1 files changed, 45 insertions, 0 deletions
diff --git a/compiler/rustc_query_impl/src/values.rs b/compiler/rustc_query_impl/src/values.rs
new file mode 100644
index 000000000..718a2971c
--- /dev/null
+++ b/compiler/rustc_query_impl/src/values.rs
@@ -0,0 +1,45 @@
+use super::QueryCtxt;
+use rustc_middle::ty::{self, AdtSizedConstraint, Ty};
+
+pub(super) trait Value<'tcx>: Sized {
+    fn from_cycle_error(tcx: QueryCtxt<'tcx>) -> Self;
+}
+
+impl<'tcx, T> Value<'tcx> for T {
+    default fn from_cycle_error(tcx: QueryCtxt<'tcx>) -> T {
+        tcx.sess.abort_if_errors();
+        bug!("Value::from_cycle_error called without errors");
+    }
+}
+
+impl<'tcx> Value<'tcx> for Ty<'_> {
+    fn from_cycle_error(tcx: QueryCtxt<'tcx>) -> Self {
+        // SAFETY: This is never called when `Self` is not `Ty<'tcx>`.
+        // FIXME: Represent the above fact in the trait system somehow.
+        unsafe { std::mem::transmute::<Ty<'tcx>, Ty<'_>>(tcx.ty_error()) }
+    }
+}
+
+impl<'tcx> Value<'tcx> for ty::SymbolName<'_> {
+    fn from_cycle_error(tcx: QueryCtxt<'tcx>) -> Self {
+        // SAFETY: This is never called when `Self` is not `SymbolName<'tcx>`.
+        // FIXME: Represent the above fact in the trait system somehow.
+        unsafe {
+            std::mem::transmute::<ty::SymbolName<'tcx>, ty::SymbolName<'_>>(ty::SymbolName::new(
+                *tcx, "<error>",
+            ))
+        }
+    }
+}
+
+impl<'tcx> Value<'tcx> for AdtSizedConstraint<'_> {
+    fn from_cycle_error(tcx: QueryCtxt<'tcx>) -> Self {
+        // SAFETY: This is never called when `Self` is not `AdtSizedConstraint<'tcx>`.
+        // FIXME: Represent the above fact in the trait system somehow.
+        unsafe {
+            std::mem::transmute::<AdtSizedConstraint<'tcx>, AdtSizedConstraint<'_>>(
+                AdtSizedConstraint(tcx.intern_type_list(&[tcx.ty_error()])),
+            )
+        }
+    }
+}