compiler/rustc_builtin_macros/src/standard_library_imports.rs

   1 use rustc_ast as ast;
   2 use rustc_expand::base::{ExtCtxt, ResolverExpand};
   3 use rustc_expand::expand::ExpansionConfig;
   4 use rustc_session::Session;
   5 use rustc_span::edition::Edition::*;
   6 use rustc_span::hygiene::AstPass;
   7 use rustc_span::symbol::{kw, sym, Ident, Symbol};
   8 use rustc_span::DUMMY_SP;
   9
  10 pub fn inject(
  11     mut krate: ast::Crate,
  12     resolver: &mut dyn ResolverExpand,
  13     sess: &Session,
  14 ) -> ast::Crate {
  15     let edition = sess.parse_sess.edition;
  16
  17     // the first name in this list is the crate name of the crate with the prelude
  18     let names: &[Symbol] = if sess.contains_name(&krate.attrs, sym::no_core) {
  19         return krate;
  20     } else if sess.contains_name(&krate.attrs, sym::no_std) {
  21         if sess.contains_name(&krate.attrs, sym::compiler_builtins) {
  22             &[sym::core]
  23         } else {
  24             &[sym::core, sym::compiler_builtins]
  25         }
  26     } else {
  27         &[sym::std]
  28     };
  29
  30     let expn_id = resolver.expansion_for_ast_pass(
  31         DUMMY_SP,
  32         AstPass::StdImports,
  33         &[sym::prelude_import],
  34         None,
  35     );
  36     let span = DUMMY_SP.with_def_site_ctxt(expn_id.to_expn_id());
  37     let call_site = DUMMY_SP.with_call_site_ctxt(expn_id.to_expn_id());
  38
  39     let ecfg = ExpansionConfig::default("std_lib_injection".to_string());
  40     let cx = ExtCtxt::new(sess, ecfg, resolver, None);
  41
  42     // .rev() to preserve ordering above in combination with insert(0, ...)
  43     for &name in names.iter().rev() {
  44         let ident = if edition >= Edition2018 {
  45             Ident::new(name, span)
  46         } else {
  47             Ident::new(name, call_site)
  48         };
  49         krate.items.insert(
  50             0,
  51             cx.item(
  52                 span,
  53                 ident,
  54                 vec![cx.attribute(cx.meta_word(span, sym::macro_use))],
  55                 ast::ItemKind::ExternCrate(None),
  56             ),
  57         );
  58     }
  59
  60     // The crates have been injected, the assumption is that the first one is
  61     // the one with the prelude.
  62     let name = names[0];
  63
  64     let root = (edition == Edition2015).then(|| kw::PathRoot);
  65
  66     let import_path = root
  67         .iter()
  68         .chain(&[name, sym::prelude])
  69         .chain(&[match edition {
  70             Edition2015 => sym::rust_2015,
  71             Edition2018 => sym::rust_2018,
  72             Edition2021 => sym::rust_2021,
  73             Edition2024 => sym::rust_2024,
  74         }])
  75         .map(|&symbol| Ident::new(symbol, span))
  76         .collect();
  77
  78     let use_item = cx.item(
  79         span,
  80         Ident::empty(),
  81         vec![cx.attribute(cx.meta_word(span, sym::prelude_import))],
  82         ast::ItemKind::Use(ast::UseTree {
  83             prefix: cx.path(span, import_path),
  84             kind: ast::UseTreeKind::Glob,
  85             span,
  86         }),
  87     );
  88
  89     krate.items.insert(0, use_item);
  90
  91     krate
  92 }