src/libsyntax/std_inject.rs

   1 use crate::ast;
   2 use crate::attr;
   3 use crate::edition::Edition;
   4 use crate::ext::hygiene::{Mark, SyntaxContext};
   5 use crate::symbol::{Symbol, keywords, sym};
   6 use crate::source_map::{ExpnInfo, MacroAttribute, dummy_spanned, hygiene, respan};
   7 use crate::ptr::P;
   8 use crate::tokenstream::TokenStream;
   9
  10 use std::cell::Cell;
  11 use std::iter;
  12 use syntax_pos::{DUMMY_SP, Span};
  13
  14 /// Craft a span that will be ignored by the stability lint's
  15 /// call to source_map's `is_internal` check.
  16 /// The expanded code uses the unstable `#[prelude_import]` attribute.
  17 fn ignored_span(sp: Span) -> Span {
  18     let mark = Mark::fresh(Mark::root());
  19     mark.set_expn_info(ExpnInfo {
  20         call_site: DUMMY_SP,
  21         def_site: None,
  22         format: MacroAttribute(Symbol::intern("std_inject")),
  23         allow_internal_unstable: Some(vec![
  24             Symbol::intern("prelude_import"),
  25         ].into()),
  26         allow_internal_unsafe: false,
  27         local_inner_macros: false,
  28         edition: hygiene::default_edition(),
  29     });
  30     sp.with_ctxt(SyntaxContext::empty().apply_mark(mark))
  31 }
  32
  33 pub fn injected_crate_name() -> Option<&'static str> {
  34     INJECTED_CRATE_NAME.with(|name| name.get())
  35 }
  36
  37 thread_local! {
  38     // A `Symbol` might make more sense here, but it doesn't work, probably for
  39     // reasons relating to the use of thread-local storage for the Symbol
  40     // interner.
  41     static INJECTED_CRATE_NAME: Cell<Option<&'static str>> = Cell::new(None);
  42 }
  43
  44 pub fn maybe_inject_crates_ref(
  45     mut krate: ast::Crate,
  46     alt_std_name: Option<&str>,
  47     edition: Edition,
  48 ) -> ast::Crate {
  49     let rust_2018 = edition >= Edition::Edition2018;
  50
  51     // the first name in this list is the crate name of the crate with the prelude
  52     let names: &[&str] = if attr::contains_name(&krate.attrs, sym::no_core) {
  53         return krate;
  54     } else if attr::contains_name(&krate.attrs, sym::no_std) {
  55         if attr::contains_name(&krate.attrs, sym::compiler_builtins) {
  56             &["core"]
  57         } else {
  58             &["core", "compiler_builtins"]
  59         }
  60     } else {
  61         &["std"]
  62     };
  63
  64     // .rev() to preserve ordering above in combination with insert(0, ...)
  65     let alt_std_name = alt_std_name.map(Symbol::intern);
  66     for orig_name_str in names.iter().rev() {
  67         // HACK(eddyb) gensym the injected crates on the Rust 2018 edition,
  68         // so they don't accidentally interfere with the new import paths.
  69         let (rename, orig_name) = if rust_2018 {
  70             (Symbol::gensym(orig_name_str), Some(Symbol::intern(orig_name_str)))
  71         } else {
  72             (Symbol::intern(orig_name_str), None)
  73         };
  74         krate.module.items.insert(0, P(ast::Item {
  75             attrs: vec![attr::mk_attr_outer(
  76                 DUMMY_SP,
  77                 attr::mk_attr_id(),
  78                 attr::mk_word_item(ast::Ident::with_empty_ctxt(sym::macro_use))
  79             )],
  80             vis: dummy_spanned(ast::VisibilityKind::Inherited),
  81             node: ast::ItemKind::ExternCrate(alt_std_name.or(orig_name)),
  82             ident: ast::Ident::with_empty_ctxt(rename),
  83             id: ast::DUMMY_NODE_ID,
  84             span: DUMMY_SP,
  85             tokens: None,
  86         }));
  87     }
  88
  89     // the crates have been injected, the assumption is that the first one is the one with
  90     // the prelude.
  91     let name = names[0];
  92
  93     INJECTED_CRATE_NAME.with(|opt_name| opt_name.set(Some(name)));
  94
  95     let span = ignored_span(DUMMY_SP);
  96     krate.module.items.insert(0, P(ast::Item {
  97         attrs: vec![ast::Attribute {
  98             style: ast::AttrStyle::Outer,
  99             path: ast::Path::from_ident(ast::Ident::new(Symbol::intern("prelude_import"), span)),
 100             tokens: TokenStream::empty(),
 101             id: attr::mk_attr_id(),
 102             is_sugared_doc: false,
 103             span,
 104         }],
 105         vis: respan(span.shrink_to_lo(), ast::VisibilityKind::Inherited),
 106         node: ast::ItemKind::Use(P(ast::UseTree {
 107             prefix: ast::Path {
 108                 segments: iter::once(keywords::PathRoot.ident())
 109                     .chain(
 110                         [name, "prelude", "v1"].iter().cloned()
 111                             .map(ast::Ident::from_str)
 112                     ).map(ast::PathSegment::from_ident).collect(),
 113                 span,
 114             },
 115             kind: ast::UseTreeKind::Glob,
 116             span,
 117         })),
 118         id: ast::DUMMY_NODE_ID,
 119         ident: keywords::Invalid.ident(),
 120         span,
 121         tokens: None,
 122     }));
 123
 124     krate
 125 }