src/librustc_builtin_macros/standard_library_imports.rs

   1 use rustc_ast::ptr::P;
   2 use rustc_ast::{ast, attr};
   3 use rustc_expand::base::{ExtCtxt, ResolverExpand};
   4 use rustc_expand::expand::ExpansionConfig;
   5 use rustc_session::parse::ParseSess;
   6 use rustc_span::edition::Edition;
   7 use rustc_span::hygiene::AstPass;
   8 use rustc_span::symbol::{kw, sym, Ident, Symbol};
   9 use rustc_span::DUMMY_SP;
  10
  11 pub fn inject(
  12     mut krate: ast::Crate,
  13     resolver: &mut dyn ResolverExpand,
  14     sess: &ParseSess,
  15     alt_std_name: Option<Symbol>,
  16 ) -> (ast::Crate, Option<Symbol>) {
  17     let rust_2018 = sess.edition >= Edition::Edition2018;
  18
  19     // the first name in this list is the crate name of the crate with the prelude
  20     let names: &[Symbol] = if attr::contains_name(&krate.attrs, sym::no_core) {
  21         return (krate, None);
  22     } else if attr::contains_name(&krate.attrs, sym::no_std) {
  23         if attr::contains_name(&krate.attrs, sym::compiler_builtins) {
  24             &[sym::core]
  25         } else {
  26             &[sym::core, sym::compiler_builtins]
  27         }
  28     } else {
  29         &[sym::std]
  30     };
  31
  32     let expn_id = resolver.expansion_for_ast_pass(
  33         DUMMY_SP,
  34         AstPass::StdImports,
  35         &[sym::prelude_import],
  36         None,
  37     );
  38     let span = DUMMY_SP.with_def_site_ctxt(expn_id);
  39     let call_site = DUMMY_SP.with_call_site_ctxt(expn_id);
  40
  41     let ecfg = ExpansionConfig::default("std_lib_injection".to_string());
  42     let cx = ExtCtxt::new(sess, ecfg, resolver, None);
  43
  44     // .rev() to preserve ordering above in combination with insert(0, ...)
  45     for &name in names.iter().rev() {
  46         let ident = if rust_2018 { Ident::new(name, span) } else { Ident::new(name, call_site) };
  47         krate.module.items.insert(
  48             0,
  49             cx.item(
  50                 span,
  51                 ident,
  52                 vec![cx.attribute(cx.meta_word(span, sym::macro_use))],
  53                 ast::ItemKind::ExternCrate(alt_std_name),
  54             ),
  55         );
  56     }
  57
  58     // The crates have been injected, the assumption is that the first one is
  59     // the one with the prelude.
  60     let name = names[0];
  61
  62     let import_path = if rust_2018 {
  63         [name, sym::prelude, sym::v1].iter().map(|symbol| Ident::new(*symbol, span)).collect()
  64     } else {
  65         [kw::PathRoot, name, sym::prelude, sym::v1]
  66             .iter()
  67             .map(|symbol| Ident::new(*symbol, span))
  68             .collect()
  69     };
  70
  71     let use_item = cx.item(
  72         span,
  73         Ident::invalid(),
  74         vec![cx.attribute(cx.meta_word(span, sym::prelude_import))],
  75         ast::ItemKind::Use(P(ast::UseTree {
  76             prefix: cx.path(span, import_path),
  77             kind: ast::UseTreeKind::Glob,
  78             span,
  79         })),
  80     );
  81
  82     krate.module.items.insert(0, use_item);
  83
  84     (krate, Some(name))
  85 }