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Auto merge of #112652 - oli-obk:tait_only_in_sig, r=compiler-errors

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Require TAITs to be mentioned in the signatures of functions that register hidden types for them

r? `@lcnr` `@compiler-errors`

This implements the lang team decision from [the TAIT design meeting](https://rust-lang.zulipchat.com/#narrow/stream/213817-t-lang/topic/design.20meeting.202023-05-31.20TAITs/near/362518164).
This commit is contained in:
bors 2023-07-08 03:22:54 +00:00
commit d4096e0412
76 changed files with 783 additions and 191 deletions
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154
compiler/rustc_ty_utils/src/opaque_types.rs
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@ -1,5 +1,7 @@
use rustc_data_structures::fx::FxHashSet;
use rustc_hir::intravisit::Visitor;
use rustc_hir::{def::DefKind, def_id::LocalDefId};
use rustc_hir::{intravisit, CRATE_HIR_ID};
use rustc_middle::query::Providers;
use rustc_middle::ty::util::{CheckRegions, NotUniqueParam};
use rustc_middle::ty::{self, Ty, TyCtxt};
@ -51,7 +53,7 @@ impl<'tcx> OpaqueTypeCollector<'tcx> {
fn parent(&self) -> Option<LocalDefId> {
match self.tcx.def_kind(self.item) {
DefKind::Fn => None,
DefKind::AnonConst | DefKind::InlineConst | DefKind::Fn | DefKind::TyAlias => None,
DefKind::AssocFn | DefKind::AssocTy | DefKind::AssocConst => {
Some(self.tcx.local_parent(self.item))
}
@ -61,6 +63,73 @@ impl<'tcx> OpaqueTypeCollector<'tcx> {
),
}
}
/// Returns `true` if `opaque_hir_id` is a sibling or a child of a sibling of `self.item`.
///
/// Example:
/// ```ignore UNSOLVED (is this a bug?)
/// # #![feature(type_alias_impl_trait)]
/// pub mod foo {
/// pub mod bar {
/// pub trait Bar { /* ... */ }
/// pub type Baz = impl Bar;
///
/// # impl Bar for () {}
/// fn f1() -> Baz { /* ... */ }
/// }
/// fn f2() -> bar::Baz { /* ... */ }
/// }
/// ```
///
/// and `opaque_def_id` is the `DefId` of the definition of the opaque type `Baz`.
/// For the above example, this function returns `true` for `f1` and `false` for `f2`.
#[instrument(level = "trace", skip(self), ret)]
fn check_tait_defining_scope(&self, opaque_def_id: LocalDefId) -> bool {
let mut hir_id = self.tcx.hir().local_def_id_to_hir_id(self.item);
let opaque_hir_id = self.tcx.hir().local_def_id_to_hir_id(opaque_def_id);
// Named opaque types can be defined by any siblings or children of siblings.
let scope = self.tcx.hir().get_defining_scope(opaque_hir_id);
// We walk up the node tree until we hit the root or the scope of the opaque type.
while hir_id != scope && hir_id != CRATE_HIR_ID {
hir_id = self.tcx.hir().get_parent_item(hir_id).into();
}
// Syntactically, we are allowed to define the concrete type if:
hir_id == scope
}
fn collect_body_and_predicate_taits(&mut self) {
// Look at all where bounds.
self.tcx.predicates_of(self.item).instantiate_identity(self.tcx).visit_with(self);
// An item is allowed to constrain opaques declared within its own body (but not nested within
// nested functions).
self.collect_taits_declared_in_body();
}
#[instrument(level = "trace", skip(self))]
fn collect_taits_declared_in_body(&mut self) {
let body = self.tcx.hir().body(self.tcx.hir().body_owned_by(self.item)).value;
struct TaitInBodyFinder<'a, 'tcx> {
collector: &'a mut OpaqueTypeCollector<'tcx>,
}
impl<'v> intravisit::Visitor<'v> for TaitInBodyFinder<'_, '_> {
#[instrument(level = "trace", skip(self))]
fn visit_nested_item(&mut self, id: rustc_hir::ItemId) {
let id = id.owner_id.def_id;
if let DefKind::TyAlias = self.collector.tcx.def_kind(id) {
let items = self.collector.tcx.opaque_types_defined_by(id);
self.collector.opaques.extend(items);
}
}
#[instrument(level = "trace", skip(self))]
// Recurse into these, as they are type checked with their parent
fn visit_nested_body(&mut self, id: rustc_hir::BodyId) {
let body = self.collector.tcx.hir().body(id);
self.visit_body(body);
}
}
TaitInBodyFinder { collector: self }.visit_expr(body);
}
}
impl<'tcx> TypeVisitor<TyCtxt<'tcx>> for OpaqueTypeCollector<'tcx> {
@ -73,6 +142,21 @@ impl<'tcx> TypeVisitor<TyCtxt<'tcx>> for OpaqueTypeCollector<'tcx> {
return ControlFlow::Continue(());
}
// TAITs outside their defining scopes are ignored.
let origin = self.tcx.opaque_type_origin(alias_ty.def_id.expect_local());
trace!(?origin);
match origin {
rustc_hir::OpaqueTyOrigin::FnReturn(_)
| rustc_hir::OpaqueTyOrigin::AsyncFn(_) => {}
rustc_hir::OpaqueTyOrigin::TyAlias { in_assoc_ty } => {
if !in_assoc_ty {
if !self.check_tait_defining_scope(alias_ty.def_id.expect_local()) {
return ControlFlow::Continue(());
}
}
}
}
self.opaques.push(alias_ty.def_id.expect_local());
match self.tcx.uses_unique_generic_params(alias_ty.substs, CheckRegions::Bound) {
@ -188,33 +272,36 @@ impl<'tcx> TypeVisitor<TyCtxt<'tcx>> for OpaqueTypeCollector<'tcx> {
fn opaque_types_defined_by<'tcx>(tcx: TyCtxt<'tcx>, item: LocalDefId) -> &'tcx [LocalDefId] {
let kind = tcx.def_kind(item);
trace!(?kind);
// FIXME(type_alias_impl_trait): This is definitely still wrong except for RPIT and impl trait in assoc types.
let mut collector = OpaqueTypeCollector::new(tcx, item);
match kind {
// We're also doing this for `AssocTy` for the wf checks in `check_opaque_meets_bounds`
DefKind::Fn | DefKind::AssocFn | DefKind::AssocTy | DefKind::AssocConst => {
let mut collector = OpaqueTypeCollector::new(tcx, item);
match kind {
// Walk over the signature of the function-like to find the opaques.
DefKind::AssocFn | DefKind::Fn => {
let ty_sig = tcx.fn_sig(item).subst_identity();
let hir_sig = tcx.hir().get_by_def_id(item).fn_sig().unwrap();
// Walk over the inputs and outputs manually in order to get good spans for them.
collector.visit_spanned(hir_sig.decl.output.span(), ty_sig.output());
for (hir, ty) in hir_sig.decl.inputs.iter().zip(ty_sig.inputs().iter()) {
collector.visit_spanned(hir.span, ty.map_bound(|x| *x));
}
}
// Walk over the type of the item to find opaques.
DefKind::AssocTy | DefKind::AssocConst => {
let span = match tcx.hir().get_by_def_id(item).ty() {
Some(ty) => ty.span,
_ => tcx.def_span(item),
};
collector.visit_spanned(span, tcx.type_of(item).subst_identity());
}
_ => unreachable!(),
// Walk over the signature of the function-like to find the opaques.
DefKind::AssocFn | DefKind::Fn => {
let ty_sig = tcx.fn_sig(item).subst_identity();
let hir_sig = tcx.hir().get_by_def_id(item).fn_sig().unwrap();
// Walk over the inputs and outputs manually in order to get good spans for them.
collector.visit_spanned(hir_sig.decl.output.span(), ty_sig.output());
for (hir, ty) in hir_sig.decl.inputs.iter().zip(ty_sig.inputs().iter()) {
collector.visit_spanned(hir.span, ty.map_bound(|x| *x));
}
collector.collect_body_and_predicate_taits();
}
// Walk over the type of the item to find opaques.
DefKind::Static(_) | DefKind::Const | DefKind::AssocConst | DefKind::AnonConst => {
let span = match tcx.hir().get_by_def_id(item).ty() {
Some(ty) => ty.span,
_ => tcx.def_span(item),
};
collector.visit_spanned(span, tcx.type_of(item).subst_identity());
collector.collect_body_and_predicate_taits();
}
// We're also doing this for `AssocTy` for the wf checks in `check_opaque_meets_bounds`
DefKind::TyAlias | DefKind::AssocTy => {
tcx.type_of(item).subst_identity().visit_with(&mut collector);
}
DefKind::OpaqueTy => {
for (pred, span) in tcx.explicit_item_bounds(item).subst_identity_iter_copied() {
collector.visit_spanned(span, pred);
}
tcx.arena.alloc_from_iter(collector.opaques)
}
DefKind::Mod
| DefKind::Struct
@ -222,31 +309,26 @@ fn opaque_types_defined_by<'tcx>(tcx: TyCtxt<'tcx>, item: LocalDefId) -> &'tcx [
| DefKind::Enum
| DefKind::Variant
| DefKind::Trait
| DefKind::TyAlias
| DefKind::ForeignTy
| DefKind::TraitAlias
| DefKind::TyParam
| DefKind::Const
| DefKind::ConstParam
| DefKind::Static(_)
| DefKind::Ctor(_, _)
| DefKind::Macro(_)
| DefKind::ExternCrate
| DefKind::Use
| DefKind::ForeignMod
| DefKind::AnonConst
| DefKind::InlineConst
| DefKind::OpaqueTy
| DefKind::ImplTraitPlaceholder
| DefKind::Field
| DefKind::LifetimeParam
| DefKind::GlobalAsm
| DefKind::Impl { .. }
| DefKind::Closure
| DefKind::Generator => {
span_bug!(tcx.def_span(item), "{kind:?} is type checked as part of its parent")
| DefKind::Impl { .. } => {}
// Closures and generators are type checked with their parent, so there is no difference here.
DefKind::Closure | DefKind::Generator | DefKind::InlineConst => {
return tcx.opaque_types_defined_by(tcx.local_parent(item));
}
}
tcx.arena.alloc_from_iter(collector.opaques)
}
pub(super) fn provide(providers: &mut Providers) {