From 760673e97d48e131b87ec738cb7106c5f8abe55e Mon Sep 17 00:00:00 2001
From: Michael Goulet <michael@errs.io>
Date: Mon, 8 Jan 2024 01:07:14 +0000
Subject: [PATCH] Remove logic in one_bound in astconv that prefers non-const
 bounds

---
 .../rustc_hir_analysis/src/astconv/mod.rs     | 35 ++-----------------
 .../const-impl-trait.rs                       |  2 ++
 .../const-impl-trait.stderr                   | 21 +++++------
 3 files changed, 13 insertions(+), 45 deletions(-)

diff --git a/compiler/rustc_hir_analysis/src/astconv/mod.rs b/compiler/rustc_hir_analysis/src/astconv/mod.rs
index 092df257dbfae..70f0c9bc4325b 100644
--- a/compiler/rustc_hir_analysis/src/astconv/mod.rs
+++ b/compiler/rustc_hir_analysis/src/astconv/mod.rs
@@ -1032,7 +1032,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
             self.trait_defines_associated_item_named(r.def_id(), assoc_kind, assoc_name)
         });
 
-        let Some(mut bound) = matching_candidates.next() else {
+        let Some(bound) = matching_candidates.next() else {
             let reported = self.complain_about_assoc_item_not_found(
                 all_candidates,
                 &ty_param_name.to_string(),
@@ -1046,38 +1046,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
         };
         debug!(?bound);
 
-        // look for a candidate that is not the same as our first bound, disregarding
-        // whether the bound is const.
-        let mut next_cand = matching_candidates.next();
-        while let Some(mut bound2) = next_cand {
-            debug!(?bound2);
-            if bound2.bound_vars() != bound.bound_vars() {
-                break;
-            }
-
-            let generics = tcx.generics_of(bound.def_id());
-            let Some(host_index) = generics.host_effect_index else { break };
-
-            // always return the bound that contains the host param.
-            if let ty::ConstKind::Param(_) = bound2.skip_binder().args.const_at(host_index).kind() {
-                (bound, bound2) = (bound2, bound);
-            }
-
-            let unconsted_args = bound
-                .skip_binder()
-                .args
-                .iter()
-                .enumerate()
-                .map(|(n, arg)| if host_index == n { tcx.consts.true_.into() } else { arg });
-
-            if unconsted_args.eq(bound2.skip_binder().args.iter()) {
-                next_cand = matching_candidates.next();
-            } else {
-                break;
-            }
-        }
-
-        if let Some(bound2) = next_cand {
+        if let Some(bound2) = matching_candidates.next() {
             debug!(?bound2);
 
             let assoc_kind_str = assoc_kind_str(assoc_kind);
diff --git a/tests/ui/rfcs/rfc-2632-const-trait-impl/const-impl-trait.rs b/tests/ui/rfcs/rfc-2632-const-trait-impl/const-impl-trait.rs
index 14d306fc31f6b..9d579e67a4be4 100644
--- a/tests/ui/rfcs/rfc-2632-const-trait-impl/const-impl-trait.rs
+++ b/tests/ui/rfcs/rfc-2632-const-trait-impl/const-impl-trait.rs
@@ -1,4 +1,6 @@
 // known-bug: #110395
+// Broken until we have `&T: const Deref` impl in stdlib
+
 #![allow(incomplete_features)]
 #![feature(
     associated_type_bounds,
diff --git a/tests/ui/rfcs/rfc-2632-const-trait-impl/const-impl-trait.stderr b/tests/ui/rfcs/rfc-2632-const-trait-impl/const-impl-trait.stderr
index d0ca1b19ad17d..d4be71f2f4661 100644
--- a/tests/ui/rfcs/rfc-2632-const-trait-impl/const-impl-trait.stderr
+++ b/tests/ui/rfcs/rfc-2632-const-trait-impl/const-impl-trait.stderr
@@ -1,5 +1,5 @@
 error[E0277]: can't compare `()` with `()`
-  --> $DIR/const-impl-trait.rs:35:17
+  --> $DIR/const-impl-trait.rs:37:17
    |
 LL |     assert!(cmp(&()));
    |             --- ^^^ no implementation for `() == ()`
@@ -9,23 +9,20 @@ LL |     assert!(cmp(&()));
    = help: the trait `const PartialEq` is not implemented for `()`
    = help: the trait `PartialEq` is implemented for `()`
 note: required by a bound in `cmp`
-  --> $DIR/const-impl-trait.rs:12:23
+  --> $DIR/const-impl-trait.rs:14:23
    |
 LL | const fn cmp(a: &impl ~const PartialEq) -> bool {
    |                       ^^^^^^^^^^^^^^^^ required by this bound in `cmp`
 
-error[E0277]: can't compare `&impl ~const PartialEq` with `&impl ~const PartialEq`
-  --> $DIR/const-impl-trait.rs:13:7
+error[E0369]: binary operation `==` cannot be applied to type `&impl ~const PartialEq`
+  --> $DIR/const-impl-trait.rs:15:7
    |
 LL |     a == a
-   |       ^^ no implementation for `&impl ~const PartialEq == &impl ~const PartialEq`
-   |
-   = help: the trait `~const PartialEq<&impl ~const PartialEq>` is not implemented for `&impl ~const PartialEq`
-help: consider dereferencing both sides of the expression
-   |
-LL |     *a == *a
-   |     +     +
+   |     - ^^ - &impl ~const PartialEq
+   |     |
+   |     &impl ~const PartialEq
 
 error: aborting due to 2 previous errors
 
-For more information about this error, try `rustc --explain E0277`.
+Some errors have detailed explanations: E0277, E0369.
+For more information about an error, try `rustc --explain E0277`.