[derive] Test derives on deprecated types

Follows up on #1332
Makes progress on #553

zerocopy-derive/tests/deprecated.rs

@@ -0,0 +1,48 @@
+// Copyright 2024 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+// See comment in `include.rs` for why we disable the prelude.
+#![no_implicit_prelude]
+#![allow(warnings)]
+#![deny(deprecated)]
+
+include!("include.rs");
+
+// Make sure no deprecation warnings are generated from our derives (see #553).
+
+#[macro_export]
+macro_rules! test {
+    ($name:ident => $ty:item => $($trait:ident),*) => {
+        #[allow(non_snake_case)]
+        mod $name {
+            $(
+                mod $trait {
+                    use super::super::*;
+
+                    #[deprecated = "do not use"]
+                    #[derive(imp::$trait)]
+                    $ty
+
+                    #[allow(deprecated)]
+                    fn _allow_deprecated() {
+                        util_assert_impl_all!($name: imp::$trait);
+                    }
+                }
+            )*
+        }
+    };
+}
+
+// NOTE: `FromBytes` is tested separately in `enum_from_bytes.rs` since it
+// requires 256-variant enums which are extremely verbose; such enums are
+// already in that file.
+test!(Enum => #[repr(u8)] enum Enum { A, } => TryFromBytes, FromZeros, KnownLayout, Immutable, IntoBytes, Unaligned);
+
+test!(Struct => #[repr(C)] struct Struct; => TryFromBytes, FromZeros, FromBytes, KnownLayout, Immutable, IntoBytes, Unaligned);
+
+test!(Union => #[repr(C)] union Union{ a: (), } => TryFromBytes, FromZeros, FromBytes, KnownLayout, Immutable, IntoBytes, Unaligned);

zerocopy-derive/tests/enum_from_bytes.rs

@@ -9,6 +9,7 @@
 // See comment in `include.rs` for why we disable the prelude.
 #![no_implicit_prelude]
 #![allow(warnings)]
+#![deny(deprecated)]
 
 include!("include.rs");
 
@@ -29,6 +30,8 @@ include!("include.rs");
 // `Variant128` has a discriminant of -128) since Rust won't automatically wrap
 // a signed discriminant around without you explicitly telling it to.
 
+// Make sure no deprecation warning is generated from our derive (see #553).
+#[deprecated = "do not use"]
 #[derive(imp::FromBytes)]
 #[repr(u8)]
 enum FooU8 {
@@ -290,7 +293,10 @@ enum FooU8 {
     Variant255,
 }
 
-util_assert_impl_all!(FooU8: imp::FromBytes);
+#[allow(deprecated)]
+fn _allow_deprecated() {
+    util_assert_impl_all!(FooU8: imp::FromBytes);
+}
 
 #[derive(imp::FromBytes)]
 #[repr(i8)]