Use DeepRejectCtxt in assemble_inherent_candidates_from_param

compiler/rustc_hir_typeck/src/lib.rs

@@ -2,6 +2,7 @@
 #![allow(rustc::diagnostic_outside_of_impl)]
 #![allow(rustc::untranslatable_diagnostic)]
 #![feature(array_windows)]
+#![feature(assert_matches)]
 #![feature(box_patterns)]
 #![feature(if_let_guard)]
 #![feature(iter_intersperse)]

compiler/rustc_hir_typeck/src/method/probe.rs

@@ -1,3 +1,4 @@
+use std::assert_matches::debug_assert_matches;
 use std::cell::{Cell, RefCell};
 use std::cmp::max;
 use std::ops::Deref;
@@ -16,7 +17,7 @@ use rustc_infer::traits::ObligationCauseCode;
 use rustc_middle::middle::stability;
 use rustc_middle::query::Providers;
 use rustc_middle::ty::elaborate::supertrait_def_ids;
-use rustc_middle::ty::fast_reject::{TreatParams, simplify_type};
+use rustc_middle::ty::fast_reject::{DeepRejectCtxt, TreatParams, simplify_type};
 use rustc_middle::ty::{
     self, AssocItem, AssocItemContainer, GenericArgs, GenericArgsRef, GenericParamDefKind,
     ParamEnvAnd, Ty, TyCtxt, TypeVisitableExt, Upcast,
@@ -807,8 +808,8 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
                     );
                 }
             }
-            ty::Param(p) => {
-                self.assemble_inherent_candidates_from_param(p);
+            ty::Param(_) => {
+                self.assemble_inherent_candidates_from_param(raw_self_ty);
             }
             ty::Bool
             | ty::Char
@@ -909,18 +910,16 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
     }
 
     #[instrument(level = "debug", skip(self))]
-    fn assemble_inherent_candidates_from_param(&mut self, param_ty: ty::ParamTy) {
+    fn assemble_inherent_candidates_from_param(&mut self, param_ty: Ty<'tcx>) {
+        debug_assert_matches!(param_ty.kind(), ty::Param(_));
+
+        let tcx = self.tcx;
         let bounds = self.param_env.caller_bounds().iter().filter_map(|predicate| {
             let bound_predicate = predicate.kind();
             match bound_predicate.skip_binder() {
-                ty::ClauseKind::Trait(trait_predicate) => {
-                    match *trait_predicate.trait_ref.self_ty().kind() {
-                        ty::Param(p) if p == param_ty => {
-                            Some(bound_predicate.rebind(trait_predicate.trait_ref))
-                        }
-                        _ => None,
-                    }
-                }
+                ty::ClauseKind::Trait(trait_predicate) => DeepRejectCtxt::relate_rigid_rigid(tcx)
+                    .types_may_unify(param_ty, trait_predicate.trait_ref.self_ty())
+                    .then(|| bound_predicate.rebind(trait_predicate.trait_ref)),
                 ty::ClauseKind::RegionOutlives(_)
                 | ty::ClauseKind::TypeOutlives(_)
                 | ty::ClauseKind::Projection(_)

tests/ui/traits/next-solver/method/param-method-from-unnormalized-param-env-2.rs

@@ -0,0 +1,29 @@
+//@ check-pass
+//@ revisions: current next
+//@ ignore-compare-mode-next-solver (explicit revisions)
+//@[next] compile-flags: -Znext-solver
+
+// Regression test for <https://github.com/rust-lang/trait-system-refactor-initiative/issues/214>.
+// See comment below.
+
+trait A {
+    fn hello(&self) {}
+}
+
+trait B {
+    fn hello(&self) {}
+}
+
+impl<T> A for T {}
+impl<T> B for T {}
+
+fn test<F, R>(q: F::Item)
+where
+    F: Iterator<Item = R>,
+    // We want to prefer `A` for `R.hello()`
+    F::Item: A,
+{
+    q.hello();
+}
+
+fn main() {}

tests/ui/traits/next-solver/method/param-method-from-unnormalized-param-env.rs

@@ -0,0 +1,17 @@
+//@ check-pass
+//@ compile-flags: -Znext-solver
+
+// Regression test for <https://github.com/rust-lang/trait-system-refactor-initiative/issues/214>.
+
+fn execute<K, F, R>(q: F::Item) -> R
+where
+    F: Iterator<Item = R>,
+    // Both of the below bounds should be considered for `.into()`, and then be combined
+    // into a single `R: Into<?0>` bound which can be inferred to `?0 = R`.
+    F::Item: Into<K>,
+    R: Into<String>,
+{
+    q.into()
+}
+
+fn main() {}