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

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Edition-specific preludes

This changes `{std,core}::prelude` to export edition-specific preludes under `rust_2015`, `rust_2018` and `rust_2021`. (As suggested in https://github.com/rust-lang/rust/issues/51418#issuecomment-395630382.) 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`
This commit is contained in:
Dylan DPC 2021-03-10 17:55:38 +01:00 • committed by GitHub
commit 759204ffc4
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20 changed files with 113 additions and 33 deletions
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30
compiler/rustc_builtin_macros/src/standard_library_imports.rs
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@ -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,