add known-bug test for unsound issue 100041

Author: whtahy

tests/ui/wf/wf-normalization-sized.rs

@@ -0,0 +1,19 @@
+// check-pass
+// known-bug: #100041
+
+// Should fail. Normalization can bypass well-formedness checking.
+// `[[[[[[u8]]]]]]` is not a well-formed type since size of type `[u8]` cannot
+// be known at compile time (since `Sized` is not implemented for `[u8]`).
+
+trait WellUnformed {
+    type RequestNormalize;
+}
+
+impl<T: ?Sized> WellUnformed for T {
+    type RequestNormalize = ();
+}
+
+const _: <[[[[[[u8]]]]]] as WellUnformed>::RequestNormalize = ();
+const _: <Vec<str> as WellUnformed>::RequestNormalize = ();
+
+fn main() {}