Add a test for #2021

tests/source/match.rs

@@ -425,3 +425,12 @@ fn issue_2099() {
 
     match x {}
 }
+
+// #2021
+impl<'tcx> Const<'tcx> {
+    pub fn from_constval<'a>() -> Const<'tcx> {
+        let val = match *cv {
+            ConstVal::Variant(_) | ConstVal::Aggregate(..) | ConstVal::Unevaluated(..) => bug!("MIR must not use `{:?}` (aggregates are expanded to MIR rvalues)", cv),
+        };
+    }
+}

tests/target/match.rs

@@ -463,3 +463,15 @@ fn issue_2099() {
 
     match x {}
 }
+
+// #2021
+impl<'tcx> Const<'tcx> {
+    pub fn from_constval<'a>() -> Const<'tcx> {
+        let val = match *cv {
+            ConstVal::Variant(_) | ConstVal::Aggregate(..) | ConstVal::Unevaluated(..) => bug!(
+                "MIR must not use `{:?}` (aggregates are expanded to MIR rvalues)",
+                cv
+            ),
+        };
+    }
+}