Rollup merge of rust-lang#102049 - fee1-dead-contrib:derive_const, r=oli-obk

Add the `#[derive_const]` attribute

Closes rust-lang#102371. This is a minimal patchset for the attribute to work. There are no restrictions on what traits this attribute applies to.

r? `````@oli-obk`````

Author: Dylan-DPC

core/src/macros/mod.rs

@@ -1464,6 +1464,19 @@ pub(crate) mod builtin {
         /* compiler built-in */
     }
 
+    /// Attribute macro used to apply derive macros for implementing traits
+    /// in a const context.
+    ///
+    /// See [the reference] for more info.
+    ///
+    /// [the reference]: ../../../reference/attributes/derive.html
+    #[unstable(feature = "derive_const", issue = "none")]
+    #[rustc_builtin_macro]
+    #[cfg(not(bootstrap))]
+    pub macro derive_const($item:item) {
+        /* compiler built-in */
+    }
+
     /// Attribute macro applied to a function to turn it into a unit test.
     ///
     /// See [the reference] for more info.

core/src/prelude/v1.rs

@@ -81,6 +81,10 @@ pub use crate::macros::builtin::alloc_error_handler;
 #[stable(feature = "builtin_macro_prelude", since = "1.38.0")]
 pub use crate::macros::builtin::{bench, derive, global_allocator, test, test_case};
 
+#[unstable(feature = "derive_const", issue = "none")]
+#[cfg(not(bootstrap))]
+pub use crate::macros::builtin::derive_const;
+
 #[unstable(
     feature = "cfg_accessible",
     issue = "64797",

std/src/prelude/v1.rs

@@ -65,6 +65,10 @@ pub use core::prelude::v1::alloc_error_handler;
 #[stable(feature = "builtin_macro_prelude", since = "1.38.0")]
 pub use core::prelude::v1::{bench, derive, global_allocator, test, test_case};
 
+#[unstable(feature = "derive_const", issue = "none")]
+#[cfg(not(bootstrap))]
+pub use core::prelude::v1::derive_const;
+
 // Do not `doc(no_inline)` either.
 #[unstable(
     feature = "cfg_accessible",