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Const drop selection candidates

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Deadbeef 2021-09-01 16:34:28 +00:00
parent 894ce921a0
commit a13b13ff46
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GPG key ID: 027DF9338862ADDD
9 changed files with 212 additions and 25 deletions
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15
compiler/rustc_middle/src/traits/mod.rs
View file

@ -529,6 +529,9 @@ pub enum ImplSource<'tcx, N> {
/// ImplSource for a trait alias.
TraitAlias(ImplSourceTraitAliasData<'tcx, N>),
/// ImplSource for a `const Drop` implementation.
ConstDrop(ImplSourceConstDropData),
}
impl<'tcx, N> ImplSource<'tcx, N> {
@ -543,7 +546,8 @@ impl<'tcx, N> ImplSource<'tcx, N> {
ImplSource::Object(d) => d.nested,
ImplSource::FnPointer(d) => d.nested,
ImplSource::DiscriminantKind(ImplSourceDiscriminantKindData)
| ImplSource::Pointee(ImplSourcePointeeData) => Vec::new(),
| ImplSource::Pointee(ImplSourcePointeeData)
| ImplSource::ConstDrop(ImplSourceConstDropData) => Vec::new(),
ImplSource::TraitAlias(d) => d.nested,
ImplSource::TraitUpcasting(d) => d.nested,
}
@ -560,7 +564,8 @@ impl<'tcx, N> ImplSource<'tcx, N> {
ImplSource::Object(d) => &d.nested[..],
ImplSource::FnPointer(d) => &d.nested[..],
ImplSource::DiscriminantKind(ImplSourceDiscriminantKindData)
| ImplSource::Pointee(ImplSourcePointeeData) => &[],
| ImplSource::Pointee(ImplSourcePointeeData)
| ImplSource::ConstDrop(ImplSourceConstDropData) => &[],
ImplSource::TraitAlias(d) => &d.nested[..],
ImplSource::TraitUpcasting(d) => &d.nested[..],
}
@ -621,6 +626,9 @@ impl<'tcx, N> ImplSource<'tcx, N> {
nested: d.nested.into_iter().map(f).collect(),
})
}
ImplSource::ConstDrop(ImplSourceConstDropData) => {
ImplSource::ConstDrop(ImplSourceConstDropData)
}
}
}
}
@ -712,6 +720,9 @@ pub struct ImplSourceDiscriminantKindData;
#[derive(Clone, Debug, PartialEq, Eq, TyEncodable, TyDecodable, HashStable)]
pub struct ImplSourcePointeeData;
#[derive(Clone, Debug, PartialEq, Eq, TyEncodable, TyDecodable, HashStable)]
pub struct ImplSourceConstDropData;
#[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, TypeFoldable, Lift)]
pub struct ImplSourceTraitAliasData<'tcx, N> {
pub alias_def_id: DefId,

3
compiler/rustc_middle/src/traits/select.rs
View file

@ -143,6 +143,9 @@ pub enum SelectionCandidate<'tcx> {
BuiltinObjectCandidate,
BuiltinUnsizeCandidate,
/// Implementation of `const Drop`.
ConstDropCandidate,
}
/// The result of trait evaluation. The order is important

3
compiler/rustc_middle/src/traits/structural_impls.rs
View file

@ -32,6 +32,8 @@ impl<'tcx, N: fmt::Debug> fmt::Debug for traits::ImplSource<'tcx, N> {
super::ImplSource::TraitAlias(ref d) => write!(f, "{:?}", d),
super::ImplSource::TraitUpcasting(ref d) => write!(f, "{:?}", d),
super::ImplSource::ConstDrop(ref d) => write!(f, "{:?}", d),
}
}
}
@ -125,4 +127,5 @@ TrivialTypeFoldableAndLiftImpls! {
super::IfExpressionCause,
super::ImplSourceDiscriminantKindData,
super::ImplSourcePointeeData,
super::ImplSourceConstDropData,
}

6
compiler/rustc_trait_selection/src/traits/project.rs
View file

@ -1477,7 +1477,8 @@ fn assemble_candidates_from_impls<'cx, 'tcx>(
}
super::ImplSource::AutoImpl(..)
| super::ImplSource::Builtin(..)
| super::ImplSource::TraitUpcasting(_) => {
| super::ImplSource::TraitUpcasting(_)
| super::ImplSource::ConstDrop(_) => {
// These traits have no associated types.
selcx.tcx().sess.delay_span_bug(
obligation.cause.span,
@ -1549,7 +1550,8 @@ fn confirm_select_candidate<'cx, 'tcx>(
| super::ImplSource::Param(..)
| super::ImplSource::Builtin(..)
| super::ImplSource::TraitUpcasting(_)
| super::ImplSource::TraitAlias(..) => {
| super::ImplSource::TraitAlias(..)
| super::ImplSource::ConstDrop(_) => {
// we don't create Select candidates with this kind of resolution
span_bug!(
obligation.cause.span,

110
compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs
View file

@ -8,7 +8,7 @@
use rustc_hir as hir;
use rustc_infer::traits::{Obligation, SelectionError, TraitObligation};
use rustc_middle::ty::print::with_no_trimmed_paths;
use rustc_middle::ty::{self, TypeFoldable};
use rustc_middle::ty::{self, Ty, TypeFoldable};
use rustc_target::spec::abi::Abi;
use crate::traits::coherence::Conflict;
@ -277,6 +277,15 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
self.assemble_builtin_bound_candidates(sized_conditions, &mut candidates);
} else if lang_items.unsize_trait() == Some(def_id) {
self.assemble_candidates_for_unsizing(obligation, &mut candidates);
} else if lang_items.drop_trait() == Some(def_id)
&& obligation.predicate.skip_binder().constness == ty::BoundConstness::ConstIfConst
{
if self.is_in_const_context {
self.assemble_const_drop_candidates(obligation, &mut candidates)?;
} else {
// `~const Drop` when we are not in a const context has no effect.
candidates.vec.push(ConstDropCandidate)
}
} else {
if lang_items.clone_trait() == Some(def_id) {
// Same builtin conditions as `Copy`, i.e., every type which has builtin support
@ -803,4 +812,103 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
}
}
}
fn assemble_const_drop_candidates(
&mut self,
obligation: &TraitObligation<'tcx>,
candidates: &mut SelectionCandidateSet<'tcx>,
) -> Result<(), SelectionError<'tcx>> {
let mut stack: Vec<(Ty<'tcx>, usize)> = vec![(obligation.self_ty().skip_binder(), 0)];
while let Some((ty, depth)) = stack.pop() {
self.check_recursion_depth(depth, obligation)?;
let mut copy_candidates = SelectionCandidateSet { vec: Vec::new(), ambiguous: false };
let mut copy_obligation =
obligation.with(obligation.predicate.rebind(ty::TraitPredicate {
trait_ref: ty::TraitRef {
def_id: self.tcx().require_lang_item(hir::LangItem::Copy, None),
substs: self.tcx().mk_substs_trait(ty, &[]),
},
constness: ty::BoundConstness::NotConst,
}));
copy_obligation.recursion_depth = depth + 1;
self.assemble_candidates_from_impls(&copy_obligation, &mut copy_candidates);
let copy_conditions = self.copy_clone_conditions(&copy_obligation);
self.assemble_builtin_bound_candidates(copy_conditions, &mut copy_candidates);
if !copy_candidates.vec.is_empty() {
continue;
}
match ty.kind() {
ty::Int(_)
| ty::Uint(_)
| ty::Float(_)
| ty::Infer(ty::IntVar(_))
| ty::Infer(ty::FloatVar(_))
| ty::FnPtr(_)
| ty::Never
| ty::Ref(..)
| ty::FnDef(..)
| ty::RawPtr(_)
| ty::Bool
| ty::Char
| ty::Str
| ty::Foreign(_) => {} // Do nothing. These types satisfy `const Drop`.
ty::Adt(def, subst) => {
let mut set = SelectionCandidateSet { vec: Vec::new(), ambiguous: false };
self.assemble_candidates_from_impls(obligation, &mut set);
if set
.vec
.into_iter()
.find(|candidate| {
if let SelectionCandidate::ImplCandidate(did) = candidate {
matches!(self.tcx().impl_constness(*did), hir::Constness::NotConst)
} else {
false
}
})
.is_none()
{
// could not find a const impl for Drop, iterate over its fields.
stack
.extend(def.all_fields().map(|f| (f.ty(self.tcx(), subst), depth + 1)));
}
}
ty::Array(ty, _) => stack.push((ty, depth + 1)),
ty::Tuple(_) => stack.extend(ty.tuple_fields().map(|t| (t, depth + 1))),
ty::Closure(_, substs) => {
stack.extend(substs.as_closure().upvar_tys().map(|t| (t, depth + 1)))
}
ty::Generator(_, substs, _) => {
let substs = substs.as_generator();
stack.extend(substs.upvar_tys().map(|t| (t, depth + 1)));
stack.push((substs.witness(), depth + 1));
}
ty::GeneratorWitness(tys) => stack.extend(
self.tcx().erase_late_bound_regions(*tys).iter().map(|t| (t, depth + 1)),
),
ty::Slice(ty) => stack.push((ty, depth + 1)),
ty::Opaque(..)
| ty::Dynamic(..)
| ty::Error(_)
| ty::Bound(..)
| ty::Infer(_)
| ty::Placeholder(_)
| ty::Projection(..)
| ty::Param(..) => return Ok(()),
}
}
// all types have passed.
candidates.vec.push(ConstDropCandidate);
Ok(())
}
}

4
compiler/rustc_trait_selection/src/traits/select/confirmation.rs
View file

@ -28,7 +28,7 @@ use crate::traits::TraitNotObjectSafe;
use crate::traits::VtblSegment;
use crate::traits::{BuiltinDerivedObligation, ImplDerivedObligation};
use crate::traits::{
ImplSourceAutoImplData, ImplSourceBuiltinData, ImplSourceClosureData,
ImplSourceAutoImplData, ImplSourceBuiltinData, ImplSourceClosureData, ImplSourceConstDropData,
ImplSourceDiscriminantKindData, ImplSourceFnPointerData, ImplSourceGeneratorData,
ImplSourceObjectData, ImplSourcePointeeData, ImplSourceTraitAliasData,
ImplSourceTraitUpcastingData, ImplSourceUserDefinedData,
@ -124,6 +124,8 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
let data = self.confirm_trait_upcasting_unsize_candidate(obligation, idx)?;
Ok(ImplSource::TraitUpcasting(data))
}
ConstDropCandidate => Ok(ImplSource::ConstDrop(ImplSourceConstDropData)),
}
}

42
compiler/rustc_trait_selection/src/traits/select/mod.rs
View file

@ -1038,6 +1038,24 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
it.for_each(|o| o.recursion_depth = cmp::max(min_depth, o.recursion_depth) + 1);
}
fn check_recursion_depth<T: Display + TypeFoldable<'tcx>>(
&self,
depth: usize,
error_obligation: &Obligation<'tcx, T>,
) -> Result<(), OverflowError> {
if !self.infcx.tcx.recursion_limit().value_within_limit(depth) {
match self.query_mode {
TraitQueryMode::Standard => {
self.infcx.report_overflow_error(error_obligation, true);
}
TraitQueryMode::Canonical => {
return Err(OverflowError);
}
}
}
Ok(())
}
/// Checks that the recursion limit has not been exceeded.
///
/// The weird return type of this function allows it to be used with the `try` (`?`)
@ -1047,17 +1065,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
obligation: &Obligation<'tcx, T>,
error_obligation: &Obligation<'tcx, V>,
) -> Result<(), OverflowError> {
if !self.infcx.tcx.recursion_limit().value_within_limit(obligation.recursion_depth) {
match self.query_mode {
TraitQueryMode::Standard => {
self.infcx().report_overflow_error(error_obligation, true);
}
TraitQueryMode::Canonical => {
return Err(OverflowError);
}
}
}
Ok(())
self.check_recursion_depth(obligation.recursion_depth, error_obligation)
}
fn in_task<OP, R>(&mut self, op: OP) -> (R, DepNodeIndex)
@ -1079,10 +1087,6 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
let tcx = self.tcx();
// Respect const trait obligations
if self.is_trait_predicate_const(obligation.predicate.skip_binder()) {
if Some(obligation.predicate.skip_binder().trait_ref.def_id)
!= tcx.lang_items().sized_trait()
// const Sized bounds are skipped
{
match candidate {
// const impl
ImplCandidate(def_id)
@ -1097,12 +1101,12 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
// generator, this will raise error in other places
// or ignore error with const_async_blocks feature
GeneratorCandidate => {}
ConstDropCandidate => {}
_ => {
// reject all other types of candidates
return Err(Unimplemented);
}
}
}
}
// Treat negative impls as unimplemented, and reservation impls as ambiguity.
if let ImplCandidate(def_id) = candidate {
@ -1476,14 +1480,16 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
(
BuiltinCandidate { has_nested: false }
| DiscriminantKindCandidate
| PointeeCandidate,
| PointeeCandidate
| ConstDropCandidate,
_,
) => true,
(
_,
BuiltinCandidate { has_nested: false }
| DiscriminantKindCandidate
| PointeeCandidate,
| PointeeCandidate
| ConstDropCandidate,
) => false,
(ParamCandidate(other), ParamCandidate(victim)) => {

3
compiler/rustc_ty_utils/src/instance.rs
View file

@ -386,7 +386,8 @@ fn resolve_associated_item<'tcx>(
| traits::ImplSource::TraitAlias(..)
| traits::ImplSource::DiscriminantKind(..)
| traits::ImplSource::Pointee(..)
| traits::ImplSource::TraitUpcasting(_) => None,
| traits::ImplSource::TraitUpcasting(_)
| traits::ImplSource::ConstDrop(_) => None,
})
}

51
src/test/ui/rfc-2632-const-trait-impl/const-drop.rs
View file

@ -23,6 +23,57 @@ const fn b() -> u8 {
const C: u8 = b();
macro_rules! implements_const_drop {
($($exp:expr),*$(,)?) => {
$(
const _: () = a($exp);
)*
}
}
#[allow(dead_code)]
mod t {
pub struct Foo;
pub enum Bar { A }
pub fn foo() {}
pub struct ConstDrop;
impl const Drop for ConstDrop {
fn drop(&mut self) {}
}
pub struct HasConstDrop(pub ConstDrop);
pub struct TrivialFields(pub u8, pub i8, pub usize, pub isize);
}
use t::*;
implements_const_drop! {
1u8,
2,
3.0,
Foo,
Bar::A,
foo,
ConstDrop,
HasConstDrop(ConstDrop),
TrivialFields(1, 2, 3, 4),
&1,
&1 as *const i32,
}
fn main() {
struct HasDropGlue(Box<u8>);
struct HasDropImpl;
impl Drop for HasDropImpl {
fn drop(&mut self) {
println!("not trivial drop");
}
}
// These types should pass because ~const in a non-const context should have no effect.
a(HasDropGlue(Box::new(0)));
a(HasDropImpl);
assert_eq!(C, 2);
}