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use std::fmt::Write;
use rustc_hir::def_id::{CRATE_DEF_ID, LocalDefId};
use rustc_middle::ty::{GenericArgs, TyCtxt};
use rustc_span::symbol::sym;
fn format_variances(tcx: TyCtxt<'_>, def_id: LocalDefId) -> String {
let variances = tcx.variances_of(def_id);
let generics = GenericArgs::identity_for_item(tcx, def_id);
// 7 = 2-letter parameter + ": " + 1-letter variance + ", "
let mut ret = String::with_capacity(2 + 7 * variances.len());
ret.push('[');
for (arg, variance) in generics.iter().zip(variances.iter()) {
write!(ret, "{arg}: {variance:?}, ").unwrap();
}
// Remove trailing `, `.
if !variances.is_empty() {
ret.pop();
ret.pop();
}
ret.push(']');
ret
}
pub(crate) fn variances(tcx: TyCtxt<'_>) {
let crate_items = tcx.hir_crate_items(());
if tcx.has_attr(CRATE_DEF_ID, sym::rustc_variance_of_opaques) {
for id in crate_items.opaques() {
tcx.dcx().emit_err(crate::errors::VariancesOf {
span: tcx.def_span(id),
variances: format_variances(tcx, id),
});
}
}
for id in crate_items.free_items() {
if !tcx.has_attr(id.owner_id, sym::rustc_variance) {
continue;
}
tcx.dcx().emit_err(crate::errors::VariancesOf {
span: tcx.def_span(id.owner_id),
variances: format_variances(tcx, id.owner_id.def_id),
});
}
}
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