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

compiler/rustc_builtin_macros/src/standard_library_imports.rs

@@ -2,7 +2,7 @@ use rustc_ast as ast;
 use rustc_expand::base::{ExtCtxt, ResolverExpand};
 use rustc_expand::expand::ExpansionConfig;
 use rustc_session::Session;
-use rustc_span::edition::Edition;
+use rustc_span::edition::Edition::*;
 use rustc_span::hygiene::AstPass;
 use rustc_span::symbol::{kw, sym, Ident, Symbol};
 use rustc_span::DUMMY_SP;
@@ -13,7 +13,7 @@ pub fn inject(
     sess: &Session,
     alt_std_name: Option<Symbol>,
 ) -> ast::Crate {
-    let rust_2018 = sess.parse_sess.edition >= Edition::Edition2018;
+    let edition = sess.parse_sess.edition;
 
     // the first name in this list is the crate name of the crate with the prelude
     let names: &[Symbol] = if sess.contains_name(&krate.attrs, sym::no_core) {
@@ -42,7 +42,11 @@ pub fn inject(
 
     // .rev() to preserve ordering above in combination with insert(0, ...)
     for &name in names.iter().rev() {
-        let ident = if rust_2018 { Ident::new(name, span) } else { Ident::new(name, call_site) };
+        let ident = if edition >= Edition2018 {
+            Ident::new(name, span)
+        } else {
+            Ident::new(name, call_site)
+        };
         krate.items.insert(
             0,
             cx.item(
@@ -58,14 +62,18 @@ pub fn inject(
     // the one with the prelude.
     let name = names[0];
 
-    let import_path = if rust_2018 {
-        [name, sym::prelude, sym::v1].iter().map(|symbol| Ident::new(*symbol, span)).collect()
-    } else {
-        [kw::PathRoot, name, sym::prelude, sym::v1]
-            .iter()
-            .map(|symbol| Ident::new(*symbol, span))
-            .collect()
-    };
+    let root = (edition == Edition2015).then(|| kw::PathRoot);
+
+    let import_path = root
+        .iter()
+        .chain(&[name, sym::prelude])
+        .chain(&[match edition {
+            Edition2015 => sym::rust_2015,
+            Edition2018 => sym::rust_2018,
+            Edition2021 => sym::rust_2021,
+        }])
+        .map(|&symbol| Ident::new(symbol, span))
+        .collect();
 
     let use_item = cx.item(
         span,

compiler/rustc_span/src/symbol.rs

@@ -958,8 +958,11 @@ symbols! {
         rt,
         rtm_target_feature,
         rust,
+        rust_2015,
         rust_2015_preview,
+        rust_2018,
         rust_2018_preview,
+        rust_2021,
         rust_2021_preview,
         rust_begin_unwind,
         rust_eh_catch_typeinfo,

library/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.
+}

library/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")]
 

library/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)]

library/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::*;
+}

library/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")]
 

src/test/pretty/asm.pp

@@ -2,7 +2,7 @@
 #![no_std]
 #![feature(asm)]
 #[prelude_import]
-use ::std::prelude::v1::*;
+use ::std::prelude::rust_2015::*;
 #[macro_use]
 extern crate std;
 

src/test/pretty/cast-lt.pp

@@ -1,7 +1,7 @@
 #![feature(prelude_import)]
 #![no_std]
 #[prelude_import]
-use ::std::prelude::v1::*;
+use ::std::prelude::rust_2015::*;
 #[macro_use]
 extern crate std;
 // pretty-compare-only

src/test/pretty/dollar-crate.pp

@@ -1,7 +1,7 @@
 #![feature(prelude_import)]
 #![no_std]
 #[prelude_import]
-use ::std::prelude::v1::*;
+use ::std::prelude::rust_2015::*;
 #[macro_use]
 extern crate std;
 // pretty-compare-only