do not implement unsafe auto traits for types with unsafe fields

If a type has unsafe fields, its safety invariants are not simply
the conjunction of its field types' safety invariants. Consequently,
it's invalid to reason about the safety properties of these types
in a purely structural manner — i.e., the manner in which `auto`
traits are implemented.

Makes progress towards #132922.

1 files changed, 10 insertions, 0 deletions

diff --git a/tests/ui/unsafe-fields/unsafe-fields-parse.rs b/tests/ui/unsafe-fields/unsafe-fields-parse.rs
new file mode 100644
index 00000000000..67277731293
--- /dev/null
+++ b/tests/ui/unsafe-fields/unsafe-fields-parse.rs
@@ -0,0 +1,10 @@
+//@ compile-flags: --crate-type=lib
+#![allow(incomplete_features)]
+#![feature(unsafe_fields)]
+
+// Parse errors even *with* unsafe_fields, which would make the compiler early-exit otherwise.
+enum A {
+    TupleLike(unsafe u32), //~ ERROR
+}
+
+struct B(unsafe u32); //~ ERROR