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     alt_std_name: Option<Symbol>,
  15 ) -> ast::Crate {
  16     let edition = sess.parse_sess.edition;
  17
  18     // the first name in this list is the crate name of the crate with the prelude
  19     let names: &[Symbol] = if sess.contains_name(&krate.attrs, sym::no_core) {
  20         return krate;
  21     } else if sess.contains_name(&krate.attrs, sym::no_std) {
  22         if sess.contains_name(&krate.attrs, sym::compiler_builtins) {
  23             &[sym::core]
  24         } else {
  25             &[sym::core, sym::compiler_builtins]
  26         }
  27     } else {
  28         &[sym::std]
  29     };
  30
  31     let expn_id = resolver.expansion_for_ast_pass(
  32         DUMMY_SP,
  33         AstPass::StdImports,
  34         &[sym::prelude_import],
  35         None,
  36     );
  37     let span = DUMMY_SP.with_def_site_ctxt(expn_id.to_expn_id());
  38     let call_site = DUMMY_SP.with_call_site_ctxt(expn_id.to_expn_id());
  39
  40     let ecfg = ExpansionConfig::default("std_lib_injection".to_string());
  41     let cx = ExtCtxt::new(sess, ecfg, resolver, None);
  42
  43     // .rev() to preserve ordering above in combination with insert(0, ...)
  44     for &name in names.iter().rev() {
  45         let ident = if edition >= Edition2018 {
  46             Ident::new(name, span)
  47         } else {
  48             Ident::new(name, call_site)
  49         };
  50         krate.items.insert(
  51             0,
  52             cx.item(
  53                 span,
  54                 ident,
  55                 vec![cx.attribute(cx.meta_word(span, sym::macro_use))],
  56                 ast::ItemKind::ExternCrate(alt_std_name),
  57             ),
  58         );
  59     }
  60
  61     // The crates have been injected, the assumption is that the first one is
  62     // the one with the prelude.
  63     let name = names[0];
  64
  65     let root = (edition == Edition2015).then(|| kw::PathRoot);
  66
  67     let import_path = root
  68         .iter()
  69         .chain(&[name, sym::prelude])
  70         .chain(&[match edition {
  71             Edition2015 => sym::rust_2015,
  72             Edition2018 => sym::rust_2018,
  73             Edition2021 => sym::rust_2021,
  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 }