bjoernager/rust
bjoernager/rust
1
Fork 0
Code Activity

Auto merge of #121123 - compiler-errors:item-assumptions, r=oli-obk

Browse source 
Split an item bounds and an item's super predicates

This is the moral equivalent of #107614, but instead for predicates this applies to **item bounds**. This PR splits out the item bounds (i.e. *all* predicates that are assumed to hold for the alias) from the item *super predicates*, which are the subset of item bounds which share the same self type as the alias.

## Why?

Much like #107614, there are places in the compiler where we *only* care about super-predicates, and considering predicates that possibly don't have anything to do with the alias is problematic. This includes things like closure signature inference (which is at its core searching for `Self: Fn(..)` style bounds), but also lints like `#[must_use]`, error reporting for aliases, computing type outlives predicates.

Even in cases where considering all of the `item_bounds` doesn't lead to bugs, unnecessarily considering irrelevant bounds does lead to a regression (#121121) due to doing extra work in the solver.

## Example 1 - Trait Aliases

This is best explored via an example:

```
type TAIT<T> = impl TraitAlias<T>;

trait TraitAlias<T> = A + B where T: C;
```

The item bounds list for `Tait<T>` will include:
* `Tait<T>: A`
* `Tait<T>: B`
* `T: C`

While `item_super_predicates` query will include just the first two predicates.

Side-note: You may wonder why `T: C` is included in the item bounds for `TAIT`? This is because when we elaborate `TraitAlias<T>`, we will also elaborate all the predicates on the trait.

## Example 2 - Associated Type Bounds

```
type TAIT<T> = impl Iterator<Item: A>;
```

The `item_bounds` list for `TAIT<T>` will include:
* `Tait<T>: Iterator`
* `<Tait<T> as Iterator>::Item: A`

But the `item_super_predicates` will just include the first bound, since that's the only bound that is relevant to the *alias* itself.

## So what

This leads to some diagnostics duplication just like #107614, but none of it will be user-facing. We only see it in the UI test suite because we explicitly disable diagnostic deduplication.

Regarding naming, I went with `super_predicates` kind of arbitrarily; this can easily be changed, but I'd consider better names as long as we don't block this PR in perpetuity.
This commit is contained in:
bors 2024-03-21 06:12:24 +00:00
commit 47dd709bed
74 changed files with 757 additions and 174 deletions
Download patch file Download diff file Expand all files Collapse all files

2
compiler/rustc_hir_analysis/src/check/mod.rs
View file

@ -431,7 +431,7 @@ fn fn_sig_suggestion<'tcx>(
let asyncness = if tcx.asyncness(assoc.def_id).is_async() {
output = if let ty::Alias(_, alias_ty) = *output.kind() {
tcx.explicit_item_bounds(alias_ty.def_id)
tcx.explicit_item_super_predicates(alias_ty.def_id)
.iter_instantiated_copied(tcx, alias_ty.args)
.find_map(|(bound, _)| bound.as_projection_clause()?.no_bound_vars()?.term.ty())
.unwrap_or_else(|| {

7
compiler/rustc_hir_analysis/src/collect.rs
View file

@ -61,6 +61,9 @@ pub fn provide(providers: &mut Providers) {
type_alias_is_lazy: type_of::type_alias_is_lazy,
item_bounds: item_bounds::item_bounds,
explicit_item_bounds: item_bounds::explicit_item_bounds,
item_super_predicates: item_bounds::item_super_predicates,
explicit_item_super_predicates: item_bounds::explicit_item_super_predicates,
item_non_self_assumptions: item_bounds::item_non_self_assumptions,
generics_of: generics_of::generics_of,
predicates_of: predicates_of::predicates_of,
predicates_defined_on,
@ -633,7 +636,9 @@ fn convert_item(tcx: TyCtxt<'_>, item_id: hir::ItemId) {
tcx.ensure().generics_of(def_id);
tcx.ensure().predicates_of(def_id);
tcx.ensure().explicit_item_bounds(def_id);
tcx.ensure().explicit_item_super_predicates(def_id);
tcx.ensure().item_bounds(def_id);
tcx.ensure().item_super_predicates(def_id);
}
hir::ItemKind::TyAlias(..) => {
@ -689,6 +694,7 @@ fn convert_trait_item(tcx: TyCtxt<'_>, trait_item_id: hir::TraitItemId) {
hir::TraitItemKind::Type(_, Some(_)) => {
tcx.ensure().item_bounds(def_id);
tcx.ensure().item_super_predicates(def_id);
tcx.ensure().type_of(def_id);
// Account for `type T = _;`.
let mut visitor = HirPlaceholderCollector::default();
@ -698,6 +704,7 @@ fn convert_trait_item(tcx: TyCtxt<'_>, trait_item_id: hir::TraitItemId) {
hir::TraitItemKind::Type(_, None) => {
tcx.ensure().item_bounds(def_id);
tcx.ensure().item_super_predicates(def_id);
// #74612: Visit and try to find bad placeholders
// even if there is no concrete type.
let mut visitor = HirPlaceholderCollector::default();

54
compiler/rustc_hir_analysis/src/collect/item_bounds.rs
View file

@ -1,5 +1,6 @@
use super::ItemCtxt;
use crate::astconv::{AstConv, PredicateFilter};
use rustc_data_structures::fx::FxIndexSet;
use rustc_hir as hir;
use rustc_infer::traits::util;
use rustc_middle::ty::GenericArgs;
@ -19,6 +20,7 @@ fn associated_type_bounds<'tcx>(
assoc_item_def_id: LocalDefId,
ast_bounds: &'tcx [hir::GenericBound<'tcx>],
span: Span,
filter: PredicateFilter,
) -> &'tcx [(ty::Clause<'tcx>, Span)] {
let item_ty = Ty::new_projection(
tcx,
@ -27,7 +29,7 @@ fn associated_type_bounds<'tcx>(
);
let icx = ItemCtxt::new(tcx, assoc_item_def_id);
let mut bounds = icx.astconv().compute_bounds(item_ty, ast_bounds, PredicateFilter::All);
let mut bounds = icx.astconv().compute_bounds(item_ty, ast_bounds, filter);
// Associated types are implicitly sized unless a `?Sized` bound is found
icx.astconv().add_implicitly_sized(&mut bounds, item_ty, ast_bounds, None, span);
@ -63,10 +65,11 @@ fn opaque_type_bounds<'tcx>(
ast_bounds: &'tcx [hir::GenericBound<'tcx>],
item_ty: Ty<'tcx>,
span: Span,
filter: PredicateFilter,
) -> &'tcx [(ty::Clause<'tcx>, Span)] {
ty::print::with_reduced_queries!({
let icx = ItemCtxt::new(tcx, opaque_def_id);
let mut bounds = icx.astconv().compute_bounds(item_ty, ast_bounds, PredicateFilter::All);
let mut bounds = icx.astconv().compute_bounds(item_ty, ast_bounds, filter);
// Opaque types are implicitly sized unless a `?Sized` bound is found
icx.astconv().add_implicitly_sized(&mut bounds, item_ty, ast_bounds, None, span);
debug!(?bounds);
@ -78,6 +81,21 @@ fn opaque_type_bounds<'tcx>(
pub(super) fn explicit_item_bounds(
tcx: TyCtxt<'_>,
def_id: LocalDefId,
) -> ty::EarlyBinder<&'_ [(ty::Clause<'_>, Span)]> {
explicit_item_bounds_with_filter(tcx, def_id, PredicateFilter::All)
}
pub(super) fn explicit_item_super_predicates(
tcx: TyCtxt<'_>,
def_id: LocalDefId,
) -> ty::EarlyBinder<&'_ [(ty::Clause<'_>, Span)]> {
explicit_item_bounds_with_filter(tcx, def_id, PredicateFilter::SelfOnly)
}
pub(super) fn explicit_item_bounds_with_filter(
tcx: TyCtxt<'_>,
def_id: LocalDefId,
filter: PredicateFilter,
) -> ty::EarlyBinder<&'_ [(ty::Clause<'_>, Span)]> {
match tcx.opt_rpitit_info(def_id.to_def_id()) {
// RPITIT's bounds are the same as opaque type bounds, but with
@ -95,6 +113,7 @@ pub(super) fn explicit_item_bounds(
ty::GenericArgs::identity_for_item(tcx, def_id),
),
item.span,
filter,
));
}
Some(ty::ImplTraitInTraitData::Impl { .. }) => span_bug!(
@ -109,7 +128,7 @@ pub(super) fn explicit_item_bounds(
kind: hir::TraitItemKind::Type(bounds, _),
span,
..
}) => associated_type_bounds(tcx, def_id, bounds, *span),
}) => associated_type_bounds(tcx, def_id, bounds, *span, filter),
hir::Node::Item(hir::Item {
kind: hir::ItemKind::OpaqueTy(hir::OpaqueTy { bounds, in_trait: false, .. }),
span,
@ -117,7 +136,7 @@ pub(super) fn explicit_item_bounds(
}) => {
let args = GenericArgs::identity_for_item(tcx, def_id);
let item_ty = Ty::new_opaque(tcx, def_id.to_def_id(), args);
opaque_type_bounds(tcx, def_id, bounds, item_ty, *span)
opaque_type_bounds(tcx, def_id, bounds, item_ty, *span, filter)
}
// Since RPITITs are astconv'd as projections in `ast_ty_to_ty`, when we're asking
// for the item bounds of the *opaques* in a trait's default method signature, we
@ -135,7 +154,7 @@ pub(super) fn explicit_item_bounds(
let args = GenericArgs::identity_for_item(tcx, def_id);
let item_ty = Ty::new_opaque(tcx, def_id.to_def_id(), args);
tcx.arena.alloc_slice(
&opaque_type_bounds(tcx, def_id, bounds, item_ty, *span)
&opaque_type_bounds(tcx, def_id, bounds, item_ty, *span, filter)
.to_vec()
.fold_with(&mut AssocTyToOpaque { tcx, fn_def_id: fn_def_id.to_def_id() }),
)
@ -155,6 +174,31 @@ pub(super) fn item_bounds(
})
}
pub(super) fn item_super_predicates(
tcx: TyCtxt<'_>,
def_id: DefId,
) -> ty::EarlyBinder<&'_ ty::List<ty::Clause<'_>>> {
tcx.explicit_item_super_predicates(def_id).map_bound(|bounds| {
tcx.mk_clauses_from_iter(
util::elaborate(tcx, bounds.iter().map(|&(bound, _span)| bound)).filter_only_self(),
)
})
}
pub(super) fn item_non_self_assumptions(
tcx: TyCtxt<'_>,
def_id: DefId,
) -> ty::EarlyBinder<&'_ ty::List<ty::Clause<'_>>> {
let all_bounds: FxIndexSet<_> = tcx.item_bounds(def_id).skip_binder().iter().collect();
let own_bounds: FxIndexSet<_> =
tcx.item_super_predicates(def_id).skip_binder().iter().collect();
if all_bounds.len() == own_bounds.len() {
ty::EarlyBinder::bind(ty::List::empty())
} else {
ty::EarlyBinder::bind(tcx.mk_clauses_from_iter(all_bounds.difference(&own_bounds).copied()))
}
}
struct AssocTyToOpaque<'tcx> {
tcx: TyCtxt<'tcx>,
fn_def_id: DefId,