Auto merge of #116016 - jhpratt:kill-rustc-serialize, r=ehuss

Soft-destabilize `RustcEncodable` & `RustcDecodable`, remove from prelude in next edition

cc rust-lang/libs-team#272

Any use of `RustcEncodable` and `RustcDecodable` now triggers a deny-by-default lint. The derives have been removed from the 2024 prelude. I specifically chose **not** to document this in the module-level documentation, as the presence in existing preludes is not documented (which I presume is intentional).

This does not implement the proposed change for `rustfix`, which I will be looking into shortly.

With regard to the items in the preludes being stable, this should not be an issue because #15702 has been resolved.

r? libs-api

8 files changed, 156 insertions, 40 deletions

diff --git a/library/core/src/macros/mod.rs b/library/core/src/macros/mod.rs
index a78842c8f8d..574a357b44a 100644
--- a/library/core/src/macros/mod.rs
+++ b/library/core/src/macros/mod.rs
@@ -1726,20 +1726,28 @@ pub(crate) mod builtin {
         builtin # deref($pat)
     }
 
-    /// Unstable implementation detail of the `rustc` compiler, do not use.
+    /// Derive macro for `rustc-serialize`. Should not be used in new code.
     #[rustc_builtin_macro]
-    #[stable(feature = "rust1", since = "1.0.0")]
-    #[allow_internal_unstable(core_intrinsics, libstd_sys_internals, rt)]
+    #[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 */
     }
 
-    /// Unstable implementation detail of the `rustc` compiler, do not use.
+    /// Derive macro for `rustc-serialize`. Should not be used in new code.
     #[rustc_builtin_macro]
-    #[stable(feature = "rust1", since = "1.0.0")]
-    #[allow_internal_unstable(core_intrinsics, rt)]
+    #[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) {
diff --git a/library/core/src/prelude/v1.rs b/library/core/src/prelude/common.rs
index 29f73bb4942..b98f3a4659b 100644
--- a/library/core/src/prelude/v1.rs
+++ b/library/core/src/prelude/common.rs
@@ -1,9 +1,7 @@
-//! The first version of the core prelude.
+//! Items common to the prelude of all editions.
 //!
 //! See the [module-level documentation](super) for more.
 
-#![stable(feature = "core_prelude", since = "1.4.0")]
-
 // Re-exported core operators
 #[stable(feature = "core_prelude", since = "1.4.0")]
 #[doc(no_inline)]
@@ -68,11 +66,6 @@ pub use crate::{
 #[doc(no_inline)]
 pub use crate::concat_bytes;
 
-// Do not `doc(inline)` these `doc(hidden)` items.
-#[stable(feature = "builtin_macro_prelude", since = "1.38.0")]
-#[allow(deprecated)]
-pub use crate::macros::builtin::{RustcDecodable, RustcEncodable};
-
 // Do not `doc(no_inline)` so that they become doc items on their own
 // (no public module for them to be re-exported from).
 #[stable(feature = "builtin_macro_prelude", since = "1.38.0")]
diff --git a/library/core/src/prelude/mod.rs b/library/core/src/prelude/mod.rs
index b4791c2c022..ca33ef160e8 100644
--- a/library/core/src/prelude/mod.rs
+++ b/library/core/src/prelude/mod.rs
@@ -6,7 +6,26 @@
 
 #![stable(feature = "core_prelude", since = "1.4.0")]
 
-pub mod v1;
+mod common;
+
+/// The first version of the prelude of The Rust Standard Library.
+///
+/// See the [module-level documentation](self) for more.
+#[stable(feature = "rust1", since = "1.0.0")]
+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.
 ///
@@ -46,14 +65,21 @@ pub mod rust_2021 {
     pub use crate::convert::{TryFrom, TryInto};
 }
 
-/// The 2024 edition of the core prelude.
+/// The 2024 version of the core prelude.
 ///
 /// See the [module-level documentation](self) for more.
 #[unstable(feature = "prelude_2024", issue = "121042")]
 pub mod rust_2024 {
-    #[unstable(feature = "prelude_2024", issue = "121042")]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub use super::common::*;
+
+    #[stable(feature = "prelude_2021", since = "1.55.0")]
+    #[doc(no_inline)]
+    pub use crate::iter::FromIterator;
+
+    #[stable(feature = "prelude_2021", since = "1.55.0")]
     #[doc(no_inline)]
-    pub use super::rust_2021::*;
+    pub use crate::convert::{TryFrom, TryInto};
 
     #[unstable(feature = "prelude_2024", issue = "121042")]
     #[doc(no_inline)]
diff --git a/library/std/src/prelude/v1.rs b/library/std/src/prelude/common.rs
index 36fa4e88b5b..f61e04e02b6 100644
--- a/library/std/src/prelude/v1.rs
+++ b/library/std/src/prelude/common.rs
@@ -1,9 +1,7 @@
-//! The first version of the prelude of The Rust Standard Library.
+//! Items common to the prelude of all editions.
 //!
 //! See the [module-level documentation](super) for more.
 
-#![stable(feature = "rust1", since = "1.0.0")]
-
 // Re-exported core operators
 #[stable(feature = "rust1", since = "1.0.0")]
 #[doc(no_inline)]
@@ -52,11 +50,6 @@ pub use core::prelude::v1::{
 #[doc(no_inline)]
 pub use core::prelude::v1::concat_bytes;
 
-// Do not `doc(inline)` these `doc(hidden)` items.
-#[stable(feature = "builtin_macro_prelude", since = "1.38.0")]
-#[allow(deprecated)]
-pub use core::prelude::v1::{RustcDecodable, RustcEncodable};
-
 // Do not `doc(no_inline)` so that they become doc items on their own
 // (no public module for them to be re-exported from).
 #[stable(feature = "builtin_macro_prelude", since = "1.38.0")]
diff --git a/library/std/src/prelude/mod.rs b/library/std/src/prelude/mod.rs
index 7d44d2e4b5d..0bdbab716ad 100644
--- a/library/std/src/prelude/mod.rs
+++ b/library/std/src/prelude/mod.rs
@@ -93,7 +93,26 @@
 
 #![stable(feature = "rust1", since = "1.0.0")]
 
-pub mod v1;
+mod common;
+
+/// The first version of the prelude of The Rust Standard Library.
+///
+/// See the [module-level documentation](self) for more.
+#[stable(feature = "rust1", since = "1.0.0")]
+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.
 ///
@@ -134,9 +153,8 @@ pub mod rust_2021 {
 /// See the [module-level documentation](self) for more.
 #[unstable(feature = "prelude_2024", issue = "121042")]
 pub mod rust_2024 {
-    #[unstable(feature = "prelude_2024", issue = "121042")]
-    #[doc(no_inline)]
-    pub use super::v1::*;
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub use super::common::*;
 
     #[unstable(feature = "prelude_2024", issue = "121042")]
     #[doc(no_inline)]
diff --git a/tests/run-make-fulldeps/pretty-expanded/input.rs b/tests/run-make-fulldeps/pretty-expanded/input.rs
index af3d75b3bf2..02b235068a1 100644
--- a/tests/run-make-fulldeps/pretty-expanded/input.rs
+++ b/tests/run-make-fulldeps/pretty-expanded/input.rs
@@ -1,12 +1,8 @@
-#[crate_type="lib"]
-
 // #13544
 
-extern crate rustc_serialize;
-
-#[derive(RustcEncodable)] pub struct A;
-#[derive(RustcEncodable)] pub struct B(isize);
-#[derive(RustcEncodable)] pub struct C { x: isize }
-#[derive(RustcEncodable)] pub enum D {}
-#[derive(RustcEncodable)] pub enum E { y }
-#[derive(RustcEncodable)] pub enum F { z(isize) }
+#[derive(Debug)] pub struct A;
+#[derive(Debug)] pub struct B(isize);
+#[derive(Debug)] pub struct C { x: isize }
+#[derive(Debug)] pub enum D {}
+#[derive(Debug)] pub enum E { y }
+#[derive(Debug)] pub enum F { z(isize) }
diff --git a/tests/ui/feature-gates/feature-gate-rustc_encodable_decodable.rs b/tests/ui/feature-gates/feature-gate-rustc_encodable_decodable.rs
new file mode 100644
index 00000000000..13f8fd5fe22
--- /dev/null
+++ b/tests/ui/feature-gates/feature-gate-rustc_encodable_decodable.rs
@@ -0,0 +1,16 @@
+#![crate_type = "lib"]
+
+// This isn't intended to compile, so it's easiest to just ignore this error.
+extern crate rustc_serialize; //~ERROR can't find crate for `rustc_serialize`
+
+#[derive(
+    RustcEncodable,
+    //~^   ERROR   use of unstable library feature 'rustc_encodable_decodable'
+    //~^^  WARNING this was previously accepted by the compiler
+    //~^^^ WARNING use of deprecated macro `RustcEncodable`
+    RustcDecodable,
+    //~^   ERROR   use of unstable library feature 'rustc_encodable_decodable'
+    //~^^  WARNING this was previously accepted by the compiler
+    //~^^^ WARNING use of deprecated macro `RustcDecodable`
+)]
+struct S;
diff --git a/tests/ui/feature-gates/feature-gate-rustc_encodable_decodable.stderr b/tests/ui/feature-gates/feature-gate-rustc_encodable_decodable.stderr
new file mode 100644
index 00000000000..02b74dacf4d
--- /dev/null
+++ b/tests/ui/feature-gates/feature-gate-rustc_encodable_decodable.stderr
@@ -0,0 +1,66 @@
+error[E0463]: can't find crate for `rustc_serialize`
+  --> $DIR/feature-gate-rustc_encodable_decodable.rs:4:1
+   |
+LL | extern crate rustc_serialize;
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ can't find crate
+   |
+   = help: maybe you need to install the missing components with: `rustup component add rust-src rustc-dev llvm-tools-preview`
+
+error: use of unstable library feature 'rustc_encodable_decodable': derive macro for `rustc-serialize`; should not be used in new code
+  --> $DIR/feature-gate-rustc_encodable_decodable.rs:7:5
+   |
+LL |     RustcEncodable,
+   |     ^^^^^^^^^^^^^^
+   |
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = note: for more information, see issue #64266 <https://github.com/rust-lang/rust/issues/64266>
+   = note: `#[deny(soft_unstable)]` on by default
+
+warning: use of deprecated macro `RustcEncodable`: rustc-serialize is deprecated and no longer supported
+  --> $DIR/feature-gate-rustc_encodable_decodable.rs:7:5
+   |
+LL |     RustcEncodable,
+   |     ^^^^^^^^^^^^^^
+   |
+   = note: `#[warn(deprecated)]` on by default
+
+error: use of unstable library feature 'rustc_encodable_decodable': derive macro for `rustc-serialize`; should not be used in new code
+  --> $DIR/feature-gate-rustc_encodable_decodable.rs:11:5
+   |
+LL |     RustcDecodable,
+   |     ^^^^^^^^^^^^^^
+   |
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = note: for more information, see issue #64266 <https://github.com/rust-lang/rust/issues/64266>
+
+warning: use of deprecated macro `RustcDecodable`: rustc-serialize is deprecated and no longer supported
+  --> $DIR/feature-gate-rustc_encodable_decodable.rs:11:5
+   |
+LL |     RustcDecodable,
+   |     ^^^^^^^^^^^^^^
+
+error: aborting due to 3 previous errors; 2 warnings emitted
+
+For more information about this error, try `rustc --explain E0463`.
+Future incompatibility report: Future breakage diagnostic:
+error: use of unstable library feature 'rustc_encodable_decodable': derive macro for `rustc-serialize`; should not be used in new code
+  --> $DIR/feature-gate-rustc_encodable_decodable.rs:7:5
+   |
+LL |     RustcEncodable,
+   |     ^^^^^^^^^^^^^^
+   |
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = note: for more information, see issue #64266 <https://github.com/rust-lang/rust/issues/64266>
+   = note: `#[deny(soft_unstable)]` on by default
+
+Future breakage diagnostic:
+error: use of unstable library feature 'rustc_encodable_decodable': derive macro for `rustc-serialize`; should not be used in new code
+  --> $DIR/feature-gate-rustc_encodable_decodable.rs:11:5
+   |
+LL |     RustcDecodable,
+   |     ^^^^^^^^^^^^^^
+   |
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = note: for more information, see issue #64266 <https://github.com/rust-lang/rust/issues/64266>
+   = note: `#[deny(soft_unstable)]` on by default
+