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.

10 files changed, 60 insertions, 0 deletions

diff --git a/tests/ui/unsafe-fields/auto-traits.current.stderr b/tests/ui/unsafe-fields/auto-traits.current.stderr
new file mode 100644
index 00000000000..53a97458b7c
--- /dev/null
+++ b/tests/ui/unsafe-fields/auto-traits.current.stderr
@@ -0,0 +1,17 @@
+error[E0277]: the trait bound `UnsafeEnum: UnsafeAuto` is not satisfied
+  --> $DIR/auto-traits.rs:24:22
+   |
+LL |     impl_unsafe_auto(UnsafeEnum::Safe(42));
+   |     ---------------- ^^^^^^^^^^^^^^^^^^^^ the trait `UnsafeAuto` is not implemented for `UnsafeEnum`
+   |     |
+   |     required by a bound introduced by this call
+   |
+note: required by a bound in `impl_unsafe_auto`
+  --> $DIR/auto-traits.rs:20:29
+   |
+LL | fn impl_unsafe_auto(_: impl UnsafeAuto) {}
+   |                             ^^^^^^^^^^ required by this bound in `impl_unsafe_auto`
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0277`.
diff --git a/tests/ui/unsafe-fields/auto-traits.next.stderr b/tests/ui/unsafe-fields/auto-traits.next.stderr
new file mode 100644
index 00000000000..53a97458b7c
--- /dev/null
+++ b/tests/ui/unsafe-fields/auto-traits.next.stderr
@@ -0,0 +1,17 @@
+error[E0277]: the trait bound `UnsafeEnum: UnsafeAuto` is not satisfied
+  --> $DIR/auto-traits.rs:24:22
+   |
+LL |     impl_unsafe_auto(UnsafeEnum::Safe(42));
+   |     ---------------- ^^^^^^^^^^^^^^^^^^^^ the trait `UnsafeAuto` is not implemented for `UnsafeEnum`
+   |     |
+   |     required by a bound introduced by this call
+   |
+note: required by a bound in `impl_unsafe_auto`
+  --> $DIR/auto-traits.rs:20:29
+   |
+LL | fn impl_unsafe_auto(_: impl UnsafeAuto) {}
+   |                             ^^^^^^^^^^ required by this bound in `impl_unsafe_auto`
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0277`.
diff --git a/tests/ui/unsafe-fields/auto-traits.rs b/tests/ui/unsafe-fields/auto-traits.rs
new file mode 100644
index 00000000000..e15d0000079
--- /dev/null
+++ b/tests/ui/unsafe-fields/auto-traits.rs
@@ -0,0 +1,26 @@
+//@ compile-flags: --crate-type=lib
+//@ revisions: current next
+//@[next] compile-flags: -Znext-solver
+
+#![feature(auto_traits)]
+#![feature(unsafe_fields)]
+#![allow(incomplete_features)]
+
+enum UnsafeEnum {
+    Safe(u8),
+    Unsafe { unsafe field: u8 },
+}
+
+auto trait SafeAuto {}
+
+fn impl_safe_auto(_: impl SafeAuto) {}
+
+unsafe auto trait UnsafeAuto {}
+
+fn impl_unsafe_auto(_: impl UnsafeAuto) {}
+
+fn tests() {
+    impl_safe_auto(UnsafeEnum::Safe(42));
+    impl_unsafe_auto(UnsafeEnum::Safe(42));
+    //~^ ERROR the trait bound `UnsafeEnum: UnsafeAuto` is not satisfied
+}
diff --git a/tests/ui/auxiliary/unsafe-fields-crate-dep.rs b/tests/ui/unsafe-fields/auxiliary/unsafe-fields-crate-dep.rs
index 95b928402a9..95b928402a9 100644
--- a/tests/ui/auxiliary/unsafe-fields-crate-dep.rs
+++ b/tests/ui/unsafe-fields/auxiliary/unsafe-fields-crate-dep.rs
diff --git a/tests/ui/unsafe-fields-crate.rs b/tests/ui/unsafe-fields/unsafe-fields-crate.rs
index cfb9ad6b544..cfb9ad6b544 100644
--- a/tests/ui/unsafe-fields-crate.rs
+++ b/tests/ui/unsafe-fields/unsafe-fields-crate.rs
diff --git a/tests/ui/unsafe-fields-crate.stderr b/tests/ui/unsafe-fields/unsafe-fields-crate.stderr
index 778c26e0a43..778c26e0a43 100644
--- a/tests/ui/unsafe-fields-crate.stderr
+++ b/tests/ui/unsafe-fields/unsafe-fields-crate.stderr
diff --git a/tests/ui/unsafe-fields-parse.rs b/tests/ui/unsafe-fields/unsafe-fields-parse.rs
index 67277731293..67277731293 100644
--- a/tests/ui/unsafe-fields-parse.rs
+++ b/tests/ui/unsafe-fields/unsafe-fields-parse.rs
diff --git a/tests/ui/unsafe-fields-parse.stderr b/tests/ui/unsafe-fields/unsafe-fields-parse.stderr
index 5a45ab03ffe..5a45ab03ffe 100644
--- a/tests/ui/unsafe-fields-parse.stderr
+++ b/tests/ui/unsafe-fields/unsafe-fields-parse.stderr
diff --git a/tests/ui/unsafe-fields.rs b/tests/ui/unsafe-fields/unsafe-fields.rs
index 637471582d7..637471582d7 100644
--- a/tests/ui/unsafe-fields.rs
+++ b/tests/ui/unsafe-fields/unsafe-fields.rs
diff --git a/tests/ui/unsafe-fields.stderr b/tests/ui/unsafe-fields/unsafe-fields.stderr
index a1c5d2b44cd..a1c5d2b44cd 100644
--- a/tests/ui/unsafe-fields.stderr
+++ b/tests/ui/unsafe-fields/unsafe-fields.stderr