src/libsyntax_ext/standard_library_imports.rs

   1 use syntax::{ast, attr};
   2 use syntax::edition::Edition;
   3 use syntax::ext::hygiene::MacroKind;
   4 use syntax::ptr::P;
   5 use syntax::source_map::{ExpnInfo, ExpnKind, dummy_spanned, respan};
   6 use syntax::symbol::{Ident, Symbol, kw, sym};
   7 use syntax_pos::DUMMY_SP;
   8
   9 use std::iter;
  10
  11 pub fn inject(
  12     mut krate: ast::Crate, alt_std_name: Option<&str>, edition: Edition
  13 ) -> (ast::Crate, Option<Symbol>) {
  14     let rust_2018 = edition >= Edition::Edition2018;
  15
  16     // the first name in this list is the crate name of the crate with the prelude
  17     let names: &[&str] = if attr::contains_name(&krate.attrs, sym::no_core) {
  18         return (krate, None);
  19     } else if attr::contains_name(&krate.attrs, sym::no_std) {
  20         if attr::contains_name(&krate.attrs, sym::compiler_builtins) {
  21             &["core"]
  22         } else {
  23             &["core", "compiler_builtins"]
  24         }
  25     } else {
  26         &["std"]
  27     };
  28
  29     // .rev() to preserve ordering above in combination with insert(0, ...)
  30     let alt_std_name = alt_std_name.map(Symbol::intern);
  31     for orig_name_str in names.iter().rev() {
  32         // HACK(eddyb) gensym the injected crates on the Rust 2018 edition,
  33         // so they don't accidentally interfere with the new import paths.
  34         let orig_name_sym = Symbol::intern(orig_name_str);
  35         let orig_name_ident = Ident::with_dummy_span(orig_name_sym);
  36         let (rename, orig_name) = if rust_2018 {
  37             (orig_name_ident.gensym(), Some(orig_name_sym))
  38         } else {
  39             (orig_name_ident, None)
  40         };
  41         krate.module.items.insert(0, P(ast::Item {
  42             attrs: vec![attr::mk_attr_outer(
  43                 attr::mk_word_item(ast::Ident::with_dummy_span(sym::macro_use))
  44             )],
  45             vis: dummy_spanned(ast::VisibilityKind::Inherited),
  46             node: ast::ItemKind::ExternCrate(alt_std_name.or(orig_name)),
  47             ident: rename,
  48             id: ast::DUMMY_NODE_ID,
  49             span: DUMMY_SP,
  50             tokens: None,
  51         }));
  52     }
  53
  54     // the crates have been injected, the assumption is that the first one is the one with
  55     // the prelude.
  56     let name = names[0];
  57
  58     let span = DUMMY_SP.fresh_expansion(ExpnInfo::allow_unstable(
  59         ExpnKind::Macro(MacroKind::Attr, sym::std_inject), DUMMY_SP, edition,
  60         [sym::prelude_import][..].into(),
  61     ));
  62
  63     krate.module.items.insert(0, P(ast::Item {
  64         attrs: vec![attr::mk_attr_outer(
  65             attr::mk_word_item(ast::Ident::new(sym::prelude_import, span)))],
  66         vis: respan(span.shrink_to_lo(), ast::VisibilityKind::Inherited),
  67         node: ast::ItemKind::Use(P(ast::UseTree {
  68             prefix: ast::Path {
  69                 segments: iter::once(ast::Ident::with_dummy_span(kw::PathRoot))
  70                     .chain(
  71                         [name, "prelude", "v1"].iter().cloned()
  72                             .map(ast::Ident::from_str)
  73                     ).map(ast::PathSegment::from_ident).collect(),
  74                 span,
  75             },
  76             kind: ast::UseTreeKind::Glob,
  77             span,
  78         })),
  79         id: ast::DUMMY_NODE_ID,
  80         ident: ast::Ident::invalid(),
  81         span,
  82         tokens: None,
  83     }));
  84
  85     (krate, Some(Symbol::intern(name)))
  86 }