Add to_constraint_category to ObligationCause and SubregionOrigin

compiler/rustc_middle/src/traits/mod.rs

@@ -10,6 +10,7 @@ mod structural_impls;
 pub mod util;
 
 use crate::infer::canonical::Canonical;
+use crate::mir::ConstraintCategory;
 use crate::ty::abstract_const::NotConstEvaluatable;
 use crate::ty::subst::SubstsRef;
 use crate::ty::{self, AdtKind, Ty, TyCtxt};
@@ -183,6 +184,13 @@ impl<'tcx> ObligationCause<'tcx> {
             variant(DerivedObligationCause { parent_trait_pred, parent_code: self.code }).into();
         self
     }
+
+    pub fn to_constraint_category(&self) -> ConstraintCategory<'tcx> {
+        match self.code() {
+            MatchImpl(cause, _) => cause.to_constraint_category(),
+            _ => ConstraintCategory::BoringNoLocation,
+        }
+    }
 }
 
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Lift)]