From a0b83f542f91699838c65d772b0eb6aeb276fb67 Mon Sep 17 00:00:00 2001
From: Deadbeef <ent3rm4n@gmail.com>
Date: Sat, 11 Sep 2021 09:40:19 +0000
Subject: [PATCH] Fix duplicate bounds for const_trait_impl

---
 .../rustc_trait_selection/src/traits/select/mod.rs  |  5 +++--
 .../call-generic-method-dup-bound.rs                | 13 +++++++++----
 2 files changed, 12 insertions(+), 6 deletions(-)

diff --git a/compiler/rustc_trait_selection/src/traits/select/mod.rs b/compiler/rustc_trait_selection/src/traits/select/mod.rs
index 22013fb79cf..3c83938ce43 100644
--- a/compiler/rustc_trait_selection/src/traits/select/mod.rs
+++ b/compiler/rustc_trait_selection/src/traits/select/mod.rs
@@ -1487,10 +1487,11 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             ) => false,
 
             (ParamCandidate(other), ParamCandidate(victim)) => {
-                let value_same_except_bound_vars = other.value.skip_binder()
+                let same_except_bound_vars = other.value.skip_binder()
                     == victim.value.skip_binder()
+                    && other.constness == victim.constness
                     && !other.value.skip_binder().has_escaping_bound_vars();
-                if value_same_except_bound_vars {
+                if same_except_bound_vars {
                     // See issue #84398. In short, we can generate multiple ParamCandidates which are
                     // the same except for unused bound vars. Just pick the one with the fewest bound vars
                     // or the current one if tied (they should both evaluate to the same answer). This is
diff --git a/src/test/ui/rfc-2632-const-trait-impl/call-generic-method-dup-bound.rs b/src/test/ui/rfc-2632-const-trait-impl/call-generic-method-dup-bound.rs
index 7185376b440..cc24dbd96d2 100644
--- a/src/test/ui/rfc-2632-const-trait-impl/call-generic-method-dup-bound.rs
+++ b/src/test/ui/rfc-2632-const-trait-impl/call-generic-method-dup-bound.rs
@@ -16,12 +16,17 @@ impl const PartialEq for S {
 
 // This duplicate bound should not result in ambiguities. It should be equivalent to a single ~const
 // bound.
-// const fn equals_self<T: PartialEq + ~const PartialEq>(t: &T) -> bool {
-// FIXME(fee1-dead)^ why should the order matter here?
-const fn equals_self<T: ~const PartialEq + PartialEq>(t: &T) -> bool {
+const fn equals_self<T: PartialEq + ~const PartialEq>(t: &T) -> bool {
     *t == *t
 }
 
-pub const EQ: bool = equals_self(&S);
+trait A: PartialEq {}
+impl<T: PartialEq> A for T {}
+
+const fn equals_self2<T: A + ~const PartialEq>(t: &T) -> bool {
+    *t == *t
+}
+
+pub const EQ: bool = equals_self(&S) && equals_self2(&S);
 
 fn main() {}