src/libsyntax_ext/standard_library_imports.rs

   1 use syntax::{ast, attr};
   2 use syntax::edition::Edition;
   3 use syntax::ptr::P;
   4 use syntax::sess::ParseSess;
   5 use syntax::symbol::{Ident, Symbol, kw, sym};
   6 use syntax_expand::expand::ExpansionConfig;
   7 use syntax_expand::base::{ExtCtxt, Resolver};
   8 use syntax_pos::DUMMY_SP;
   9 use syntax_pos::hygiene::AstPass;
  10
  11 pub fn inject(
  12     mut krate: ast::Crate,
  13     resolver: &mut dyn Resolver,
  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);
  43
  44
  45     // .rev() to preserve ordering above in combination with insert(0, ...)
  46     for &name in names.iter().rev() {
  47         let ident = if rust_2018 {
  48             Ident::new(name, span)
  49         } else {
  50             Ident::new(name, call_site)
  51         };
  52         krate.module.items.insert(0, 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     // 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 import_path = if rust_2018 {
  65         [name, sym::prelude, sym::v1].iter()
  66             .map(|symbol| ast::Ident::new(*symbol, span)).collect()
  67     } else {
  68         [kw::PathRoot, name, sym::prelude, sym::v1].iter()
  69             .map(|symbol| ast::Ident::new(*symbol, span)).collect()
  70     };
  71
  72     let use_item = cx.item(
  73         span,
  74         ast::Ident::invalid(),
  75         vec![cx.attribute(cx.meta_word(span, sym::prelude_import))],
  76         ast::ItemKind::Use(P(ast::UseTree {
  77             prefix: cx.path(span, import_path),
  78             kind: ast::UseTreeKind::Glob,
  79             span,
  80         })),
  81     );
  82
  83     krate.module.items.insert(0, use_item);
  84
  85     (krate, Some(name))
  86 }