rustc_hir_analysis/variance/
dump.rs

1use std::fmt::Write;
2
3use rustc_hir::def_id::{CRATE_DEF_ID, LocalDefId};
4use rustc_middle::ty::{GenericArgs, TyCtxt};
5use rustc_span::sym;
6
7fn format_variances(tcx: TyCtxt<'_>, def_id: LocalDefId) -> String {
8    let variances = tcx.variances_of(def_id);
9    let generics = GenericArgs::identity_for_item(tcx, def_id);
10    // 7 = 2-letter parameter + ": " + 1-letter variance + ", "
11    let mut ret = String::with_capacity(2 + 7 * variances.len());
12    ret.push('[');
13    for (arg, variance) in generics.iter().zip(variances.iter()) {
14        write!(ret, "{arg}: {variance:?}, ").unwrap();
15    }
16    // Remove trailing `, `.
17    if !variances.is_empty() {
18        ret.pop();
19        ret.pop();
20    }
21    ret.push(']');
22    ret
23}
24
25pub(crate) fn variances(tcx: TyCtxt<'_>) {
26    let crate_items = tcx.hir_crate_items(());
27
28    if tcx.has_attr(CRATE_DEF_ID, sym::rustc_variance_of_opaques) {
29        for id in crate_items.opaques() {
30            tcx.dcx().emit_err(crate::errors::VariancesOf {
31                span: tcx.def_span(id),
32                variances: format_variances(tcx, id),
33            });
34        }
35    }
36
37    for id in crate_items.free_items() {
38        if !tcx.has_attr(id.owner_id, sym::rustc_variance) {
39            continue;
40        }
41
42        tcx.dcx().emit_err(crate::errors::VariancesOf {
43            span: tcx.def_span(id.owner_id),
44            variances: format_variances(tcx, id.owner_id.def_id),
45        });
46    }
47}