GenericArgs, OpaqueTyOrigin};
+use rustc_infer::infer::resolve::EagerResolver;
 use rustc_infer::infer::{InferCtxt, InferOk, TyCtxtInferExt};
 use rustc_infer::traits::{Obligation, ObligationCause};
 use rustc_middle::middle::stability::AllowUnstable;
 use rustc_middle::ty::GenericParamDefKind;
 use rustc_middle::ty::{
     self, Const, GenericArgKind, GenericArgsRef, IsSuggestable, ParamEnv, Predicate, Ty, TyCtxt,
-    TypeVisitableExt,
+    TypeFoldable, TypeVisitableExt,
 };
 use rustc_session::lint::builtin::AMBIGUOUS_ASSOCIATED_ITEMS;
 use rustc_span::edit_distance::find_best_match_for_name;
@@ -1648,6 +1649,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                 );
 
                 let ty = Ty::new_alias(tcx, ty::Inherent, ty::AliasTy::new(tcx, assoc_item, args));
+                let ty = ty.fold_with(&mut EagerResolver::new(infcx));
 
                 Ok(Some((ty, assoc_item)))
             },

compiler/rustc_trait_selection/src/solve/eval_ctxt/mod.rs

@@ -33,7 +33,7 @@ use super::{search_graph, GoalEvaluationKind};
 use super::{search_graph::SearchGraph, Goal};
 pub use select::InferCtxtSelectExt;
 
-mod canonical;
+pub mod canonical;
 mod commit_if_ok;
 mod probe;
 mod select;

compiler/rustc_trait_selection/src/solve/mod.rs

@@ -31,7 +31,7 @@ use rustc_middle::ty::{
 mod alias_relate;
 mod assembly;
 mod canonicalize;
-mod eval_ctxt;
+pub mod eval_ctxt;
 mod fulfill;
 pub mod inspect;
 mod normalize;

tests/ui/associated-inherent-types/assoc-inherent-late-bound.rs

@@ -0,0 +1,14 @@
+// check-pass
+
+#![feature(inherent_associated_types)]
+#![allow(incomplete_features)]
+
+struct Foo<T>(T);
+
+impl<'a> Foo<fn(&'a ())> {
+    type Assoc = &'a ();
+}
+
+fn bar(_: for<'a> fn(Foo<fn(Foo<fn(&'static ())>::Assoc)>::Assoc)) {}
+
+fn main() {}