Rewrite representability
This commit is contained in:
Cameron Steffen
parent
e42c4d7218
commit
ff940db666
61 changed files with 537 additions and 744 deletions
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@ -1,386 +1,119 @@
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//! Check whether a type is representable.
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use rustc_data_structures::fx::FxHashMap;
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use rustc_hir as hir;
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use rustc_middle::ty::{self, Ty, TyCtxt};
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use rustc_span::Span;
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use std::cmp;
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#![allow(rustc::untranslatable_diagnostic, rustc::diagnostic_outside_of_impl)]
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/// Describes whether a type is representable. For types that are not
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/// representable, 'SelfRecursive' and 'ContainsRecursive' are used to
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/// distinguish between types that are recursive with themselves and types that
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/// contain a different recursive type. These cases can therefore be treated
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/// differently when reporting errors.
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///
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/// The ordering of the cases is significant. They are sorted so that cmp::max
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/// will keep the "more erroneous" of two values.
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#[derive(Clone, PartialOrd, Ord, Eq, PartialEq, Debug)]
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pub enum Representability {
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Representable,
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ContainsRecursive,
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/// Return a list of types that are included in themselves:
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/// the spans where they are self-included, and (if found)
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/// the HirId of the FieldDef that defines the self-inclusion.
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SelfRecursive(Vec<(Span, Option<hir::HirId>)>),
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use rustc_hir::def::DefKind;
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use rustc_index::bit_set::BitSet;
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use rustc_middle::ty::query::Providers;
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use rustc_middle::ty::{self, Representability, Ty, TyCtxt};
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use rustc_span::def_id::{DefId, LocalDefId};
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pub fn provide(providers: &mut Providers) {
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*providers =
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Providers { representability, representability_adt_ty, params_in_repr, ..*providers };
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}
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/// Check whether a type is representable. This means it cannot contain unboxed
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/// structural recursion. This check is needed for structs and enums.
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pub fn ty_is_representable<'tcx>(
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tcx: TyCtxt<'tcx>,
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ty: Ty<'tcx>,
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sp: Span,
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field_id: Option<hir::HirId>,
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) -> Representability {
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debug!("is_type_representable: {:?}", ty);
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// To avoid a stack overflow when checking an enum variant or struct that
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// contains a different, structurally recursive type, maintain a stack of
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// seen types and check recursion for each of them (issues #3008, #3779,
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// #74224, #84611). `shadow_seen` contains the full stack and `seen` only
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// the one for the current type (e.g. if we have structs A and B, B contains
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// a field of type A, and we're currently looking at B, then `seen` will be
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// cleared when recursing to check A, but `shadow_seen` won't, so that we
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// can catch cases of mutual recursion where A also contains B).
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let mut seen: Vec<Ty<'_>> = Vec::new();
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let mut shadow_seen: Vec<ty::AdtDef<'tcx>> = Vec::new();
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let mut representable_cache = FxHashMap::default();
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let mut force_result = false;
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let r = is_type_structurally_recursive(
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tcx,
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&mut seen,
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&mut shadow_seen,
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&mut representable_cache,
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ty,
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sp,
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field_id,
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&mut force_result,
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);
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debug!("is_type_representable: {:?} is {:?}", ty, r);
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r
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}
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// Iterate until something non-representable is found
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fn fold_repr<It: Iterator<Item = Representability>>(iter: It) -> Representability {
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iter.fold(Representability::Representable, |r1, r2| match (r1, r2) {
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(Representability::SelfRecursive(v1), Representability::SelfRecursive(v2)) => {
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Representability::SelfRecursive(v1.into_iter().chain(v2).collect())
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macro_rules! rtry {
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($e:expr) => {
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match $e {
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e @ Representability::Infinite => return e,
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Representability::Representable => {}
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}
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(r1, r2) => cmp::max(r1, r2),
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})
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};
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}
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fn are_inner_types_recursive<'tcx>(
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tcx: TyCtxt<'tcx>,
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seen: &mut Vec<Ty<'tcx>>,
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shadow_seen: &mut Vec<ty::AdtDef<'tcx>>,
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representable_cache: &mut FxHashMap<Ty<'tcx>, Representability>,
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ty: Ty<'tcx>,
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sp: Span,
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field_id: Option<hir::HirId>,
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force_result: &mut bool,
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) -> Representability {
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debug!("are_inner_types_recursive({:?}, {:?}, {:?})", ty, seen, shadow_seen);
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match ty.kind() {
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ty::Tuple(fields) => {
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// Find non representable
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fold_repr(fields.iter().map(|ty| {
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is_type_structurally_recursive(
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tcx,
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seen,
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shadow_seen,
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representable_cache,
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ty,
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sp,
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field_id,
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force_result,
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)
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}))
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}
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// Fixed-length vectors.
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// FIXME(#11924) Behavior undecided for zero-length vectors.
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ty::Array(ty, _) => is_type_structurally_recursive(
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tcx,
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seen,
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shadow_seen,
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representable_cache,
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*ty,
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sp,
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field_id,
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force_result,
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),
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ty::Adt(def, substs) => {
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// Find non representable fields with their spans
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fold_repr(def.all_fields().map(|field| {
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let ty = field.ty(tcx, substs);
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let (sp, field_id) = match field
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.did
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.as_local()
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.map(|id| tcx.hir().local_def_id_to_hir_id(id))
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.and_then(|id| tcx.hir().find(id))
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{
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Some(hir::Node::Field(field)) => (field.ty.span, Some(field.hir_id)),
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_ => (sp, field_id),
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};
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let mut result = None;
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// First, we check whether the field type per se is representable.
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// This catches cases as in #74224 and #84611. There is a special
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// case related to mutual recursion, though; consider this example:
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//
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// struct A<T> {
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// z: T,
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// x: B<T>,
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// }
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//
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// struct B<T> {
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// y: A<T>
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// }
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//
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// Here, without the following special case, both A and B are
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// ContainsRecursive, which is a problem because we only report
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// errors for SelfRecursive. We fix this by detecting this special
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// case (shadow_seen.first() is the type we are originally
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// interested in, and if we ever encounter the same AdtDef again,
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// we know that it must be SelfRecursive) and "forcibly" returning
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// SelfRecursive (by setting force_result, which tells the calling
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// invocations of are_inner_types_representable to forward the
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// result without adjusting).
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if shadow_seen.len() > seen.len() && shadow_seen.first() == Some(def) {
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*force_result = true;
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result = Some(Representability::SelfRecursive(vec![(sp, field_id)]));
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fn representability(tcx: TyCtxt<'_>, def_id: LocalDefId) -> Representability {
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match tcx.def_kind(def_id) {
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DefKind::Struct | DefKind::Union | DefKind::Enum => {
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let adt_def = tcx.adt_def(def_id);
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for variant in adt_def.variants() {
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for field in variant.fields.iter() {
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rtry!(tcx.representability(field.did.expect_local()));
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}
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if result == None {
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result = Some(Representability::Representable);
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// Now, we check whether the field types per se are representable, e.g.
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// for struct Foo { x: Option<Foo> }, we first check whether Option<_>
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// by itself is representable (which it is), and the nesting of Foo
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// will be detected later. This is necessary for #74224 and #84611.
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// If we have encountered an ADT definition that we have not seen
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// before (no need to check them twice), recurse to see whether that
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// definition is SelfRecursive. If so, we must be ContainsRecursive.
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if shadow_seen.len() > 1
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&& !shadow_seen
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.iter()
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.take(shadow_seen.len() - 1)
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.any(|seen_def| seen_def == def)
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{
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let adt_def_id = def.did();
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let raw_adt_ty = tcx.type_of(adt_def_id);
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debug!("are_inner_types_recursive: checking nested type: {:?}", raw_adt_ty);
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// Check independently whether the ADT is SelfRecursive. If so,
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// we must be ContainsRecursive (except for the special case
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// mentioned above).
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let mut nested_seen: Vec<Ty<'_>> = vec![];
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result = Some(
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match is_type_structurally_recursive(
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tcx,
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&mut nested_seen,
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shadow_seen,
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representable_cache,
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raw_adt_ty,
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sp,
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field_id,
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force_result,
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) {
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Representability::SelfRecursive(_) => {
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if *force_result {
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Representability::SelfRecursive(vec![(sp, field_id)])
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} else {
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Representability::ContainsRecursive
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}
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}
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x => x,
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},
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);
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}
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// We only enter the following block if the type looks representable
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// so far. This is necessary for cases such as this one (#74224):
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//
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// struct A<T> {
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// x: T,
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// y: A<A<T>>,
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// }
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//
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// struct B {
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// z: A<usize>
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// }
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//
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// When checking B, we recurse into A and check field y of type
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// A<A<usize>>. We haven't seen this exact type before, so we recurse
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// into A<A<usize>>, which contains, A<A<A<usize>>>, and so forth,
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// ad infinitum. We can prevent this from happening by first checking
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// A separately (the code above) and only checking for nested Bs if
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// A actually looks representable (which it wouldn't in this example).
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if result == Some(Representability::Representable) {
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// Now, even if the type is representable (e.g. Option<_>),
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// it might still contribute to a recursive type, e.g.:
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// struct Foo { x: Option<Option<Foo>> }
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// These cases are handled by passing the full `seen`
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// stack to is_type_structurally_recursive (instead of the
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// empty `nested_seen` above):
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result = Some(
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match is_type_structurally_recursive(
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tcx,
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seen,
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shadow_seen,
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representable_cache,
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ty,
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sp,
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field_id,
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force_result,
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) {
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Representability::SelfRecursive(_) => {
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Representability::SelfRecursive(vec![(sp, field_id)])
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}
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x => x,
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},
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);
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}
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}
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result.unwrap()
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}))
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}
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Representability::Representable
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}
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ty::Closure(..) => {
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// this check is run on type definitions, so we don't expect
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// to see closure types
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bug!("requires check invoked on inapplicable type: {:?}", ty)
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DefKind::Field => representability_ty(tcx, tcx.type_of(def_id)),
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def_kind => bug!("unexpected {def_kind:?}"),
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}
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}
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fn representability_ty<'tcx>(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>) -> Representability {
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match *ty.kind() {
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ty::Adt(..) => tcx.representability_adt_ty(ty),
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// FIXME(#11924) allow zero-length arrays?
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ty::Array(ty, _) => representability_ty(tcx, ty),
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ty::Tuple(tys) => {
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for ty in tys {
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rtry!(representability_ty(tcx, ty));
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}
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Representability::Representable
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}
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_ => Representability::Representable,
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}
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}
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fn same_adt<'tcx>(ty: Ty<'tcx>, def: ty::AdtDef<'tcx>) -> bool {
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/*
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The reason for this being a separate query is very subtle:
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Consider this infinitely sized struct: `struct Foo(Box<Foo>, Bar<Foo>)`:
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When calling representability(Foo), a query cycle will occur:
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representability(Foo)
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-> representability_adt_ty(Bar<Foo>)
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-> representability(Foo)
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For the diagnostic output (in `Value::from_cycle_error`), we want to detect that
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the `Foo` in the *second* field of the struct is culpable. This requires
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traversing the HIR of the struct and calling `params_in_repr(Bar)`. But we can't
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call params_in_repr for a given type unless it is known to be representable.
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params_in_repr will cycle/panic on infinitely sized types. Looking at the query
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cycle above, we know that `Bar` is representable because
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representability_adt_ty(Bar<..>) is in the cycle and representability(Bar) is
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*not* in the cycle.
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*/
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fn representability_adt_ty<'tcx>(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>) -> Representability {
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let ty::Adt(adt, substs) = ty.kind() else { bug!("expected adt") };
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if let Some(def_id) = adt.did().as_local() {
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rtry!(tcx.representability(def_id));
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}
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// At this point, we know that the item of the ADT type is representable;
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// but the type parameters may cause a cycle with an upstream type
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let params_in_repr = tcx.params_in_repr(adt.did());
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for (i, subst) in substs.iter().enumerate() {
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if let ty::GenericArgKind::Type(ty) = subst.unpack() {
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if params_in_repr.contains(i as u32) {
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rtry!(representability_ty(tcx, ty));
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}
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}
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}
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Representability::Representable
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}
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fn params_in_repr(tcx: TyCtxt<'_>, def_id: DefId) -> BitSet<u32> {
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let adt_def = tcx.adt_def(def_id);
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let generics = tcx.generics_of(def_id);
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let mut params_in_repr = BitSet::new_empty(generics.params.len());
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for variant in adt_def.variants() {
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for field in variant.fields.iter() {
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params_in_repr_ty(tcx, tcx.type_of(field.did), &mut params_in_repr);
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}
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}
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params_in_repr
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}
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fn params_in_repr_ty<'tcx>(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>, params_in_repr: &mut BitSet<u32>) {
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match *ty.kind() {
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ty::Adt(ty_def, _) => ty_def == def,
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_ => false,
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}
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}
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// Does the type `ty` directly (without indirection through a pointer)
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// contain any types on stack `seen`?
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fn is_type_structurally_recursive<'tcx>(
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tcx: TyCtxt<'tcx>,
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seen: &mut Vec<Ty<'tcx>>,
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shadow_seen: &mut Vec<ty::AdtDef<'tcx>>,
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representable_cache: &mut FxHashMap<Ty<'tcx>, Representability>,
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ty: Ty<'tcx>,
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sp: Span,
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field_id: Option<hir::HirId>,
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force_result: &mut bool,
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) -> Representability {
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debug!("is_type_structurally_recursive: {:?} {:?} {:?}", ty, sp, field_id);
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if let Some(representability) = representable_cache.get(&ty) {
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debug!(
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"is_type_structurally_recursive: {:?} {:?} {:?} - (cached) {:?}",
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ty, sp, field_id, representability
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);
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return representability.clone();
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}
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let representability = is_type_structurally_recursive_inner(
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tcx,
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seen,
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shadow_seen,
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representable_cache,
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ty,
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sp,
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field_id,
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force_result,
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);
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representable_cache.insert(ty, representability.clone());
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representability
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}
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fn is_type_structurally_recursive_inner<'tcx>(
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tcx: TyCtxt<'tcx>,
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seen: &mut Vec<Ty<'tcx>>,
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shadow_seen: &mut Vec<ty::AdtDef<'tcx>>,
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representable_cache: &mut FxHashMap<Ty<'tcx>, Representability>,
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ty: Ty<'tcx>,
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sp: Span,
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field_id: Option<hir::HirId>,
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force_result: &mut bool,
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) -> Representability {
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match ty.kind() {
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ty::Adt(def, _) => {
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{
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debug!("is_type_structurally_recursive_inner: adt: {:?}, seen: {:?}", ty, seen);
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// Iterate through stack of previously seen types.
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let mut iter = seen.iter();
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// The first item in `seen` is the type we are actually curious about.
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// We want to return SelfRecursive if this type contains itself.
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// It is important that we DON'T take generic parameters into account
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// for this check, so that Bar<T> in this example counts as SelfRecursive:
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//
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// struct Foo;
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// struct Bar<T> { x: Bar<Foo> }
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if let Some(&seen_adt) = iter.next() {
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if same_adt(seen_adt, *def) {
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debug!("SelfRecursive: {:?} contains {:?}", seen_adt, ty);
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return Representability::SelfRecursive(vec![(sp, field_id)]);
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}
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}
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// We also need to know whether the first item contains other types
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// that are structurally recursive. If we don't catch this case, we
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// will recurse infinitely for some inputs.
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//
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// It is important that we DO take generic parameters into account
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// here, because nesting e.g. Options is allowed (as long as the
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// definition of Option doesn't itself include an Option field, which
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// would be a case of SelfRecursive above). The following, too, counts
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// as SelfRecursive:
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//
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// struct Foo { Option<Option<Foo>> }
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for &seen_adt in iter {
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if ty == seen_adt {
|
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debug!("ContainsRecursive: {:?} contains {:?}", seen_adt, ty);
|
||||
return Representability::ContainsRecursive;
|
||||
ty::Adt(adt, substs) => {
|
||||
let inner_params_in_repr = tcx.params_in_repr(adt.did());
|
||||
for (i, subst) in substs.iter().enumerate() {
|
||||
if let ty::GenericArgKind::Type(ty) = subst.unpack() {
|
||||
if inner_params_in_repr.contains(i as u32) {
|
||||
params_in_repr_ty(tcx, ty, params_in_repr);
|
||||
}
|
||||
}
|
||||
}
|
||||
|
||||
// For structs and enums, track all previously seen types by pushing them
|
||||
// onto the 'seen' stack.
|
||||
seen.push(ty);
|
||||
shadow_seen.push(*def);
|
||||
let out = are_inner_types_recursive(
|
||||
tcx,
|
||||
seen,
|
||||
shadow_seen,
|
||||
representable_cache,
|
||||
ty,
|
||||
sp,
|
||||
field_id,
|
||||
force_result,
|
||||
);
|
||||
shadow_seen.pop();
|
||||
seen.pop();
|
||||
out
|
||||
}
|
||||
_ => {
|
||||
// No need to push in other cases.
|
||||
are_inner_types_recursive(
|
||||
tcx,
|
||||
seen,
|
||||
shadow_seen,
|
||||
representable_cache,
|
||||
ty,
|
||||
sp,
|
||||
field_id,
|
||||
force_result,
|
||||
)
|
||||
ty::Array(ty, _) => params_in_repr_ty(tcx, ty, params_in_repr),
|
||||
ty::Tuple(tys) => tys.iter().for_each(|ty| params_in_repr_ty(tcx, ty, params_in_repr)),
|
||||
ty::Param(param) => {
|
||||
params_in_repr.insert(param.index);
|
||||
}
|
||||
_ => {}
|
||||
}
|
||||
}
|
||||
|
|
|
|||
Loading…
Add table
Add a link
Reference in a new issue