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use rustc_ast::tokenstream::TokenStream;
use rustc_attr_parsing as attr;
use rustc_expand::base::{DummyResult, ExpandResult, ExtCtxt, MacroExpanderResult};
use rustc_parse::parser::cfg_select::{CfgSelectBranches, CfgSelectRule, parse_cfg_select};
use rustc_span::{Ident, Span, sym};
use crate::errors::{CfgSelectNoMatches, CfgSelectUnreachable};
/// Selects the first arm whose rule evaluates to true.
fn select_arm(ecx: &ExtCtxt<'_>, branches: CfgSelectBranches) -> Option<(TokenStream, Span)> {
for (cfg, tt, arm_span) in branches.reachable {
if attr::cfg_matches(
&cfg,
&ecx.sess,
ecx.current_expansion.lint_node_id,
Some(ecx.ecfg.features),
) {
return Some((tt, arm_span));
}
}
branches.wildcard.map(|(_, tt, span)| (tt, span))
}
pub(super) fn expand_cfg_select<'cx>(
ecx: &'cx mut ExtCtxt<'_>,
sp: Span,
tts: TokenStream,
) -> MacroExpanderResult<'cx> {
ExpandResult::Ready(match parse_cfg_select(&mut ecx.new_parser_from_tts(tts)) {
Ok(branches) => {
if let Some((underscore, _, _)) = branches.wildcard {
// Warn for every unreachable rule. We store the fully parsed branch for rustfmt.
for (rule, _, _) in &branches.unreachable {
let span = match rule {
CfgSelectRule::Wildcard(underscore) => underscore.span,
CfgSelectRule::Cfg(cfg) => cfg.span(),
};
let err = CfgSelectUnreachable { span, wildcard_span: underscore.span };
ecx.dcx().emit_warn(err);
}
}
if let Some((tts, arm_span)) = select_arm(ecx, branches) {
return ExpandResult::from_tts(
ecx,
tts,
sp,
arm_span,
Ident::with_dummy_span(sym::cfg_select),
);
} else {
// Emit a compiler error when none of the rules matched.
let guar = ecx.dcx().emit_err(CfgSelectNoMatches { span: sp });
DummyResult::any(sp, guar)
}
}
Err(err) => {
let guar = err.emit();
DummyResult::any(sp, guar)
}
})
}
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