Deprecate RustcEncodable and RustcDecodable.

library/core/src/macros/mod.rs

@@ -1468,6 +1468,10 @@ pub(crate) mod builtin {
     #[rustc_builtin_macro]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[allow_internal_unstable(core_intrinsics, libstd_sys_internals)]
+    #[rustc_deprecated(
+        since = "1.52.0",
+        reason = "rustc-serialize is deprecated and no longer supported"
+    )]
     pub macro RustcDecodable($item:item) {
         /* compiler built-in */
     }
@@ -1476,6 +1480,10 @@ pub(crate) mod builtin {
     #[rustc_builtin_macro]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[allow_internal_unstable(core_intrinsics)]
+    #[rustc_deprecated(
+        since = "1.52.0",
+        reason = "rustc-serialize is deprecated and no longer supported"
+    )]
     pub macro RustcEncodable($item:item) {
         /* compiler built-in */
     }

library/core/src/prelude/v1.rs

@@ -61,7 +61,7 @@ pub use crate::{
 };
 
 #[stable(feature = "builtin_macro_prelude", since = "1.38.0")]
-#[allow(deprecated)]
+#[allow(deprecated, deprecated_in_future)]
 #[doc(no_inline)]
 pub use crate::macros::builtin::{
     bench, global_allocator, test, test_case, RustcDecodable, RustcEncodable,

library/std/src/prelude/v1.rs

@@ -48,7 +48,7 @@ pub use core::prelude::v1::{
 // FIXME: Attribute and internal derive macros are not documented because for them rustdoc generates
 // dead links which fail link checker testing.
 #[stable(feature = "builtin_macro_prelude", since = "1.38.0")]
-#[allow(deprecated)]
+#[allow(deprecated, deprecated_in_future)]
 #[doc(hidden)]
 pub use core::prelude::v1::{
     bench, global_allocator, test, test_case, RustcDecodable, RustcEncodable,