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Rollup merge of #116800 - compiler-errors:rpitit-gat-outlives, r=jackh726

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Fix implied outlives check for GAT in RPITIT

We enforce certain `Self: 'lt` bounds for GATs to save space for more sophisticated implied bounds, but those currently operate on the HIR. Code was easily reworked to operate on def-ids so that we can properly let these suggestions propagate through synthetic associated types like RPITITs and AFITs.

r? `@jackh726` or `@aliemjay`

Fixes #116789
This commit is contained in:
Guillaume Gomez 2023-10-16 23:58:04 +02:00 committed by GitHub
commit d0ade3f1ba
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3 changed files with 68 additions and 33 deletions
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60
compiler/rustc_hir_analysis/src/check/wfcheck.rs
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@ -314,9 +314,10 @@ fn check_trait_item(tcx: TyCtxt<'_>, trait_item: &hir::TraitItem<'_>) {
/// fn into_iter<'a>(&'a self) -> Self::Iter<'a>;
/// }
/// ```
fn check_gat_where_clauses(tcx: TyCtxt<'_>, associated_items: &[hir::TraitItemRef]) {
fn check_gat_where_clauses(tcx: TyCtxt<'_>, trait_def_id: LocalDefId) {
// Associates every GAT's def_id to a list of possibly missing bounds detected by this lint.
let mut required_bounds_by_item = FxHashMap::default();
let associated_items = tcx.associated_items(trait_def_id);
// Loop over all GATs together, because if this lint suggests adding a where-clause bound
// to one GAT, it might then require us to an additional bound on another GAT.
@ -325,8 +326,8 @@ fn check_gat_where_clauses(tcx: TyCtxt<'_>, associated_items: &[hir::TraitItemRe
// those GATs.
loop {
let mut should_continue = false;
for gat_item in associated_items {
let gat_def_id = gat_item.id.owner_id;
for gat_item in associated_items.in_definition_order() {
let gat_def_id = gat_item.def_id.expect_local();
let gat_item = tcx.associated_item(gat_def_id);
// If this item is not an assoc ty, or has no args, then it's not a GAT
if gat_item.kind != ty::AssocKind::Type {
@ -342,8 +343,8 @@ fn check_gat_where_clauses(tcx: TyCtxt<'_>, associated_items: &[hir::TraitItemRe
// This is calculated by taking the intersection of the bounds that each item
// constrains the GAT with individually.
let mut new_required_bounds: Option<FxHashSet<ty::Clause<'_>>> = None;
for item in associated_items {
let item_def_id = item.id.owner_id;
for item in associated_items.in_definition_order() {
let item_def_id = item.def_id.expect_local();
// Skip our own GAT, since it does not constrain itself at all.
if item_def_id == gat_def_id {
continue;
@ -351,9 +352,9 @@ fn check_gat_where_clauses(tcx: TyCtxt<'_>, associated_items: &[hir::TraitItemRe
let param_env = tcx.param_env(item_def_id);
let item_required_bounds = match item.kind {
let item_required_bounds = match tcx.associated_item(item_def_id).kind {
// In our example, this corresponds to `into_iter` method
hir::AssocItemKind::Fn { .. } => {
ty::AssocKind::Fn => {
// For methods, we check the function signature's return type for any GATs
// to constrain. In the `into_iter` case, we see that the return type
// `Self::Iter<'a>` is a GAT we want to gather any potential missing bounds from.
@ -369,12 +370,12 @@ fn check_gat_where_clauses(tcx: TyCtxt<'_>, associated_items: &[hir::TraitItemRe
// We also assume that all of the function signature's parameter types
// are well formed.
&sig.inputs().iter().copied().collect(),
gat_def_id.def_id,
gat_def_id,
gat_generics,
)
}
// In our example, this corresponds to the `Iter` and `Item` associated types
hir::AssocItemKind::Type => {
ty::AssocKind::Type => {
// If our associated item is a GAT with missing bounds, add them to
// the param-env here. This allows this GAT to propagate missing bounds
// to other GATs.
@ -391,11 +392,11 @@ fn check_gat_where_clauses(tcx: TyCtxt<'_>, associated_items: &[hir::TraitItemRe
.instantiate_identity_iter_copied()
.collect::<Vec<_>>(),
&FxIndexSet::default(),
gat_def_id.def_id,
gat_def_id,
gat_generics,
)
}
hir::AssocItemKind::Const => None,
ty::AssocKind::Const => None,
};
if let Some(item_required_bounds) = item_required_bounds {
@ -431,7 +432,12 @@ fn check_gat_where_clauses(tcx: TyCtxt<'_>, associated_items: &[hir::TraitItemRe
}
for (gat_def_id, required_bounds) in required_bounds_by_item {
let gat_item_hir = tcx.hir().expect_trait_item(gat_def_id.def_id);
// Don't suggest adding `Self: 'a` to a GAT that can't be named
if tcx.is_impl_trait_in_trait(gat_def_id.to_def_id()) {
continue;
}
let gat_item_hir = tcx.hir().expect_trait_item(gat_def_id);
debug!(?required_bounds);
let param_env = tcx.param_env(gat_def_id);
@ -441,21 +447,16 @@ fn check_gat_where_clauses(tcx: TyCtxt<'_>, associated_items: &[hir::TraitItemRe
ty::ClauseKind::RegionOutlives(ty::OutlivesPredicate(a, b)) => {
!region_known_to_outlive(
tcx,
gat_def_id.def_id,
gat_def_id,
param_env,
&FxIndexSet::default(),
a,
b,
)
}
ty::ClauseKind::TypeOutlives(ty::OutlivesPredicate(a, b)) => !ty_known_to_outlive(
tcx,
gat_def_id.def_id,
param_env,
&FxIndexSet::default(),
a,
b,
),
ty::ClauseKind::TypeOutlives(ty::OutlivesPredicate(a, b)) => {
!ty_known_to_outlive(tcx, gat_def_id, param_env, &FxIndexSet::default(), a, b)
}
_ => bug!("Unexpected ClauseKind"),
})
.map(|clause| clause.to_string())
@ -534,7 +535,7 @@ fn augment_param_env<'tcx>(
fn gather_gat_bounds<'tcx, T: TypeFoldable<TyCtxt<'tcx>>>(
tcx: TyCtxt<'tcx>,
param_env: ty::ParamEnv<'tcx>,
item_def_id: hir::OwnerId,
item_def_id: LocalDefId,
to_check: T,
wf_tys: &FxIndexSet<Ty<'tcx>>,
gat_def_id: LocalDefId,
@ -567,7 +568,7 @@ fn gather_gat_bounds<'tcx, T: TypeFoldable<TyCtxt<'tcx>>>(
// reflected in a where clause on the GAT itself.
for (ty, ty_idx) in &types {
// In our example, requires that `Self: 'a`
if ty_known_to_outlive(tcx, item_def_id.def_id, param_env, &wf_tys, *ty, *region_a) {
if ty_known_to_outlive(tcx, item_def_id, param_env, &wf_tys, *ty, *region_a) {
debug!(?ty_idx, ?region_a_idx);
debug!("required clause: {ty} must outlive {region_a}");
// Translate into the generic parameters of the GAT. In
@ -606,14 +607,7 @@ fn gather_gat_bounds<'tcx, T: TypeFoldable<TyCtxt<'tcx>>>(
if matches!(**region_b, ty::ReStatic | ty::ReError(_)) || region_a == region_b {
continue;
}
if region_known_to_outlive(
tcx,
item_def_id.def_id,
param_env,
&wf_tys,
*region_a,
*region_b,
) {
if region_known_to_outlive(tcx, item_def_id, param_env, &wf_tys, *region_a, *region_b) {
debug!(?region_a_idx, ?region_b_idx);
debug!("required clause: {region_a} must outlive {region_b}");
// Translate into the generic parameters of the GAT.
@ -1114,8 +1108,8 @@ fn check_trait(tcx: TyCtxt<'_>, item: &hir::Item<'_>) {
});
// Only check traits, don't check trait aliases
if let hir::ItemKind::Trait(_, _, _, _, items) = item.kind {
check_gat_where_clauses(tcx, items);
if let hir::ItemKind::Trait(..) = item.kind {
check_gat_where_clauses(tcx, item.owner_id.def_id);
}
}

17
tests/ui/impl-trait/in-trait/gat-outlives.rs Normal file
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@ -0,0 +1,17 @@
// edition: 2021
use std::future::Future;
trait Trait {
type Gat<'a>;
//~^ ERROR missing required bound on `Gat`
async fn foo(&self) -> Self::Gat<'_>;
}
trait Trait2 {
type Gat<'a>;
//~^ ERROR missing required bound on `Gat`
async fn foo(&self) -> impl Future<Output = Self::Gat<'_>>;
}
fn main() {}

24
tests/ui/impl-trait/in-trait/gat-outlives.stderr Normal file
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@ -0,0 +1,24 @@
error: missing required bound on `Gat`
--> $DIR/gat-outlives.rs:6:5
|
LL | type Gat<'a>;
| ^^^^^^^^^^^^-
| |
| help: add the required where clause: `where Self: 'a`
|
= note: this bound is currently required to ensure that impls have maximum flexibility
= note: we are soliciting feedback, see issue #87479 <https://github.com/rust-lang/rust/issues/87479> for more information
error: missing required bound on `Gat`
--> $DIR/gat-outlives.rs:12:5
|
LL | type Gat<'a>;
| ^^^^^^^^^^^^-
| |
| help: add the required where clause: `where Self: 'a`
|
= note: this bound is currently required to ensure that impls have maximum flexibility
= note: we are soliciting feedback, see issue #87479 <https://github.com/rust-lang/rust/issues/87479> for more information
error: aborting due to 2 previous errors