Rollup merge of rust-lang#82217 - m-ou-se:edition-prelude, r=nikomatsakis

Edition-specific preludes

This changes `{std,core}::prelude` to export edition-specific preludes under `rust_2015`, `rust_2018` and `rust_2021`. (As suggested in rust-lang#51418 (comment).) For now they all just re-export `v1::*`, but this allows us to add things to the 2021edition prelude soon.

This also changes the compiler to make the automatically injected prelude import dependent on the selected edition.

cc `@rust-lang/libs` `@djc`

Author: Dylan-DPC

core/src/prelude/mod.rs

@@ -1,5 +1,41 @@
 //! The libcore prelude
+//!
+//! This module is intended for users of libcore which do not link to libstd as
+//! well. This module is imported by default when `#![no_std]` is used in the
+//! same manner as the standard library's prelude.
 
 #![stable(feature = "core_prelude", since = "1.4.0")]
 
 pub mod v1;
+
+/// The 2015 version of the core prelude.
+///
+/// See the [module-level documentation](self) for more.
+#[unstable(feature = "prelude_2015", issue = "none")]
+pub mod rust_2015 {
+    #[unstable(feature = "prelude_2015", issue = "none")]
+    #[doc(no_inline)]
+    pub use super::v1::*;
+}
+
+/// The 2018 version of the core prelude.
+///
+/// See the [module-level documentation](self) for more.
+#[unstable(feature = "prelude_2018", issue = "none")]
+pub mod rust_2018 {
+    #[unstable(feature = "prelude_2018", issue = "none")]
+    #[doc(no_inline)]
+    pub use super::v1::*;
+}
+
+/// The 2021 version of the core prelude.
+///
+/// See the [module-level documentation](self) for more.
+#[unstable(feature = "prelude_2021", issue = "none")]
+pub mod rust_2021 {
+    #[unstable(feature = "prelude_2021", issue = "none")]
+    #[doc(no_inline)]
+    pub use super::v1::*;
+
+    // FIXME: Add more things.
+}

core/src/prelude/v1.rs

@@ -1,8 +1,6 @@
-//! The core prelude
+//! The first version of the core prelude.
 //!
-//! This module is intended for users of libcore which do not link to libstd as
-//! well. This module is imported by default when `#![no_std]` is used in the
-//! same manner as the standard library's prelude.
+//! See the [module-level documentation](super) for more.
 
 #![stable(feature = "core_prelude", since = "1.4.0")]
 

std/src/lib.rs

@@ -302,6 +302,7 @@
 #![feature(panic_internals)]
 #![feature(panic_unwind)]
 #![feature(pin_static_ref)]
+#![feature(prelude_2021)]
 #![feature(prelude_import)]
 #![feature(ptr_internals)]
 #![feature(raw)]

std/src/prelude/mod.rs

@@ -84,3 +84,37 @@
 #![stable(feature = "rust1", since = "1.0.0")]
 
 pub mod v1;
+
+/// The 2015 version of the prelude of The Rust Standard Library.
+///
+/// See the [module-level documentation](self) for more.
+#[unstable(feature = "prelude_2015", issue = "none")]
+pub mod rust_2015 {
+    #[unstable(feature = "prelude_2015", issue = "none")]
+    #[doc(no_inline)]
+    pub use super::v1::*;
+}
+
+/// The 2018 version of the prelude of The Rust Standard Library.
+///
+/// See the [module-level documentation](self) for more.
+#[unstable(feature = "prelude_2018", issue = "none")]
+pub mod rust_2018 {
+    #[unstable(feature = "prelude_2018", issue = "none")]
+    #[doc(no_inline)]
+    pub use super::v1::*;
+}
+
+/// The 2021 version of the prelude of The Rust Standard Library.
+///
+/// See the [module-level documentation](self) for more.
+#[unstable(feature = "prelude_2021", issue = "none")]
+pub mod rust_2021 {
+    #[unstable(feature = "prelude_2021", issue = "none")]
+    #[doc(no_inline)]
+    pub use super::v1::*;
+
+    #[unstable(feature = "prelude_2021", issue = "none")]
+    #[doc(no_inline)]
+    pub use core::prelude::rust_2021::*;
+}

std/src/prelude/v1.rs

@@ -1,6 +1,6 @@
 //! The first version of the prelude of The Rust Standard Library.
 //!
-//! See the [module-level documentation](../index.html) for more.
+//! See the [module-level documentation](super) for more.
 
 #![stable(feature = "rust1", since = "1.0.0")]