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Auto merge of #129499 - fee1-dead-contrib:supereffects, r=compiler-errors

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properly elaborate effects implied bounds for super traits

Summary: This PR makes it so that we elaborate `<T as Tr>::Fx: EffectsCompat<somebool>` into `<T as SuperTr>::Fx: EffectsCompat<somebool>` when we know that `trait Tr: ~const SuperTr`.

Some discussion at https://github.com/rust-lang/project-const-traits/issues/2.

r? project-const-traits
`@rust-lang/project-const-traits:` how do we feel about this approach?
This commit is contained in:
bors 2024-09-30 00:30:09 +00:00
commit 4e91cedaed
11 changed files with 132 additions and 84 deletions
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44
compiler/rustc_hir_analysis/src/bounds.rs
View File

@ -91,12 +91,46 @@ impl<'tcx> Bounds<'tcx> {
}
tcx.consts.true_
}
(DefKind::Trait, ty::BoundConstness::ConstIfConst) => {
// we are in a trait, where `bound_trait_ref` could be:
// (1) a super trait `trait Foo: ~const Bar`.
// - This generates `<Self as Foo>::Effects: TyCompat<<Self as Bar>::Effects>`
//
// (2) a where clause `where for<..> Something: ~const Bar`.
// - This generates `for<..> <Self as Foo>::Effects: TyCompat<<Something as Bar>::Effects>`
let Some(own_fx) = tcx.associated_type_for_effects(defining_def_id) else {
tcx.dcx().span_delayed_bug(span, "should not have allowed `~const` on a trait that doesn't have `#[const_trait]`");
return;
};
let own_fx_ty = Ty::new_projection(
tcx,
own_fx,
ty::GenericArgs::identity_for_item(tcx, own_fx),
);
let Some(their_fx) = tcx.associated_type_for_effects(bound_trait_ref.def_id())
else {
tcx.dcx().span_delayed_bug(span, "`~const` on trait without Effects assoc");
return;
};
let their_fx_ty =
Ty::new_projection(tcx, their_fx, bound_trait_ref.skip_binder().args);
let compat = tcx.require_lang_item(LangItem::EffectsTyCompat, Some(span));
let clause = bound_trait_ref
.map_bound(|_| {
let trait_ref = ty::TraitRef::new(tcx, compat, [own_fx_ty, their_fx_ty]);
ty::ClauseKind::Trait(ty::TraitPredicate {
trait_ref,
polarity: ty::PredicatePolarity::Positive,
})
})
.upcast(tcx);
(
DefKind::Trait | DefKind::Impl { of_trait: true },
ty::BoundConstness::ConstIfConst,
) => {
// this is either a where clause on an impl/trait header or on a trait.
self.clauses.push((clause, span));
return;
}
(DefKind::Impl { of_trait: true }, ty::BoundConstness::ConstIfConst) => {
// this is a where clause on an impl header.
// push `<T as Tr>::Effects` into the set for the `Min` bound.
let Some(assoc) = tcx.associated_type_for_effects(bound_trait_ref.def_id()) else {
tcx.dcx().span_delayed_bug(span, "`~const` on trait without Effects assoc");

29
compiler/rustc_hir_analysis/src/collect/item_bounds.rs
View File

@ -360,33 +360,10 @@ pub(super) fn explicit_item_bounds_with_filter(
None => {}
}
if tcx.is_effects_desugared_assoc_ty(def_id.to_def_id()) {
let mut predicates = Vec::new();
let parent = tcx.local_parent(def_id);
let preds = tcx.explicit_predicates_of(parent);
if let ty::AssocItemContainer::TraitContainer = tcx.associated_item(def_id).container {
// for traits, emit `type Effects: TyCompat<<(T1::Effects, ..) as Min>::Output>`
let tup = Ty::new(tcx, ty::Tuple(preds.effects_min_tys));
// FIXME(effects) span
let span = tcx.def_span(def_id);
let assoc = tcx.require_lang_item(hir::LangItem::EffectsIntersectionOutput, Some(span));
let proj = Ty::new_projection(tcx, assoc, [tup]);
let self_proj = Ty::new_projection(
tcx,
def_id.to_def_id(),
ty::GenericArgs::identity_for_item(tcx, def_id),
);
let trait_ = tcx.require_lang_item(hir::LangItem::EffectsTyCompat, Some(span));
let trait_ref = ty::TraitRef::new(tcx, trait_, [self_proj, proj]);
predicates.push((ty::Binder::dummy(trait_ref).upcast(tcx), span));
}
return ty::EarlyBinder::bind(tcx.arena.alloc_from_iter(predicates));
}
let bounds = match tcx.hir_node_by_def_id(def_id) {
_ if tcx.is_effects_desugared_assoc_ty(def_id.to_def_id()) => {
associated_type_bounds(tcx, def_id, &[], tcx.def_span(def_id), filter)
}
hir::Node::TraitItem(hir::TraitItem {
kind: hir::TraitItemKind::Type(bounds, _),
span,

2
compiler/rustc_middle/src/ty/context.rs
View File

@ -622,11 +622,13 @@ bidirectional_lang_item_map! {
Destruct,
DiscriminantKind,
DynMetadata,
EffectsCompat,
EffectsIntersection,
EffectsIntersectionOutput,
EffectsMaybe,
EffectsNoRuntime,
EffectsRuntime,
EffectsTyCompat,
Fn,
FnMut,
FnOnce,

65
compiler/rustc_type_ir/src/elaborate.rs
View File

@ -4,6 +4,7 @@ use smallvec::smallvec;
use crate::data_structures::HashSet;
use crate::inherent::*;
use crate::lang_items::TraitSolverLangItem;
use crate::outlives::{Component, push_outlives_components};
use crate::{self as ty, Interner, Upcast as _};
@ -89,6 +90,70 @@ impl<I: Interner, O: Elaboratable<I>> Elaborator<I, O> {
return;
}
// HACK(effects): The following code is required to get implied bounds for effects associated
// types to work with super traits.
//
// Suppose `data` is a trait predicate with the form `<T as Tr>::Fx: EffectsCompat<somebool>`
// and we know that `trait Tr: ~const SuperTr`, we need to elaborate this predicate into
// `<T as SuperTr>::Fx: EffectsCompat<somebool>`.
//
// Since the semantics for elaborating bounds about effects is equivalent to elaborating
// bounds about super traits (elaborate `T: Tr` into `T: SuperTr`), we place effects elaboration
// next to super trait elaboration.
if cx.is_lang_item(data.def_id(), TraitSolverLangItem::EffectsCompat)
&& matches!(self.mode, Filter::All)
{
// first, ensure that the predicate we've got looks like a `<T as Tr>::Fx: EffectsCompat<somebool>`.
if let ty::Alias(ty::AliasTyKind::Projection, alias_ty) = data.self_ty().kind()
{
// look for effects-level bounds that look like `<Self as Tr>::Fx: TyCompat<<Self as SuperTr>::Fx>`
// on the trait, which is proof to us that `Tr: ~const SuperTr`. We're looking for bounds on the
// associated trait, so we use `explicit_implied_predicates_of` since it gives us more than just
// `Self: SuperTr` bounds.
let bounds = cx.explicit_implied_predicates_of(cx.parent(alias_ty.def_id));
// instantiate the implied bounds, so we get `<T as Tr>::Fx` and not `<Self as Tr>::Fx`.
let elaborated = bounds.iter_instantiated(cx, alias_ty.args).filter_map(
|(clause, _)| {
let ty::ClauseKind::Trait(tycompat_bound) =
clause.kind().skip_binder()
else {
return None;
};
if !cx.is_lang_item(
tycompat_bound.def_id(),
TraitSolverLangItem::EffectsTyCompat,
) {
return None;
}
// extract `<T as SuperTr>::Fx` from the `TyCompat` bound.
let supertrait_effects_ty =
tycompat_bound.trait_ref.args.type_at(1);
let ty::Alias(ty::AliasTyKind::Projection, supertrait_alias_ty) =
supertrait_effects_ty.kind()
else {
return None;
};
// The self types (`T`) must be equal for `<T as Tr>::Fx` and `<T as SuperTr>::Fx`.
if supertrait_alias_ty.self_ty() != alias_ty.self_ty() {
return None;
};
// replace the self type in the original bound `<T as Tr>::Fx: EffectsCompat<somebool>`
// to the effects type of the super trait. (`<T as SuperTr>::Fx`)
let elaborated_bound = data.with_self_ty(cx, supertrait_effects_ty);
Some(
elaboratable
.child(bound_clause.rebind(elaborated_bound).upcast(cx)),
)
},
);
self.extend_deduped(elaborated);
}
}
let map_to_child_clause =
|(index, (clause, span)): (usize, (I::Clause, I::Span))| {
elaboratable.child_with_derived_cause(

2
compiler/rustc_type_ir/src/lang_items.rs
View File

@ -20,11 +20,13 @@ pub enum TraitSolverLangItem {
Destruct,
DiscriminantKind,
DynMetadata,
EffectsCompat,
EffectsIntersection,
EffectsIntersectionOutput,
EffectsMaybe,
EffectsNoRuntime,
EffectsRuntime,
EffectsTyCompat,
Fn,
FnMut,
FnOnce,

2
tests/ui/rfcs/rfc-2632-const-trait-impl/super-traits-fail-3.rs
View File

@ -3,7 +3,7 @@
#![feature(const_trait_impl, effects)]
//@ revisions: yy yn ny nn
//@[yy] known-bug: #110395
//@[yy] check-pass
#[cfg_attr(any(yy, yn), const_trait)]
trait Foo {

22
tests/ui/rfcs/rfc-2632-const-trait-impl/super-traits-fail-3.yy.stderr
View File

@ -1,22 +0,0 @@
error[E0277]: the trait bound `Foo::{synthetic#0}: ~const Compat` is not satisfied
--> $DIR/super-traits-fail-3.rs:22:7
|
LL | x.a();
| ^ the trait `~const Compat` is not implemented for `Foo::{synthetic#0}`
|
note: required by a bound in `Foo::a`
--> $DIR/super-traits-fail-3.rs:8:25
|
LL | #[cfg_attr(any(yy, yn), const_trait)]
| ^^^^^^^^^^^ required by this bound in `Foo::a`
LL | trait Foo {
LL | fn a(&self);
| - required by a bound in this associated function
help: consider further restricting the associated type
|
LL | const fn foo<T: ~const Bar>(x: &T) where Foo::{synthetic#0}: ~const Compat {
| +++++++++++++++++++++++++++++++++++++++
error: aborting due to 1 previous error
For more information about this error, try `rustc --explain E0277`.

2
tests/ui/rfcs/rfc-2632-const-trait-impl/super-traits-fail.rs
View File

@ -17,6 +17,6 @@ impl Foo for S {
}
impl const Bar for S {}
// FIXME(effects) bad span
//~^ ERROR the trait bound
fn main() {}

23
tests/ui/rfcs/rfc-2632-const-trait-impl/super-traits-fail.stderr
View File

@ -1,11 +1,24 @@
error[E0277]: the trait bound `Maybe: TyCompat<<(Foo::{synthetic#0},) as std::marker::effects::Intersection>::Output>` is not satisfied
error[E0277]: the trait bound `Bar::{synthetic#0}: TyCompat<Foo::{synthetic#0}>` is not satisfied
--> $DIR/super-traits-fail.rs:19:12
|
LL | impl const Bar for S {}
| ^^^ the trait `TyCompat<Foo::{synthetic#0}>` is not implemented for `Bar::{synthetic#0}`, which is required by `S: Bar`
|
= help: the trait `Bar` is implemented for `S`
note: required for `S` to implement `Bar`
--> $DIR/super-traits-fail.rs:12:7
|
LL | trait Bar: ~const Foo {}
| ^^^
error[E0277]: the trait bound `Maybe: TyCompat<Foo::{synthetic#0}>` is not satisfied
|
note: required by a bound in `Bar::{synthetic#0}`
--> $DIR/super-traits-fail.rs:11:1
--> $DIR/super-traits-fail.rs:12:12
|
LL | #[const_trait]
| ^^^^^^^^^^^^^^ required by this bound in `Bar::{synthetic#0}`
LL | trait Bar: ~const Foo {}
| ^^^^^^^^^^ required by this bound in `Bar::{synthetic#0}`
error: aborting due to 1 previous error
error: aborting due to 2 previous errors
For more information about this error, try `rustc --explain E0277`.

3
tests/ui/rfcs/rfc-2632-const-trait-impl/super-traits.rs
View File

@ -1,5 +1,4 @@
// FIXME(effects) check-pass
//@ known-bug: #110395
//@ check-pass
//@ compile-flags: -Znext-solver
#![allow(incomplete_features)]
#![feature(const_trait_impl, effects)]

22
tests/ui/rfcs/rfc-2632-const-trait-impl/super-traits.stderr
View File

@ -1,22 +0,0 @@
error[E0277]: the trait bound `Foo::{synthetic#0}: ~const Compat` is not satisfied
--> $DIR/super-traits.rs:23:7
|
LL | t.a();
| ^ the trait `~const Compat` is not implemented for `Foo::{synthetic#0}`
|
note: required by a bound in `Foo::a`
--> $DIR/super-traits.rs:7:1
|
LL | #[const_trait]
| ^^^^^^^^^^^^^^ required by this bound in `Foo::a`
LL | trait Foo {
LL | fn a(&self);
| - required by a bound in this associated function
help: consider further restricting the associated type
|
LL | const fn foo<T: ~const Bar>(t: &T) where Foo::{synthetic#0}: ~const Compat {
| +++++++++++++++++++++++++++++++++++++++
error: aborting due to 1 previous error
For more information about this error, try `rustc --explain E0277`.