Rollup merge of rust-lang#134272 - RalfJung:destabilize-rustc_encodable_decodable, r=oli-obk

Remove rustc_encodable_decodable feature

This has been shown in future-compat reports since Rust 1.79 (rust-lang#116016), released June 2024. Let's see if crater still finds any issues.

Part of rust-lang#134301.

Cc ``@rust-lang/libs-api``

Author: matthiaskrgr

core/src/macros/mod.rs

@@ -1831,32 +1831,4 @@ pub(crate) mod builtin {
     pub macro deref($pat:pat) {
         builtin # deref($pat)
     }
-
-    /// Derive macro for `rustc-serialize`. Should not be used in new code.
-    #[rustc_builtin_macro]
-    #[unstable(
-        feature = "rustc_encodable_decodable",
-        issue = "none",
-        soft,
-        reason = "derive macro for `rustc-serialize`; should not be used in new code"
-    )]
-    #[deprecated(since = "1.52.0", note = "rustc-serialize is deprecated and no longer supported")]
-    #[doc(hidden)] // While technically stable, using it is unstable, and deprecated. Hide it.
-    pub macro RustcDecodable($item:item) {
-        /* compiler built-in */
-    }
-
-    /// Derive macro for `rustc-serialize`. Should not be used in new code.
-    #[rustc_builtin_macro]
-    #[unstable(
-        feature = "rustc_encodable_decodable",
-        issue = "none",
-        soft,
-        reason = "derive macro for `rustc-serialize`; should not be used in new code"
-    )]
-    #[deprecated(since = "1.52.0", note = "rustc-serialize is deprecated and no longer supported")]
-    #[doc(hidden)] // While technically stable, using it is unstable, and deprecated. Hide it.
-    pub macro RustcEncodable($item:item) {
-        /* compiler built-in */
-    }
 }

core/src/prelude/mod.rs

@@ -18,16 +18,6 @@ mod common;
 pub mod v1 {
     #[stable(feature = "rust1", since = "1.0.0")]
     pub use super::common::*;
-
-    // Do not `doc(inline)` these `doc(hidden)` items.
-    #[unstable(
-        feature = "rustc_encodable_decodable",
-        issue = "none",
-        soft,
-        reason = "derive macro for `rustc-serialize`; should not be used in new code"
-    )]
-    #[allow(deprecated)]
-    pub use crate::macros::builtin::{RustcDecodable, RustcEncodable};
 }
 
 /// The 2015 version of the core prelude.

std/src/prelude/mod.rs

@@ -120,16 +120,6 @@ mod common;
 pub mod v1 {
     #[stable(feature = "rust1", since = "1.0.0")]
     pub use super::common::*;
-
-    // Do not `doc(inline)` these `doc(hidden)` items.
-    #[unstable(
-        feature = "rustc_encodable_decodable",
-        issue = "none",
-        soft,
-        reason = "derive macro for `rustc-serialize`; should not be used in new code"
-    )]
-    #[allow(deprecated)]
-    pub use core::prelude::v1::{RustcDecodable, RustcEncodable};
 }
 
 /// The 2015 version of the prelude of The Rust Standard Library.