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Compute variances for lazy type aliases
1 parent 8131b97 commit 263a0de

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7 files changed

+109
-13
lines changed

7 files changed

+109
-13
lines changed

‎compiler/rustc_hir_analysis/src/check/wfcheck.rs

+22-4
Original file line numberDiff line numberDiff line change
@@ -245,13 +245,14 @@ fn check_item<'tcx>(tcx: TyCtxt<'tcx>, item: &'tcx hir::Item<'tcx>) {
245245
}
246246
// `ForeignItem`s are handled separately.
247247
hir::ItemKind::ForeignMod { .. } => {}
248-
hir::ItemKind::TyAlias(hir_ty, ..) => {
248+
hir::ItemKind::TyAlias(hir_ty, ast_generics) => {
249249
if tcx.features().lazy_type_alias
250250
|| tcx.type_of(item.owner_id).skip_binder().has_opaque_types()
251251
{
252252
// Bounds of lazy type aliases and of eager ones that contain opaque types are respected.
253253
// E.g: `type X = impl Trait;`, `type X = (impl Trait, Y);`.
254254
check_item_type(tcx, def_id, hir_ty.span, UnsizedHandling::Allow);
255+
check_variances_for_type_defn(tcx, item, ast_generics);
255256
}
256257
}
257258
_ => {}
@@ -1700,10 +1701,27 @@ fn check_variances_for_type_defn<'tcx>(
17001701
hir_generics: &hir::Generics<'_>,
17011702
) {
17021703
let identity_args = ty::GenericArgs::identity_for_item(tcx, item.owner_id);
1703-
for field in tcx.adt_def(item.owner_id).all_fields() {
1704-
if field.ty(tcx, identity_args).references_error() {
1705-
return;
1704+
1705+
match item.kind {
1706+
ItemKind::Enum(..) | ItemKind::Struct(..) | ItemKind::Union(..) => {
1707+
for field in tcx.adt_def(item.owner_id).all_fields() {
1708+
if field.ty(tcx, identity_args).references_error() {
1709+
return;
1710+
}
1711+
}
1712+
}
1713+
ItemKind::TyAlias(..) => {
1714+
let ty = tcx.type_of(item.owner_id).instantiate_identity();
1715+
1716+
if tcx.features().lazy_type_alias || ty.has_opaque_types() {
1717+
if ty.references_error() {
1718+
return;
1719+
}
1720+
} else {
1721+
bug!();
1722+
}
17061723
}
1724+
_ => bug!(),
17071725
}
17081726

17091727
let ty_predicates = tcx.predicates_of(item.owner_id);

‎compiler/rustc_hir_analysis/src/variance/constraints.rs

+25-3
Original file line numberDiff line numberDiff line change
@@ -6,7 +6,7 @@
66
use hir::def_id::{DefId, LocalDefId};
77
use rustc_hir as hir;
88
use rustc_hir::def::DefKind;
9-
use rustc_middle::ty::{self, Ty, TyCtxt};
9+
use rustc_middle::ty::{self, Ty, TyCtxt, TypeVisitableExt};
1010
use rustc_middle::ty::{GenericArgKind, GenericArgsRef};
1111

1212
use super::terms::VarianceTerm::*;
@@ -78,6 +78,12 @@ pub fn add_constraints_from_crate<'a, 'tcx>(
7878
}
7979
}
8080
DefKind::Fn | DefKind::AssocFn => constraint_cx.build_constraints_for_item(def_id),
81+
DefKind::TyAlias
82+
if tcx.features().lazy_type_alias
83+
|| tcx.type_of(def_id).instantiate_identity().has_opaque_types() =>
84+
{
85+
constraint_cx.build_constraints_for_item(def_id)
86+
}
8187
_ => {}
8288
}
8389
}
@@ -101,7 +107,18 @@ impl<'a, 'tcx> ConstraintContext<'a, 'tcx> {
101107

102108
let inferred_start = self.terms_cx.inferred_starts[&def_id];
103109
let current_item = &CurrentItem { inferred_start };
104-
match tcx.type_of(def_id).instantiate_identity().kind() {
110+
let ty = tcx.type_of(def_id).instantiate_identity();
111+
112+
// The type as returned by `type_of` is the underlying type and generally not a weak projection.
113+
// Therefore we need to check the `DefKind` first.
114+
if let DefKind::TyAlias = tcx.def_kind(def_id)
115+
&& (tcx.features().lazy_type_alias || ty.has_opaque_types())
116+
{
117+
self.add_constraints_from_ty(current_item, ty, self.covariant);
118+
return;
119+
}
120+
121+
match ty.kind() {
105122
ty::Adt(def, _) => {
106123
// Not entirely obvious: constraints on structs/enums do not
107124
// affect the variance of their type parameters. See discussion
@@ -127,6 +144,7 @@ impl<'a, 'tcx> ConstraintContext<'a, 'tcx> {
127144
}
128145

129146
ty::Error(_) => {}
147+
130148
_ => {
131149
span_bug!(
132150
tcx.def_span(def_id),
@@ -252,10 +270,14 @@ impl<'a, 'tcx> ConstraintContext<'a, 'tcx> {
252270
self.add_constraints_from_args(current, def.did(), args, variance);
253271
}
254272

255-
ty::Alias(_, ref data) => {
273+
ty::Alias(ty::Projection | ty::Inherent | ty::Opaque, ref data) => {
256274
self.add_constraints_from_invariant_args(current, data.args, variance);
257275
}
258276

277+
ty::Alias(ty::Weak, ref data) => {
278+
self.add_constraints_from_args(current, data.def_id, data.args, variance);
279+
}
280+
259281
ty::Dynamic(data, r, _) => {
260282
// The type `dyn Trait<T> +'a` is covariant w/r/t `'a`:
261283
self.add_constraints_from_region(current, r, variance);

‎compiler/rustc_hir_analysis/src/variance/mod.rs

+9-1
Original file line numberDiff line numberDiff line change
@@ -8,7 +8,7 @@ use rustc_hir::def::DefKind;
88
use rustc_hir::def_id::{DefId, LocalDefId};
99
use rustc_middle::query::Providers;
1010
use rustc_middle::ty::{self, CrateVariancesMap, GenericArgsRef, Ty, TyCtxt};
11-
use rustc_middle::ty::{TypeSuperVisitable, TypeVisitable};
11+
use rustc_middle::ty::{TypeSuperVisitable, TypeVisitable, TypeVisitableExt};
1212
use std::ops::ControlFlow;
1313

1414
/// Defines the `TermsContext` basically houses an arena where we can
@@ -56,6 +56,14 @@ fn variances_of(tcx: TyCtxt<'_>, item_def_id: LocalDefId) -> &[ty::Variance] {
5656
let crate_map = tcx.crate_variances(());
5757
return crate_map.variances.get(&item_def_id.to_def_id()).copied().unwrap_or(&[]);
5858
}
59+
DefKind::TyAlias
60+
if tcx.features().lazy_type_alias
61+
|| tcx.type_of(item_def_id).instantiate_identity().has_opaque_types() =>
62+
{
63+
// These are inferred.
64+
let crate_map = tcx.crate_variances(());
65+
return crate_map.variances.get(&item_def_id.to_def_id()).copied().unwrap_or(&[]);
66+
}
5967
DefKind::OpaqueTy => {
6068
return variance_of_opaque(tcx, item_def_id);
6169
}

‎compiler/rustc_hir_analysis/src/variance/terms.rs

+7-1
Original file line numberDiff line numberDiff line change
@@ -12,7 +12,7 @@
1212
use rustc_arena::DroplessArena;
1313
use rustc_hir::def::DefKind;
1414
use rustc_hir::def_id::{LocalDefId, LocalDefIdMap};
15-
use rustc_middle::ty::{self, TyCtxt};
15+
use rustc_middle::ty::{self, TyCtxt, TypeVisitableExt};
1616
use std::fmt;
1717

1818
use self::VarianceTerm::*;
@@ -97,6 +97,12 @@ pub fn determine_parameters_to_be_inferred<'a, 'tcx>(
9797
}
9898
}
9999
DefKind::Fn | DefKind::AssocFn => terms_cx.add_inferreds_for_item(def_id),
100+
DefKind::TyAlias
101+
if tcx.features().lazy_type_alias
102+
|| tcx.type_of(def_id).instantiate_identity().has_opaque_types() =>
103+
{
104+
terms_cx.add_inferreds_for_item(def_id)
105+
}
100106
_ => {}
101107
}
102108
}

‎compiler/rustc_metadata/src/rmeta/encoder.rs

+7-3
Original file line numberDiff line numberDiff line change
@@ -30,6 +30,7 @@ use rustc_middle::query::Providers;
3030
use rustc_middle::traits::specialization_graph;
3131
use rustc_middle::ty::codec::TyEncoder;
3232
use rustc_middle::ty::fast_reject::{self, SimplifiedType, TreatParams};
33+
use rustc_middle::ty::TypeVisitableExt;
3334
use rustc_middle::ty::{self, AssocItemContainer, SymbolName, Ty, TyCtxt};
3435
use rustc_middle::util::common::to_readable_str;
3536
use rustc_serialize::{opaque, Decodable, Decoder, Encodable, Encoder};
@@ -1034,7 +1035,7 @@ fn should_encode_mir(tcx: TyCtxt<'_>, def_id: LocalDefId) -> (bool, bool) {
10341035
}
10351036
}
10361037

1037-
fn should_encode_variances(def_kind: DefKind) -> bool {
1038+
fn should_encode_variances<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId, def_kind: DefKind) -> bool {
10381039
match def_kind {
10391040
DefKind::Struct
10401041
| DefKind::Union
@@ -1053,7 +1054,6 @@ fn should_encode_variances(def_kind: DefKind) -> bool {
10531054
| DefKind::Static(..)
10541055
| DefKind::Const
10551056
| DefKind::ForeignMod
1056-
| DefKind::TyAlias
10571057
| DefKind::Impl { .. }
10581058
| DefKind::Trait
10591059
| DefKind::TraitAlias
@@ -1067,6 +1067,10 @@ fn should_encode_variances(def_kind: DefKind) -> bool {
10671067
| DefKind::Closure
10681068
| DefKind::Generator
10691069
| DefKind::ExternCrate => false,
1070+
DefKind::TyAlias => {
1071+
tcx.features().lazy_type_alias
1072+
|| tcx.type_of(def_id).instantiate_identity().has_opaque_types()
1073+
}
10701074
}
10711075
}
10721076

@@ -1349,7 +1353,7 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
13491353
self.encode_default_body_stability(def_id);
13501354
self.encode_deprecation(def_id);
13511355
}
1352-
if should_encode_variances(def_kind) {
1356+
if should_encode_variances(tcx, def_id, def_kind) {
13531357
let v = self.tcx.variances_of(def_id);
13541358
record_array!(self.tables.variances_of[def_id] <- v);
13551359
}

‎compiler/rustc_middle/src/query/mod.rs

+1-1
Original file line numberDiff line numberDiff line change
@@ -749,7 +749,7 @@ rustc_queries! {
749749
separate_provide_extern
750750
}
751751

752-
/// Gets a map with the variance of every item; use `item_variance` instead.
752+
/// Gets a map with the variance of every item; use `variances_of` instead.
753753
query crate_variances(_: ()) -> &'tcx ty::CrateVariancesMap<'tcx> {
754754
arena_cache
755755
desc { "computing the variances for items in this crate" }

‎tests/ui/lazy-type-alias/variance.rs

+38
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,38 @@
1+
// This is a regression test for issue #114221.
2+
// Check that we compute variances for lazy type aliases.
3+
4+
// check-pass
5+
6+
#![feature(lazy_type_alias)]
7+
#![allow(incomplete_features)]
8+
9+
// [+] `A` is covariant over `'a`.
10+
struct A<'a>(Co<'a>);
11+
12+
// [+] `Co` is covariant over `'a`.
13+
type Co<'a> = &'a ();
14+
15+
fn co<'a>(x: A<'static>) {
16+
let _: A<'a> = x;
17+
}
18+
19+
// [-] `B` is contravariant over `'a`.
20+
struct B<'a>(Contra<'a>);
21+
22+
// [-] `Contra` is contravariant over `'a`.
23+
type Contra<'a> = fn(&'a ());
24+
25+
fn contra<'a>(x: B<'a>) {
26+
let _: B<'static> = x;
27+
}
28+
29+
struct C<T, U>(CoContra<T, U>);
30+
31+
// [+, -] `CoContra` is covariant over `T` and contravariant over `U`.
32+
type CoContra<T, U> = Option<(T, fn(U))>;
33+
34+
fn co_contra<'a>(x: C<&'static (), &'a ()>) -> C<&'a (), &'static ()> {
35+
x
36+
}
37+
38+
fn main() {}

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