rustc_builtin_macros/
cfg.rs

1//! The compiler code necessary to support the cfg! extension, which expands to
2//! a literal `true` or `false` based on whether the given cfg matches the
3//! current compilation environment.
4
5use rustc_ast::tokenstream::TokenStream;
6use rustc_ast::{AttrStyle, token};
7use rustc_attr_parsing::parser::{AllowExprMetavar, MetaItemOrLitParser};
8use rustc_attr_parsing::{
9    self as attr, AttributeParser, CFG_TEMPLATE, ParsedDescription, ShouldEmit, parse_cfg_entry,
10};
11use rustc_expand::base::{DummyResult, ExpandResult, ExtCtxt, MacEager, MacroExpanderResult};
12use rustc_hir::attrs::CfgEntry;
13use rustc_hir::{AttrPath, Target};
14use rustc_parse::exp;
15use rustc_parse::parser::Recovery;
16use rustc_span::{ErrorGuaranteed, Span, sym};
17
18use crate::errors;
19
20pub(crate) fn expand_cfg(
21    cx: &mut ExtCtxt<'_>,
22    sp: Span,
23    tts: TokenStream,
24) -> MacroExpanderResult<'static> {
25    let sp = cx.with_def_site_ctxt(sp);
26
27    ExpandResult::Ready(match parse_cfg(cx, sp, tts) {
28        Ok(cfg) => {
29            let matches_cfg = attr::eval_config_entry(cx.sess, &cfg).as_bool();
30
31            MacEager::expr(cx.expr_bool(sp, matches_cfg))
32        }
33        Err(guar) => DummyResult::any(sp, guar),
34    })
35}
36
37fn parse_cfg(cx: &ExtCtxt<'_>, span: Span, tts: TokenStream) -> Result<CfgEntry, ErrorGuaranteed> {
38    let mut parser = cx.new_parser_from_tts(tts);
39    if parser.token == token::Eof {
40        return Err(cx.dcx().emit_err(errors::RequiresCfgPattern { span }));
41    }
42
43    let meta = MetaItemOrLitParser::parse_single(
44        &mut parser,
45        ShouldEmit::ErrorsAndLints { recovery: Recovery::Allowed },
46        AllowExprMetavar::Yes,
47    )
48    .map_err(|diag| diag.emit())?;
49    let cfg = AttributeParser::parse_single_args(
50        cx.sess,
51        span,
52        span,
53        AttrStyle::Inner,
54        AttrPath { segments: ::alloc::boxed::box_assume_init_into_vec_unsafe(::alloc::intrinsics::write_box_via_move(::alloc::boxed::Box::new_uninit(),
        [sym::cfg]))vec![sym::cfg].into_boxed_slice(), span },
55        None,
56        ParsedDescription::Macro,
57        span,
58        cx.current_expansion.lint_node_id,
59        // Doesn't matter what the target actually is here.
60        Target::Crate,
61        Some(cx.ecfg.features),
62        ShouldEmit::ErrorsAndLints { recovery: Recovery::Allowed },
63        &meta,
64        parse_cfg_entry,
65        &CFG_TEMPLATE,
66    )?;
67
68    let _ = parser.eat(::rustc_parse::parser::token_type::ExpTokenPair {
    tok: rustc_ast::token::Comma,
    token_type: ::rustc_parse::parser::token_type::TokenType::Comma,
}exp!(Comma));
69
70    if !parser.eat(::rustc_parse::parser::token_type::ExpTokenPair {
    tok: rustc_ast::token::Eof,
    token_type: ::rustc_parse::parser::token_type::TokenType::Eof,
}exp!(Eof)) {
71        return Err(cx.dcx().emit_err(errors::OneCfgPattern { span }));
72    }
73
74    Ok(cfg)
75}
rustc_builtin_macros/cfg.rs

rustc_builtin_macros/
cfg.rs
