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Auto merge of #96964 - oli-obk:const_trait_mvp, r=compiler-errors

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Replace `#[default_method_body_is_const]` with `#[const_trait]`

pulled out of #96077

related issues:  #67792 and #92158

cc `@fee1-dead`

This is groundwork to only allowing `impl const Trait` for traits that are marked with `#[const_trait]`. This is necessary to prevent adding a new default method from becoming a breaking change (as it could be a non-const fn).
This commit is contained in:
bors 2022-05-30 09:19:03 +00:00
commit 5c780b98d1
32 changed files with 82 additions and 260 deletions
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23
compiler/rustc_passes/src/check_attr.rs
View file

@ -122,9 +122,7 @@ impl CheckAttrVisitor<'_> {
| sym::rustc_if_this_changed
| sym::rustc_then_this_would_need => self.check_rustc_dirty_clean(&attr),
sym::cmse_nonsecure_entry => self.check_cmse_nonsecure_entry(attr, span, target),
sym::default_method_body_is_const => {
self.check_default_method_body_is_const(attr, span, target)
}
sym::const_trait => self.check_const_trait(attr, span, target),
sym::must_not_suspend => self.check_must_not_suspend(&attr, span, target),
sym::must_use => self.check_must_use(hir_id, &attr, span, target),
sym::rustc_pass_by_value => self.check_pass_by_value(&attr, span, target),
@ -2097,23 +2095,14 @@ impl CheckAttrVisitor<'_> {
}
}
/// default_method_body_is_const should only be applied to trait methods with default bodies.
fn check_default_method_body_is_const(
&self,
attr: &Attribute,
span: Span,
target: Target,
) -> bool {
/// `#[const_trait]` only applies to traits.
fn check_const_trait(&self, attr: &Attribute, _span: Span, target: Target) -> bool {
match target {
Target::Method(MethodKind::Trait { body: true }) => true,
Target::Trait => true,
_ => {
self.tcx
.sess
.struct_span_err(
attr.span,
"attribute should be applied to a trait method with body",
)
.span_label(span, "not a trait method or missing a body")
.struct_span_err(attr.span, "attribute should be applied to a trait")
.emit();
false
}
@ -2207,6 +2196,8 @@ impl CheckAttrVisitor<'_> {
"attribute `{}` without any lints has no effect",
attr.name_or_empty()
)
} else if attr.name_or_empty() == sym::default_method_body_is_const {
format!("`default_method_body_is_const` has been replaced with `#[const_trait]` on traits")
} else {
return;
};

62
compiler/rustc_passes/src/check_const.rs
View file

@ -13,7 +13,6 @@ use rustc_hir as hir;
use rustc_hir::def_id::LocalDefId;
use rustc_hir::intravisit::{self, Visitor};
use rustc_middle::hir::nested_filter;
use rustc_middle::ty;
use rustc_middle::ty::query::Providers;
use rustc_middle::ty::TyCtxt;
use rustc_session::parse::feature_err;
@ -64,66 +63,6 @@ pub(crate) fn provide(providers: &mut Providers) {
*providers = Providers { check_mod_const_bodies, ..*providers };
}
fn check_item<'tcx>(tcx: TyCtxt<'tcx>, item: &'tcx hir::Item<'tcx>) {
let _: Option<_> = try {
if let hir::ItemKind::Impl(ref imp) = item.kind && let hir::Constness::Const = imp.constness {
let trait_def_id = imp.of_trait.as_ref()?.trait_def_id()?;
let ancestors = tcx
.trait_def(trait_def_id)
.ancestors(tcx, item.def_id.to_def_id())
.ok()?;
let mut to_implement = Vec::new();
for trait_item in tcx.associated_items(trait_def_id).in_definition_order()
{
if let ty::AssocItem {
kind: ty::AssocKind::Fn,
defaultness,
def_id: trait_item_id,
..
} = *trait_item
{
// we can ignore functions that do not have default bodies:
// if those are unimplemented it will be caught by typeck.
if !defaultness.has_value()
|| tcx
.has_attr(trait_item_id, sym::default_method_body_is_const)
{
continue;
}
let is_implemented = ancestors
.leaf_def(tcx, trait_item_id)
.map(|node_item| !node_item.defining_node.is_from_trait())
.unwrap_or(false);
if !is_implemented {
to_implement.push(trait_item_id);
}
}
}
// all nonconst trait functions (not marked with #[default_method_body_is_const])
// must be implemented
if !to_implement.is_empty() {
let not_implemented = to_implement
.into_iter()
.map(|did| tcx.item_name(did).to_string())
.collect::<Vec<_>>()
.join("`, `");
tcx
.sess
.struct_span_err(
item.span,
"const trait implementations may not use non-const default functions",
)
.note(&format!("`{}` not implemented", not_implemented))
.emit();
}
}
};
}
#[derive(Copy, Clone)]
struct CheckConstVisitor<'tcx> {
tcx: TyCtxt<'tcx>,
@ -254,7 +193,6 @@ impl<'tcx> Visitor<'tcx> for CheckConstVisitor<'tcx> {
fn visit_item(&mut self, item: &'tcx hir::Item<'tcx>) {
intravisit::walk_item(self, item);
check_item(self.tcx, item);
}
fn visit_anon_const(&mut self, anon: &'tcx hir::AnonConst) {