Destabilize RustcEncodable and RustcDecodable

library/core/src/lib.rs

@@ -151,6 +151,7 @@
 #![feature(variant_count)]
 #![feature(const_array_from_ref)]
 #![feature(const_slice_from_ref)]
+#![feature(rustc_encodable_decodable)]
 //
 // Language features:
 #![feature(abi_unadjusted)]

library/core/src/macros/mod.rs

@@ -1508,26 +1508,34 @@ pub(crate) mod builtin {
 
     /// Unstable implementation detail of the `rustc` compiler, do not use.
     #[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"
     )]
     #[doc(hidden)] // While technically stable, using it is unstable, and deprecated. Hide it.
+    #[unstable(
+        feature = "rustc_encodable_decodable",
+        issue = "none",
+        reason = "RustcDecodable cannot be used stably"
+    )]
     pub macro RustcDecodable($item:item) {
         /* compiler built-in */
     }
 
     /// Unstable implementation detail of the `rustc` compiler, do not use.
     #[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"
     )]
     #[doc(hidden)] // While technically stable, using it is unstable, and deprecated. Hide it.
+    #[unstable(
+        feature = "rustc_encodable_decodable",
+        issue = "none",
+        reason = "RustcDecodable cannot be used stably"
+    )]
     pub macro RustcEncodable($item:item) {
         /* compiler built-in */
     }

library/std/src/lib.rs

@@ -321,6 +321,7 @@
 #![feature(ptr_internals)]
 #![feature(rustc_attrs)]
 #![feature(rustc_private)]
+#![feature(rustc_encodable_decodable)]
 #![feature(saturating_int_impl)]
 #![feature(slice_concat_ext)]
 #![feature(slice_internals)]

library/std/src/prelude/v1.rs

@@ -55,7 +55,7 @@ pub use core::prelude::v1::{
 pub use core::prelude::v1::concat_bytes;
 
 // Do not `doc(inline)` these `doc(hidden)` items.
-#[stable(feature = "builtin_macro_prelude", since = "1.38.0")]
+#[unstable(feature = "rustc_encodable_decodable", issue = "none")]
 #[allow(deprecated)]
 pub use core::prelude::v1::{RustcDecodable, RustcEncodable};
 

src/test/run-make-fulldeps/pretty-expanded/input.rs

@@ -1,6 +1,6 @@
-#[crate_type="lib"]
-
-// #13544
+// FIXME: This should be replaced with some other derive macro
+#![feature(rustc_encodable_decodable)]
+#[crate_type="lib"] // Why is this an outer attribute?
 
 extern crate rustc_serialize;