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Add #[default_method_body_is_const]

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This commit is contained in:
Deadbeef 2021-07-04 12:24:20 +08:00
parent a84d1b21ae
commit 2db927d8d8
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5 changed files with 82 additions and 22 deletions
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49
compiler/rustc_passes/src/check_const.rs
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@ -8,6 +8,7 @@
//! through, but errors for structured control flow in a `const` should be emitted here.
use rustc_attr as attr;
use rustc_data_structures::stable_set::FxHashSet;
use rustc_errors::struct_span_err;
use rustc_hir as hir;
use rustc_hir::def_id::LocalDefId;
@ -85,34 +86,46 @@ impl<'tcx> hir::itemlikevisit::ItemLikeVisitor<'tcx> for CheckConstTraitVisitor<
if let hir::ItemKind::Impl(ref imp) = item.kind {
if let hir::Constness::Const = imp.constness {
let did = imp.of_trait.as_ref()?.trait_def_id()?;
let trait_fn_cnt = self
.tcx
.associated_item_def_ids(did)
.iter()
.filter(|did| {
matches!(
self.tcx.associated_item(**did),
ty::AssocItem { kind: ty::AssocKind::Fn, .. }
)
})
.count();
let mut to_implement = FxHashSet::default();
let impl_fn_cnt = imp
for did in self.tcx.associated_item_def_ids(did) {
if let ty::AssocItem {
kind: ty::AssocKind::Fn, ident, defaultness, ..
} = self.tcx.associated_item(*did)
{
match (
self.tcx.has_attr(*did, sym::default_method_body_is_const),
defaultness.has_value(),
) {
(false, true) => {
to_implement.insert(ident);
}
// ignore functions that do not have default bodies
// if those are unimplemented it will be catched by
// typeck.
_ => {}
}
}
}
for it in imp
.items
.iter()
.filter(|it| matches!(it.kind, hir::AssocItemKind::Fn { .. }))
.count();
{
to_implement.remove(&it.ident);
}
// number of trait functions unequal to functions in impl,
// meaning that one or more provided/default functions of the
// trait are used.
if trait_fn_cnt != impl_fn_cnt {
// all nonconst trait functions (not marked with #[default_method_body_is_const])
// must be implemented
if !to_implement.is_empty() {
self.tcx
.sess
.struct_span_err(
item.span,
"const trait implementations may not use default functions",
"const trait implementations may not use non-const default functions",
)
.note(&format!("`{}` not implemented", to_implement.into_iter().map(|id| id.to_string()).collect::<Vec<_>>().join("`, `")))
.emit();
}
}