Make root vars more stable

2 files changed, 6 insertions, 0 deletions

diff --git a/compiler/rustc_infer/src/infer/type_variable.rs b/compiler/rustc_infer/src/infer/type_variable.rs
index 2086483b94a..6f6791804d3 100644
--- a/compiler/rustc_infer/src/infer/type_variable.rs
+++ b/compiler/rustc_infer/src/infer/type_variable.rs
@@ -238,6 +238,9 @@ impl<'tcx> ut::UnifyKey for TyVidEqKey<'tcx> {
     fn tag() -> &'static str {
         "TyVidEqKey"
     }
+    fn order_roots(a: Self, _: &Self::Value, b: Self, _: &Self::Value) -> Option<(Self, Self)> {
+        if a.vid.as_u32() < b.vid.as_u32() { Some((a, b)) } else { Some((b, a)) }
+    }
 }
 
 impl<'tcx> ut::UnifyValue for TypeVariableValue<'tcx> {
diff --git a/compiler/rustc_infer/src/infer/unify_key.rs b/compiler/rustc_infer/src/infer/unify_key.rs
index 3ba8aea1d3a..5e5d0e063a0 100644
--- a/compiler/rustc_infer/src/infer/unify_key.rs
+++ b/compiler/rustc_infer/src/infer/unify_key.rs
@@ -137,6 +137,9 @@ impl<'tcx> UnifyKey for ConstVidKey<'tcx> {
     fn tag() -> &'static str {
         "ConstVidKey"
     }
+    fn order_roots(a: Self, _: &Self::Value, b: Self, _: &Self::Value) -> Option<(Self, Self)> {
+        if a.vid.as_u32() < b.vid.as_u32() { Some((a, b)) } else { Some((b, a)) }
+    }
 }
 
 impl<'tcx> UnifyValue for ConstVariableValue<'tcx> {