From 7bca516b357f5cf596250f99353a08f65cb0456a Mon Sep 17 00:00:00 2001
From: Michael Goulet <michael@errs.io>
Date: Mon, 22 Jul 2024 13:54:48 -0400
Subject: [PATCH] Get rid of can_eq_shallow

---
 compiler/rustc_infer/src/infer/mod.rs                | 12 ------------
 .../src/error_reporting/infer/note_and_explain.rs    |  5 +++--
 2 files changed, 3 insertions(+), 14 deletions(-)

diff --git a/compiler/rustc_infer/src/infer/mod.rs b/compiler/rustc_infer/src/infer/mod.rs
index 7fc4e36d75274..3cee0a622f17b 100644
--- a/compiler/rustc_infer/src/infer/mod.rs
+++ b/compiler/rustc_infer/src/infer/mod.rs
@@ -755,18 +755,6 @@ impl<'tcx> InferCtxt<'tcx> {
             .collect()
     }
 
-    // FIXME(-Znext-solver): Get rid of this method, it's never correct. Either that,
-    // or we need to process the obligations.
-    pub fn can_eq_shallow<T>(&self, param_env: ty::ParamEnv<'tcx>, a: T, b: T) -> bool
-    where
-        T: at::ToTrace<'tcx>,
-    {
-        let origin = &ObligationCause::dummy();
-        // We're only answering whether the types could be the same, and with
-        // opaque types, "they can be the same", via registering a hidden type.
-        self.probe(|_| self.at(origin, param_env).eq(DefineOpaqueTypes::Yes, a, b).is_ok())
-    }
-
     #[instrument(skip(self), level = "debug")]
     pub fn sub_regions(
         &self,
diff --git a/compiler/rustc_trait_selection/src/error_reporting/infer/note_and_explain.rs b/compiler/rustc_trait_selection/src/error_reporting/infer/note_and_explain.rs
index 1ff2fca83faf2..f9110cfb3b970 100644
--- a/compiler/rustc_trait_selection/src/error_reporting/infer/note_and_explain.rs
+++ b/compiler/rustc_trait_selection/src/error_reporting/infer/note_and_explain.rs
@@ -12,6 +12,7 @@ use rustc_middle::{
 use rustc_span::{def_id::DefId, sym, BytePos, Span, Symbol};
 
 use crate::error_reporting::TypeErrCtxt;
+use crate::infer::InferCtxtExt;
 
 impl<'tcx> TypeErrCtxt<'_, 'tcx> {
     pub fn note_and_explain_type_err(
@@ -821,7 +822,7 @@ fn foo(&self) -> Self::T { String::new() }
                                 tcx.defaultness(item.id.owner_id)
                             {
                                 let assoc_ty = tcx.type_of(item.id.owner_id).instantiate_identity();
-                                if self.infcx.can_eq_shallow(param_env, assoc_ty, found) {
+                                if self.infcx.can_eq(param_env, assoc_ty, found) {
                                     diag.span_label(
                                         item.span,
                                         "associated type defaults can't be assumed inside the \
@@ -844,7 +845,7 @@ fn foo(&self) -> Self::T { String::new() }
                         let assoc_ty = tcx.type_of(item.id.owner_id).instantiate_identity();
                         if let hir::Defaultness::Default { has_value: true } =
                             tcx.defaultness(item.id.owner_id)
-                            && self.infcx.can_eq_shallow(param_env, assoc_ty, found)
+                            && self.infcx.can_eq(param_env, assoc_ty, found)
                         {
                             diag.span_label(
                                 item.span,