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

compiler/rustc_hir_analysis/src/astconv/mod.rs

@@ -26,12 +26,12 @@
 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::{InferCtxt, InferOk, TyCtxtInferExt};
+use rustc_infer::infer::{InferCtxt, TyCtxtInferExt};
-use rustc_infer::traits::{Obligation, ObligationCause};
+use rustc_infer::traits::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,
+    self, Const, GenericArgKind, GenericArgsRef, IsSuggestable, ParamEnv, Ty, TyCtxt,
     TypeVisitableExt,
 };
 use rustc_session::lint::builtin::AMBIGUOUS_ASSOCIATED_ITEMS;
@@ -40,7 +40,7 @@
 use rustc_span::{sym, BytePos, Span, DUMMY_SP};
 use rustc_target::spec::abi;
 use rustc_trait_selection::traits::wf::object_region_bounds;
-use rustc_trait_selection::traits::{self, NormalizeExt, ObligationCtxt};
+use rustc_trait_selection::traits::{self, ObligationCtxt};
 
 use std::fmt::Display;
 use std::slice;
@@ -1606,7 +1606,6 @@ fn lookup_inherent_assoc_ty(
         // FIXME(inherent_associated_types): Acquiring the ParamEnv this early leads to cycle errors
         // when inside of an ADT (#108491) or where clause.
         let param_env = tcx.param_env(block.owner);
-        let cause = ObligationCause::misc(span, block.owner.def_id);
 
         let mut universes = if self_ty.has_escaping_bound_vars() {
             vec![None; self_ty.outer_exclusive_binder().as_usize()]
@@ -1614,24 +1613,16 @@ fn lookup_inherent_assoc_ty(
             vec![]
         };
 
+        let (impl_, (assoc_item, def_scope)) =
             crate::traits::project::with_replaced_escaping_bound_vars(
                 infcx,
                 &mut universes,
                 self_ty,
                 |self_ty| {
-                let tcx = self.tcx();
+                    self.select_inherent_assoc_type_candidates(
-                let InferOk { value: self_ty, obligations } =
+                        infcx, name, span, self_ty, param_env, candidates,
-                    infcx.at(&cause, param_env).normalize(self_ty);
+                    )
-
+                },
-                let (impl_, (assoc_item, def_scope)) = self.select_inherent_assoc_type_candidates(
-                    infcx,
-                    name,
-                    span,
-                    self_ty,
-                    cause,
-                    param_env,
-                    obligations,
-                    candidates,
             )?;
 
         self.check_assoc_ty(assoc_item, name, def_scope, block, span);
@@ -1640,8 +1631,7 @@ fn lookup_inherent_assoc_ty(
         // `create_args_for_associated_item`. Modify the latter instead (or sth. similar) to
         // not require the parent args logic.
         let parent_args = ty::GenericArgs::identity_for_item(tcx, impl_);
-                let args =
+        let args = self.create_args_for_associated_item(span, assoc_item, segment, parent_args);
-                    self.create_args_for_associated_item(span, assoc_item, segment, parent_args);
         let args = tcx.mk_args_from_iter(
             std::iter::once(ty::GenericArg::from(self_ty))
                 .chain(args.into_iter().skip(parent_args.len())),
@@ -1650,8 +1640,6 @@ fn lookup_inherent_assoc_ty(
         let ty = Ty::new_alias(tcx, ty::Inherent, ty::AliasTy::new(tcx, assoc_item, args));
 
         Ok(Some((ty, assoc_item)))
-            },
-        )
     }
 
     fn select_inherent_assoc_type_candidates(
@@ -1660,9 +1648,7 @@ fn select_inherent_assoc_type_candidates(
         name: Ident,
         span: Span,
         self_ty: Ty<'tcx>,
-        cause: ObligationCause<'tcx>,
         param_env: ParamEnv<'tcx>,
-        obligations: Vec<Obligation<'tcx, Predicate<'tcx>>>,
         candidates: Vec<(DefId, (DefId, DefId))>,
     ) -> Result<(DefId, (DefId, DefId)), ErrorGuaranteed> {
         let tcx = self.tcx();
@@ -1674,11 +1660,11 @@ fn select_inherent_assoc_type_candidates(
             .filter(|&(impl_, _)| {
                 infcx.probe(|_| {
                     let ocx = ObligationCtxt::new(infcx);
-                    ocx.register_obligations(obligations.clone());
+                    let self_ty = ocx.normalize(&ObligationCause::dummy(), param_env, self_ty);
 
                     let impl_args = infcx.fresh_args_for_item(span, impl_);
                     let impl_ty = tcx.type_of(impl_).instantiate(tcx, impl_args);
-                    let impl_ty = ocx.normalize(&cause, param_env, impl_ty);
+                    let impl_ty = ocx.normalize(&ObligationCause::dummy(), param_env, impl_ty);
 
                     // Check that the self types can be related.
                     if ocx.eq(&ObligationCause::dummy(), param_env, impl_ty, self_ty).is_err() {
@@ -1687,9 +1673,10 @@ fn select_inherent_assoc_type_candidates(
 
                     // Check whether the impl imposes obligations we have to worry about.
                     let impl_bounds = tcx.predicates_of(impl_).instantiate(tcx, impl_args);
-                    let impl_bounds = ocx.normalize(&cause, param_env, impl_bounds);
+                    let impl_bounds =
+                        ocx.normalize(&ObligationCause::dummy(), param_env, impl_bounds);
                     let impl_obligations = traits::predicates_for_generics(
-                        |_, _| cause.clone(),
+                        |_, _| ObligationCause::dummy(),
                         param_env,
                         impl_bounds,
                     );

compiler/rustc_trait_selection/src/traits/project.rs

@@ -1454,7 +1454,18 @@ pub fn compute_inherent_assoc_ty_args<'a, 'b, 'tcx>(
 
     // Infer the generic parameters of the impl by unifying the
     // impl type with the self type of the projection.
-    let self_ty = alias_ty.self_ty();
+    let mut self_ty = alias_ty.self_ty();
+    if !selcx.infcx.next_trait_solver() {
+        self_ty = normalize_with_depth_to(
+            selcx,
+            param_env,
+            cause.clone(),
+            depth + 1,
+            self_ty,
+            obligations,
+        );
+    }
+
     match selcx.infcx.at(&cause, param_env).eq(DefineOpaqueTypes::No, impl_ty, self_ty) {
         Ok(mut ok) => obligations.append(&mut ok.obligations),
         Err(_) => {

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() {}