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Auto merge of #101679 - compiler-errors:rpitit-default-body, r=nikomatsakis

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Support default-body trait functions with return-position `impl Trait` in traits

Introduce a new `Trait` candidate kind for the `ImplTraitInTrait` projection candidate, which just projects an RPITIT down to its opaque type form.

This is a hack until we lower RPITITs to regular associated types, after which we will need to rework how these default bodies are type-checked, so comments are left in a few places for us to clean up later.

Fixes #101665
This commit is contained in:
bors 2022-10-12 21:03:47 +00:00
commit 0938e1680d
14 changed files with 166 additions and 129 deletions
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62
compiler/rustc_hir_analysis/src/check/check.rs
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@ -522,23 +522,33 @@ fn check_static_inhabited<'tcx>(tcx: TyCtxt<'tcx>, def_id: LocalDefId) {
/// Checks that an opaque type does not contain cycles and does not use `Self` or `T::Foo`
/// projections that would result in "inheriting lifetimes".
pub(super) fn check_opaque<'tcx>(
tcx: TyCtxt<'tcx>,
def_id: LocalDefId,
substs: SubstsRef<'tcx>,
origin: &hir::OpaqueTyOrigin,
) {
let span = tcx.def_span(def_id);
check_opaque_for_inheriting_lifetimes(tcx, def_id, span);
if tcx.type_of(def_id).references_error() {
fn check_opaque<'tcx>(tcx: TyCtxt<'tcx>, id: hir::ItemId) {
let item = tcx.hir().item(id);
let hir::ItemKind::OpaqueTy(hir::OpaqueTy { origin, .. }) = item.kind else {
tcx.sess.delay_span_bug(tcx.hir().span(id.hir_id()), "expected opaque item");
return;
}
if check_opaque_for_cycles(tcx, def_id, substs, span, origin).is_err() {
return;
}
check_opaque_meets_bounds(tcx, def_id, substs, span, origin);
}
};
// HACK(jynelson): trying to infer the type of `impl trait` breaks documenting
// `async-std` (and `pub async fn` in general).
// Since rustdoc doesn't care about the concrete type behind `impl Trait`, just don't look at it!
// See https://github.com/rust-lang/rust/issues/75100
if tcx.sess.opts.actually_rustdoc {
return;
}
let substs = InternalSubsts::identity_for_item(tcx, item.def_id.to_def_id());
let span = tcx.def_span(item.def_id.def_id);
check_opaque_for_inheriting_lifetimes(tcx, item.def_id.def_id, span);
if tcx.type_of(item.def_id.def_id).references_error() {
return;
}
if check_opaque_for_cycles(tcx, item.def_id.def_id, substs, span, &origin).is_err() {
return;
}
check_opaque_meets_bounds(tcx, item.def_id.def_id, substs, span, &origin);
}
/// Checks that an opaque type does not use `Self` or `T::Foo` projections that would result
/// in "inheriting lifetimes".
#[instrument(level = "debug", skip(tcx, span))]
@ -857,17 +867,17 @@ fn check_item_type<'tcx>(tcx: TyCtxt<'tcx>, id: hir::ItemId) {
check_union(tcx, id.def_id.def_id);
}
DefKind::OpaqueTy => {
let item = tcx.hir().item(id);
let hir::ItemKind::OpaqueTy(hir::OpaqueTy { origin, .. }) = item.kind else {
return;
};
// HACK(jynelson): trying to infer the type of `impl trait` breaks documenting
// `async-std` (and `pub async fn` in general).
// Since rustdoc doesn't care about the concrete type behind `impl Trait`, just don't look at it!
// See https://github.com/rust-lang/rust/issues/75100
if !tcx.sess.opts.actually_rustdoc {
let substs = InternalSubsts::identity_for_item(tcx, item.def_id.to_def_id());
check_opaque(tcx, item.def_id.def_id, substs, &origin);
check_opaque(tcx, id);
}
DefKind::ImplTraitPlaceholder => {
let parent = tcx.impl_trait_in_trait_parent(id.def_id.to_def_id());
// Only check the validity of this opaque type if the function has a default body
if let hir::Node::TraitItem(hir::TraitItem {
kind: hir::TraitItemKind::Fn(_, hir::TraitFn::Provided(_)),
..
}) = tcx.hir().get_by_def_id(parent.expect_local())
{
check_opaque(tcx, id);
}
}
DefKind::TyAlias => {