1 files changed, 14 insertions, 0 deletions
diff --git a/compiler/rustc_typeck/src/variance/test.rs b/compiler/rustc_typeck/src/variance/test.rs
new file mode 100644
index 000000000..2ba87db88
--- /dev/null
+++ b/compiler/rustc_typeck/src/variance/test.rs
@@ -0,0 +1,14 @@
+use rustc_errors::struct_span_err;
+use rustc_middle::ty::TyCtxt;
+use rustc_span::symbol::sym;
+
+pub fn test_variance(tcx: TyCtxt<'_>) {
+    // For unit testing: check for a special "rustc_variance"
+    // attribute and report an error with various results if found.
+    for id in tcx.hir().items() {
+        if tcx.has_attr(id.def_id.to_def_id(), sym::rustc_variance) {
+            let variances_of = tcx.variances_of(id.def_id);
+            struct_span_err!(tcx.sess, tcx.def_span(id.def_id), E0208, "{:?}", variances_of).emit();
+        }
+    }
+}