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Rollup merge of #114253 - fmease:compute-variances-for-lazy-ty-aliases, r=oli-obk 

Compute variances for lazy type aliases

Fixes #114221.

CC ``@oli-obk``
r? types
This commit is contained in:
Matthias Krüger 2023-08-04 09:18:58 +02:00 committed by GitHub
parent 576bf82702 6f5d8556ca
commit 5ea536b35f
No known key found for this signature in database
GPG Key ID: 4AEE18F83AFDEB23
22 changed files with 226 additions and 85 deletions
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26
compiler/rustc_hir_analysis/src/check/wfcheck.rs
View File

@ -245,13 +245,14 @@ fn check_item<'tcx>(tcx: TyCtxt<'tcx>, item: &'tcx hir::Item<'tcx>) {
}
// `ForeignItem`s are handled separately.
hir::ItemKind::ForeignMod { .. } => {}
hir::ItemKind::TyAlias(hir_ty, ..) => {
hir::ItemKind::TyAlias(hir_ty, ast_generics) => {
if tcx.features().lazy_type_alias
|| tcx.type_of(item.owner_id).skip_binder().has_opaque_types()
{
// Bounds of lazy type aliases and of eager ones that contain opaque types are respected.
// E.g: `type X = impl Trait;`, `type X = (impl Trait, Y);`.
check_item_type(tcx, def_id, hir_ty.span, UnsizedHandling::Allow);
check_variances_for_type_defn(tcx, item, ast_generics);
}
}
_ => {}
@ -1700,10 +1701,27 @@ fn check_variances_for_type_defn<'tcx>(
hir_generics: &hir::Generics<'_>,
) {
let identity_args = ty::GenericArgs::identity_for_item(tcx, item.owner_id);
for field in tcx.adt_def(item.owner_id).all_fields() {
if field.ty(tcx, identity_args).references_error() {
return;
match item.kind {
ItemKind::Enum(..) | ItemKind::Struct(..) | ItemKind::Union(..) => {
for field in tcx.adt_def(item.owner_id).all_fields() {
if field.ty(tcx, identity_args).references_error() {
return;
}
}
}
ItemKind::TyAlias(..) => {
let ty = tcx.type_of(item.owner_id).instantiate_identity();
if tcx.features().lazy_type_alias || ty.has_opaque_types() {
if ty.references_error() {
return;
}
} else {
bug!();
}
}
_ => bug!(),
}
let ty_predicates = tcx.predicates_of(item.owner_id);

28
compiler/rustc_hir_analysis/src/variance/constraints.rs
View File

@ -6,7 +6,7 @@
use hir::def_id::{DefId, LocalDefId};
use rustc_hir as hir;
use rustc_hir::def::DefKind;
use rustc_middle::ty::{self, Ty, TyCtxt};
use rustc_middle::ty::{self, Ty, TyCtxt, TypeVisitableExt};
use rustc_middle::ty::{GenericArgKind, GenericArgsRef};
use super::terms::VarianceTerm::*;
@ -78,6 +78,12 @@ pub fn add_constraints_from_crate<'a, 'tcx>(
}
}
DefKind::Fn | DefKind::AssocFn => constraint_cx.build_constraints_for_item(def_id),
DefKind::TyAlias
if tcx.features().lazy_type_alias
|| tcx.type_of(def_id).instantiate_identity().has_opaque_types() =>
{
constraint_cx.build_constraints_for_item(def_id)
}
_ => {}
}
}
@ -101,7 +107,18 @@ impl<'a, 'tcx> ConstraintContext<'a, 'tcx> {
let inferred_start = self.terms_cx.inferred_starts[&def_id];
let current_item = &CurrentItem { inferred_start };
match tcx.type_of(def_id).instantiate_identity().kind() {
let ty = tcx.type_of(def_id).instantiate_identity();
// The type as returned by `type_of` is the underlying type and generally not a weak projection.
// Therefore we need to check the `DefKind` first.
if let DefKind::TyAlias = tcx.def_kind(def_id)
&& (tcx.features().lazy_type_alias || ty.has_opaque_types())
{
self.add_constraints_from_ty(current_item, ty, self.covariant);
return;
}
match ty.kind() {
ty::Adt(def, _) => {
// Not entirely obvious: constraints on structs/enums do not
// affect the variance of their type parameters. See discussion
@ -127,6 +144,7 @@ impl<'a, 'tcx> ConstraintContext<'a, 'tcx> {
}
ty::Error(_) => {}
_ => {
span_bug!(
tcx.def_span(def_id),
@ -252,10 +270,14 @@ impl<'a, 'tcx> ConstraintContext<'a, 'tcx> {
self.add_constraints_from_args(current, def.did(), args, variance);
}
ty::Alias(_, ref data) => {
ty::Alias(ty::Projection | ty::Inherent | ty::Opaque, ref data) => {
self.add_constraints_from_invariant_args(current, data.args, variance);
}
ty::Alias(ty::Weak, ref data) => {
self.add_constraints_from_args(current, data.def_id, data.args, variance);
}
ty::Dynamic(data, r, _) => {
// The type `dyn Trait<T> +'a` is covariant w/r/t `'a`:
self.add_constraints_from_region(current, r, variance);

10
compiler/rustc_hir_analysis/src/variance/mod.rs
View File

@ -8,7 +8,7 @@ use rustc_hir::def::DefKind;
use rustc_hir::def_id::{DefId, LocalDefId};
use rustc_middle::query::Providers;
use rustc_middle::ty::{self, CrateVariancesMap, GenericArgsRef, Ty, TyCtxt};
use rustc_middle::ty::{TypeSuperVisitable, TypeVisitable};
use rustc_middle::ty::{TypeSuperVisitable, TypeVisitable, TypeVisitableExt};
use std::ops::ControlFlow;
/// 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] {
let crate_map = tcx.crate_variances(());
return crate_map.variances.get(&item_def_id.to_def_id()).copied().unwrap_or(&[]);
}
DefKind::TyAlias
if tcx.features().lazy_type_alias
|| tcx.type_of(item_def_id).instantiate_identity().has_opaque_types() =>
{
// These are inferred.
let crate_map = tcx.crate_variances(());
return crate_map.variances.get(&item_def_id.to_def_id()).copied().unwrap_or(&[]);
}
DefKind::OpaqueTy => {
return variance_of_opaque(tcx, item_def_id);
}

8
compiler/rustc_hir_analysis/src/variance/terms.rs
View File

@ -12,7 +12,7 @@
use rustc_arena::DroplessArena;
use rustc_hir::def::DefKind;
use rustc_hir::def_id::{LocalDefId, LocalDefIdMap};
use rustc_middle::ty::{self, TyCtxt};
use rustc_middle::ty::{self, TyCtxt, TypeVisitableExt};
use std::fmt;
use self::VarianceTerm::*;
@ -97,6 +97,12 @@ pub fn determine_parameters_to_be_inferred<'a, 'tcx>(
}
}
DefKind::Fn | DefKind::AssocFn => terms_cx.add_inferreds_for_item(def_id),
DefKind::TyAlias
if tcx.features().lazy_type_alias
|| tcx.type_of(def_id).instantiate_identity().has_opaque_types() =>
{
terms_cx.add_inferreds_for_item(def_id)
}
_ => {}
}
}

10
compiler/rustc_metadata/src/rmeta/encoder.rs
View File

@ -30,6 +30,7 @@ use rustc_middle::query::Providers;
use rustc_middle::traits::specialization_graph;
use rustc_middle::ty::codec::TyEncoder;
use rustc_middle::ty::fast_reject::{self, SimplifiedType, TreatParams};
use rustc_middle::ty::TypeVisitableExt;
use rustc_middle::ty::{self, AssocItemContainer, SymbolName, Ty, TyCtxt};
use rustc_middle::util::common::to_readable_str;
use rustc_serialize::{opaque, Decodable, Decoder, Encodable, Encoder};
@ -1034,7 +1035,7 @@ fn should_encode_mir(tcx: TyCtxt<'_>, def_id: LocalDefId) -> (bool, bool) {
}
}
fn should_encode_variances(def_kind: DefKind) -> bool {
fn should_encode_variances<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId, def_kind: DefKind) -> bool {
match def_kind {
DefKind::Struct
| DefKind::Union
@ -1053,7 +1054,6 @@ fn should_encode_variances(def_kind: DefKind) -> bool {
| DefKind::Static(..)
| DefKind::Const
| DefKind::ForeignMod
| DefKind::TyAlias
| DefKind::Impl { .. }
| DefKind::Trait
| DefKind::TraitAlias
@ -1067,6 +1067,10 @@ fn should_encode_variances(def_kind: DefKind) -> bool {
| DefKind::Closure
| DefKind::Generator
| DefKind::ExternCrate => false,
DefKind::TyAlias => {
tcx.features().lazy_type_alias
|| tcx.type_of(def_id).instantiate_identity().has_opaque_types()
}
}
}
@ -1349,7 +1353,7 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
self.encode_default_body_stability(def_id);
self.encode_deprecation(def_id);
}
if should_encode_variances(def_kind) {
if should_encode_variances(tcx, def_id, def_kind) {
let v = self.tcx.variances_of(def_id);
record_array!(self.tables.variances_of[def_id] <- v);
}

2
compiler/rustc_middle/src/query/mod.rs
View File

@ -749,7 +749,7 @@ rustc_queries! {
separate_provide_extern
}
/// Gets a map with the variance of every item; use `item_variance` instead.
/// Gets a map with the variance of every item; use `variances_of` instead.
query crate_variances(_: ()) -> &'tcx ty::CrateVariancesMap<'tcx> {
arena_cache
desc { "computing the variances for items in this crate" }

17
tests/rustdoc-json/type/inherent_associated_type_bound.rs
View File

@ -5,14 +5,15 @@
// @set Carrier = '$.index[*][?(@.name=="Carrier")].id'
pub struct Carrier<'a>(&'a ());
// @is '$.index[*][?(@.name=="User")].inner.typedef.type.function_pointer.generic_params[*].name' \""'b"\"
// @is '$.index[*][?(@.name=="User")].inner.typedef.type.function_pointer.decl.inputs[0][1].qualified_path.self_type.resolved_path.id' $Carrier
// @is '$.index[*][?(@.name=="User")].inner.typedef.type.function_pointer.decl.inputs[0][1].qualified_path.self_type.resolved_path.args.angle_bracketed.args[0].lifetime' \""'b"\"
// @is '$.index[*][?(@.name=="User")].inner.typedef.type.function_pointer.decl.inputs[0][1].qualified_path.name' '"Focus"'
// @is '$.index[*][?(@.name=="User")].inner.typedef.type.function_pointer.decl.inputs[0][1].qualified_path.trait' null
// @is '$.index[*][?(@.name=="User")].inner.typedef.type.function_pointer.decl.inputs[0][1].qualified_path.args.angle_bracketed.args[0].type.primitive' '"i32"'
pub type User = for<'b> fn(Carrier<'b>::Focus<i32>);
// @count "$.index[*][?(@.name=='user')].inner.function.decl.inputs[*]" 1
// @is "$.index[*][?(@.name=='user')].inner.function.decl.inputs[0][0]" '"_"'
// @is '$.index[*][?(@.name=="user")].inner.function.decl.inputs[0][1].function_pointer.generic_params[*].name' \""'b"\"
// @is '$.index[*][?(@.name=="user")].inner.function.decl.inputs[0][1].function_pointer.decl.inputs[0][1].qualified_path.self_type.resolved_path.id' $Carrier
// @is '$.index[*][?(@.name=="user")].inner.function.decl.inputs[0][1].function_pointer.decl.inputs[0][1].qualified_path.self_type.resolved_path.args.angle_bracketed.args[0].lifetime' \""'b"\"
// @is '$.index[*][?(@.name=="user")].inner.function.decl.inputs[0][1].function_pointer.decl.inputs[0][1].qualified_path.name' '"Focus"'
// @is '$.index[*][?(@.name=="user")].inner.function.decl.inputs[0][1].function_pointer.decl.inputs[0][1].qualified_path.trait' null
// @is '$.index[*][?(@.name=="user")].inner.function.decl.inputs[0][1].function_pointer.decl.inputs[0][1].qualified_path.args.angle_bracketed.args[0].type.primitive' '"i32"'
pub fn user(_: for<'b> fn(Carrier<'b>::Focus<i32>)) {}
impl<'a> Carrier<'a> {
pub type Focus<T> = &'a mut T;

12
tests/rustdoc-json/type/inherent_associated_type_projections.rs
View File

@ -5,11 +5,13 @@
// @set Parametrized = '$.index[*][?(@.name=="Parametrized")].id'
pub struct Parametrized<T>(T);
// @is '$.index[*][?(@.name=="Test")].inner.typedef.type.qualified_path.self_type.resolved_path.id' $Parametrized
// @is '$.index[*][?(@.name=="Test")].inner.typedef.type.qualified_path.self_type.resolved_path.args.angle_bracketed.args[0].type.primitive' \"i32\"
// @is '$.index[*][?(@.name=="Test")].inner.typedef.type.qualified_path.name' '"Proj"'
// @is '$.index[*][?(@.name=="Test")].inner.typedef.type.qualified_path.trait' null
pub type Test = Parametrized<i32>::Proj;
// @count "$.index[*][?(@.name=='test')].inner.function.decl.inputs[*]" 1
// @is "$.index[*][?(@.name=='test')].inner.function.decl.inputs[0][0]" '"_"'
// @is '$.index[*][?(@.name=="test")].inner.function.decl.inputs[0][1].qualified_path.self_type.resolved_path.id' $Parametrized
// @is '$.index[*][?(@.name=="test")].inner.function.decl.inputs[0][1].qualified_path.self_type.resolved_path.args.angle_bracketed.args[0].type.primitive' \"i32\"
// @is '$.index[*][?(@.name=="test")].inner.function.decl.inputs[0][1].qualified_path.name' '"Proj"'
// @is '$.index[*][?(@.name=="test")].inner.function.decl.inputs[0][1].qualified_path.trait' null
pub fn test(_: Parametrized<i32>::Proj) {}
/// param_bool
impl Parametrized<bool> {

10
tests/rustdoc/inherent-projections.rs
View File

@ -13,8 +13,8 @@ impl Owner {
}
// Make sure we handle bound vars correctly.
// @has 'inherent_projections/type.User.html' '//pre[@class="rust item-decl"]' "for<'a> fn(_: Carrier<'a>::Focus)"
pub type User = for<'a> fn(Carrier<'a>::Focus);
// @has 'inherent_projections/fn.user.html' '//pre[@class="rust item-decl"]' "user(_: for<'a> fn(_: Carrier<'a>::Focus))"
pub fn user(_: for<'a> fn(Carrier<'a>::Focus)) {}
pub struct Carrier<'a>(&'a ());
@ -27,11 +27,11 @@ impl<'a> Carrier<'a> {
// FIXME(inherent_associated_types): Below we link to `Proj` but we should link to `Proj-1`.
// The current test checks for the buggy behavior for demonstration purposes.
// @has 'inherent_projections/type.Test.html'
// @has - '//pre[@class="rust item-decl"]' "Parametrized<i32>"
// @has 'inherent_projections/fn.test.html'
// @has - '//pre[@class="rust item-decl"]' "test(_: Parametrized<i32>::Proj)"
// @has - '//pre[@class="rust item-decl"]//a[@class="associatedtype"]/@href' 'struct.Parametrized.html#associatedtype.Proj'
// @!has - '//pre[@class="rust item-decl"]//a[@class="associatedtype"]/@href' 'struct.Parametrized.html#associatedtype.Proj-1'
pub type Test = Parametrized<i32>::Proj;
pub fn test(_: Parametrized<i32>::Proj) {}
pub struct Parametrized<T>(T);

4
tests/ui/associated-inherent-types/issue-111879-0.rs
View File

@ -5,10 +5,8 @@
pub struct Carrier<'a>(&'a ());
pub type User = for<'b> fn(Carrier<'b>::Focus<i32>);
impl<'a> Carrier<'a> {
pub type Focus<T> = &'a mut User; //~ ERROR overflow evaluating associated type
pub type Focus<T> = &'a mut for<'b> fn(Carrier<'b>::Focus<i32>); //~ ERROR overflow evaluating associated type
}
fn main() {}

6
tests/ui/associated-inherent-types/issue-111879-0.stderr
View File

@ -1,8 +1,8 @@
error: overflow evaluating associated type `Carrier<'b>::Focus<i32>`
--> $DIR/issue-111879-0.rs:11:25
--> $DIR/issue-111879-0.rs:9:25
|
LL | pub type Focus<T> = &'a mut User;
| ^^^^^^^^^^^^
LL | pub type Focus<T> = &'a mut for<'b> fn(Carrier<'b>::Focus<i32>);
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
error: aborting due to previous error

4
tests/ui/associated-inherent-types/late-bound-regions.rs
View File

@ -3,8 +3,6 @@
// Test if we correctly normalize `S<'a>::P` with respect to late-bound regions.
type Function = for<'a> fn(&'a i32) -> S<'a>::P;
struct S<'a>(&'a ());
trait Inter {
@ -16,7 +14,7 @@ impl<'a> S<'a> {
}
fn ret_ref_local<'e>() -> &'e i32 {
let f: Function = |x| x;
let f: for<'a> fn(&'a i32) -> S<'a>::P = |x| x;
let local = 0;
f(&local) //~ ERROR cannot return value referencing local variable `local`

2
tests/ui/associated-inherent-types/late-bound-regions.stderr
View File

@ -1,5 +1,5 @@
error[E0515]: cannot return value referencing local variable `local`
--> $DIR/late-bound-regions.rs:22:5
--> $DIR/late-bound-regions.rs:20:5
|
LL | f(&local)
| ^^------^

16
tests/ui/associated-inherent-types/not-found-self-type-differs.alias.stderr
View File

@ -1,16 +0,0 @@
error[E0220]: associated type `Proj` not found for `Family<Option<()>>` in the current scope
--> $DIR/not-found-self-type-differs.rs:17:34
|
LL | struct Family<T>(T);
| ---------------- associated item `Proj` not found for this struct
...
LL | type Alias = Family<Option<()>>::Proj;
| ^^^^ associated item not found in `Family<Option<()>>`
|
= note: the associated type was found for
- `Family<()>`
- `Family<Result<T, ()>>`
error: aborting due to previous error
For more information about this error, try `rustc --explain E0220`.

16
tests/ui/associated-inherent-types/not-found-self-type-differs.local.stderr
View File

@ -1,16 +0,0 @@
error[E0220]: associated type `Proj` not found for `Family<PathBuf>` in the current scope
--> $DIR/not-found-self-type-differs.rs:21:40
|
LL | struct Family<T>(T);
| ---------------- associated item `Proj` not found for this struct
...
LL | let _: Family<std::path::PathBuf>::Proj = ();
| ^^^^ associated item not found in `Family<PathBuf>`
|
= note: the associated type was found for
- `Family<()>`
- `Family<Result<T, ()>>`
error: aborting due to previous error
For more information about this error, try `rustc --explain E0220`.

9
tests/ui/associated-inherent-types/not-found-self-type-differs.rs
View File

@ -1,5 +1,3 @@
// revisions: local alias
#![feature(inherent_associated_types)]
#![allow(incomplete_features)]
@ -13,10 +11,7 @@ impl<T> Family<Result<T, ()>> {
type Proj = Self;
}
#[cfg(alias)]
type Alias = Family<Option<()>>::Proj; //[alias]~ ERROR associated type `Proj` not found for `Family<Option<()>>`
fn main() {
#[cfg(local)]
let _: Family<std::path::PathBuf>::Proj = (); //[local]~ ERROR associated type `Proj` not found for `Family<PathBuf>`
let _: Family<Option<()>>::Proj; //~ ERROR associated type `Proj` not found for `Family<Option<()>>`
let _: Family<std::path::PathBuf>::Proj = (); //~ ERROR associated type `Proj` not found for `Family<PathBuf>`
}

29
tests/ui/associated-inherent-types/not-found-self-type-differs.stderr Normal file
View File

@ -0,0 +1,29 @@
error[E0220]: associated type `Proj` not found for `Family<Option<()>>` in the current scope
--> $DIR/not-found-self-type-differs.rs:15:32
|
LL | struct Family<T>(T);
| ---------------- associated item `Proj` not found for this struct
...
LL | let _: Family<Option<()>>::Proj;
| ^^^^ associated item not found in `Family<Option<()>>`
|
= note: the associated type was found for
- `Family<()>`
- `Family<Result<T, ()>>`
error[E0220]: associated type `Proj` not found for `Family<PathBuf>` in the current scope
--> $DIR/not-found-self-type-differs.rs:16:40
|
LL | struct Family<T>(T);
| ---------------- associated item `Proj` not found for this struct
...
LL | let _: Family<std::path::PathBuf>::Proj = ();
| ^^^^ associated item not found in `Family<PathBuf>`
|
= note: the associated type was found for
- `Family<()>`
- `Family<Result<T, ()>>`
error: aborting due to 2 previous errors
For more information about this error, try `rustc --explain E0220`.

2
tests/ui/associated-inherent-types/substitute-params-bad.rs
View File

@ -17,7 +17,7 @@ impl<T, S> Subj<(T, S)> {
}
fn main() {
type A = S<()>::P;
let _: S<()>::P;
let _: Subj<(i32, i32)>::Un = 0i32; //~ ERROR mismatched types
}

3
tests/ui/associated-inherent-types/substitute-params.rs
View File

@ -15,8 +15,7 @@ impl<T> S<(T,)> {
fn main() {
// Regression test for issue #104240.
type A = S<()>::P;
let _: A = ();
let _: S<()>::P = ();
// Regression test for issue #107468.
let _: S<(i32,)>::Un = 0i32;

4
tests/ui/associated-inherent-types/type-alias-bounds-are-enforced.rs
View File

@ -1,4 +1,5 @@
// check-pass
// FIXME(inherent_associated_types): This should be `check-pass`
// known-bug: #108491
// compile-flags: --crate-type=lib
#![feature(inherent_associated_types)]
@ -17,7 +18,6 @@
pub type Alias<T: Bound> = (Source<T>::Assoc,);
pub struct Source<T>(T);
pub trait Bound {}

55
tests/ui/associated-inherent-types/type-alias-bounds-are-enforced.stderr Normal file
View File

@ -0,0 +1,55 @@
error[E0391]: cycle detected when expanding type alias `Alias`
--> $DIR/type-alias-bounds-are-enforced.rs:19:1
|
LL | pub type Alias<T: Bound> = (Source<T>::Assoc,);
| ^^^^^^^^^^^^^^^^^^^^^^^^
|
note: ...which requires computing the variances of `Source`...
--> $DIR/type-alias-bounds-are-enforced.rs:21:1
|
LL | pub struct Source<T>(T);
| ^^^^^^^^^^^^^^^^^^^^
= note: ...which requires computing the variances for items in this crate...
= note: ...which again requires expanding type alias `Alias`, completing the cycle
note: cycle used when collecting item types in top-level module
--> $DIR/type-alias-bounds-are-enforced.rs:5:1
|
LL | / #![feature(inherent_associated_types)]
LL | | #![allow(incomplete_features)]
LL | |
LL | | // Bounds on the self type play a major role in the resolution of inherent associated types (*).
... |
LL | | pub type Assoc = ();
LL | | }
| |_^
= note: see https://rustc-dev-guide.rust-lang.org/overview.html#queries and https://rustc-dev-guide.rust-lang.org/query.html for more information
error[E0391]: cycle detected when expanding type alias `Alias`
--> $DIR/type-alias-bounds-are-enforced.rs:19:1
|
LL | pub type Alias<T: Bound> = (Source<T>::Assoc,);
| ^^^^^^^^^^^^^^^^^^^^^^^^
|
note: ...which requires computing the variances of `Source`...
--> $DIR/type-alias-bounds-are-enforced.rs:21:1
|
LL | pub struct Source<T>(T);
| ^^^^^^^^^^^^^^^^^^^^
= note: ...which requires computing the variances for items in this crate...
= note: ...which again requires expanding type alias `Alias`, completing the cycle
note: cycle used when collecting item types in top-level module
--> $DIR/type-alias-bounds-are-enforced.rs:5:1
|
LL | / #![feature(inherent_associated_types)]
LL | | #![allow(incomplete_features)]
LL | |
LL | | // Bounds on the self type play a major role in the resolution of inherent associated types (*).
... |
LL | | pub type Assoc = ();
LL | | }
| |_^
= note: see https://rustc-dev-guide.rust-lang.org/overview.html#queries and https://rustc-dev-guide.rust-lang.org/query.html for more information
error: aborting due to 2 previous errors
For more information about this error, try `rustc --explain E0391`.

38
tests/ui/lazy-type-alias/variance.rs Normal file
View File

@ -0,0 +1,38 @@
// This is a regression test for issue #114221.
// Check that we compute variances for lazy type aliases.
// check-pass
#![feature(lazy_type_alias)]
#![allow(incomplete_features)]
// [+] `A` is covariant over `'a`.
struct A<'a>(Co<'a>);
// [+] `Co` is covariant over `'a`.
type Co<'a> = &'a ();
fn co<'a>(x: A<'static>) {
let _: A<'a> = x;
}
// [-] `B` is contravariant over `'a`.
struct B<'a>(Contra<'a>);
// [-] `Contra` is contravariant over `'a`.
type Contra<'a> = fn(&'a ());
fn contra<'a>(x: B<'a>) {
let _: B<'static> = x;
}
struct C<T, U>(CoContra<T, U>);
// [+, -] `CoContra` is covariant over `T` and contravariant over `U`.
type CoContra<T, U> = Option<(T, fn(U))>;
fn co_contra<'a>(x: C<&'static (), &'a ()>) -> C<&'a (), &'static ()> {
x
}
fn main() {}