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Rollup merge of #119766 - oli-obk:split_tait_and_atpit, r=compiler-errors

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Split tait and impl trait in assoc items logic

And simplify the assoc item logic where applicable.

This separation shows that it is easier to reason about impl trait in assoc items compared with TAITs. See https://rust-lang.zulipchat.com/#narrow/stream/315482-t-compiler.2Fetc.2Fopaque-types/topic/impl.20trait.20in.20associated.20type for some discussion.

The current plan is to try to stabilize impl trait in associated items before TAIT, as they do not have any issues with their defining scopes (see https://github.com/rust-lang/rust/issues/107645 for why this is not a trivial or uncontroversial topic).
This commit is contained in:
León Orell Valerian Liehr 2024-01-23 21:53:56 +01:00 • committed by GitHub
commit 5da220a095
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21 changed files with 615 additions and 73 deletions
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6
compiler/rustc_hir_analysis/src/collect/type_of.rs
View file

@ -530,9 +530,13 @@ pub(super) fn type_of_opaque(
Ok(ty::EarlyBinder::bind(match tcx.hir_node_by_def_id(def_id) {
Node::Item(item) => match item.kind {
ItemKind::OpaqueTy(OpaqueTy {
origin: hir::OpaqueTyOrigin::TyAlias { .. },
origin: hir::OpaqueTyOrigin::TyAlias { in_assoc_ty: false },
..
}) => opaque::find_opaque_ty_constraints_for_tait(tcx, def_id),
ItemKind::OpaqueTy(OpaqueTy {
origin: hir::OpaqueTyOrigin::TyAlias { in_assoc_ty: true },
..
}) => opaque::find_opaque_ty_constraints_for_impl_trait_in_assoc_type(tcx, def_id),
// Opaque types desugared from `impl Trait`.
ItemKind::OpaqueTy(&OpaqueTy {
origin:

78
compiler/rustc_hir_analysis/src/collect/type_of/opaque.rs
View file

@ -23,6 +23,60 @@ pub fn test_opaque_hidden_types(tcx: TyCtxt<'_>) -> Result<(), ErrorGuaranteed>
res
}
/// Checks "defining uses" of opaque `impl Trait` in associated types.
/// These can only be defined by associated items of the same trait.
#[instrument(skip(tcx), level = "debug")]
pub(super) fn find_opaque_ty_constraints_for_impl_trait_in_assoc_type(
tcx: TyCtxt<'_>,
def_id: LocalDefId,
) -> Ty<'_> {
let mut parent_def_id = def_id;
while tcx.def_kind(parent_def_id) == def::DefKind::OpaqueTy {
// Account for `type Alias = impl Trait<Foo = impl Trait>;` (#116031)
parent_def_id = tcx.local_parent(parent_def_id);
}
let impl_def_id = tcx.local_parent(parent_def_id);
match tcx.def_kind(impl_def_id) {
DefKind::Impl { .. } => {}
other => bug!("invalid impl trait in assoc type parent: {other:?}"),
}
let mut locator = TaitConstraintLocator { def_id, tcx, found: None, typeck_types: vec![] };
for &assoc_id in tcx.associated_item_def_ids(impl_def_id) {
let assoc = tcx.associated_item(assoc_id);
match assoc.kind {
ty::AssocKind::Const | ty::AssocKind::Fn => {
locator.check(assoc_id.expect_local(), ImplTraitSource::AssocTy)
}
// Associated types don't have bodies, so they can't constrain hidden types
ty::AssocKind::Type => {}
}
}
if let Some(hidden) = locator.found {
// Only check against typeck if we didn't already error
if !hidden.ty.references_error() {
for concrete_type in locator.typeck_types {
if concrete_type.ty != tcx.erase_regions(hidden.ty)
&& !(concrete_type, hidden).references_error()
{
hidden.report_mismatch(&concrete_type, def_id, tcx).emit();
}
}
}
hidden.ty
} else {
let reported = tcx.dcx().emit_err(UnconstrainedOpaqueType {
span: tcx.def_span(def_id),
name: tcx.item_name(parent_def_id.to_def_id()),
what: "impl",
});
Ty::new_error(tcx, reported)
}
}
/// Checks "defining uses" of opaque `impl Trait` types to ensure that they meet the restrictions
/// laid for "higher-order pattern unification".
/// This ensures that inference is tractable.
@ -128,9 +182,15 @@ struct TaitConstraintLocator<'tcx> {
typeck_types: Vec<ty::OpaqueHiddenType<'tcx>>,
}
#[derive(Debug)]
enum ImplTraitSource {
AssocTy,
TyAlias,
}
impl TaitConstraintLocator<'_> {
#[instrument(skip(self), level = "debug")]
fn check(&mut self, item_def_id: LocalDefId) {
fn check(&mut self, item_def_id: LocalDefId, source: ImplTraitSource) {
// Don't try to check items that cannot possibly constrain the type.
if !self.tcx.has_typeck_results(item_def_id) {
debug!("no constraint: no typeck results");
@ -182,7 +242,13 @@ impl TaitConstraintLocator<'_> {
continue;
}
constrained = true;
if !self.tcx.opaque_types_defined_by(item_def_id).contains(&self.def_id) {
let opaque_types_defined_by = match source {
ImplTraitSource::AssocTy => {
self.tcx.impl_trait_in_assoc_types_defined_by(item_def_id)
}
ImplTraitSource::TyAlias => self.tcx.opaque_types_defined_by(item_def_id),
};
if !opaque_types_defined_by.contains(&self.def_id) {
self.tcx.dcx().emit_err(TaitForwardCompat {
span: hidden_type.span,
item_span: self
@ -240,7 +306,7 @@ impl<'tcx> intravisit::Visitor<'tcx> for TaitConstraintLocator<'tcx> {
}
fn visit_expr(&mut self, ex: &'tcx Expr<'tcx>) {
if let hir::ExprKind::Closure(closure) = ex.kind {
self.check(closure.def_id);
self.check(closure.def_id, ImplTraitSource::TyAlias);
}
intravisit::walk_expr(self, ex);
}
@ -248,7 +314,7 @@ impl<'tcx> intravisit::Visitor<'tcx> for TaitConstraintLocator<'tcx> {
trace!(?it.owner_id);
// The opaque type itself or its children are not within its reveal scope.
if it.owner_id.def_id != self.def_id {
self.check(it.owner_id.def_id);
self.check(it.owner_id.def_id, ImplTraitSource::TyAlias);
intravisit::walk_item(self, it);
}
}
@ -256,13 +322,13 @@ impl<'tcx> intravisit::Visitor<'tcx> for TaitConstraintLocator<'tcx> {
trace!(?it.owner_id);
// The opaque type itself or its children are not within its reveal scope.
if it.owner_id.def_id != self.def_id {
self.check(it.owner_id.def_id);
self.check(it.owner_id.def_id, ImplTraitSource::TyAlias);
intravisit::walk_impl_item(self, it);
}
}
fn visit_trait_item(&mut self, it: &'tcx TraitItem<'tcx>) {
trace!(?it.owner_id);
self.check(it.owner_id.def_id);
self.check(it.owner_id.def_id, ImplTraitSource::TyAlias);
intravisit::walk_trait_item(self, it);
}
fn visit_foreign_item(&mut self, it: &'tcx hir::ForeignItem<'tcx>) {