Unnamed repository; edit this file 'description' to name the repository.
Diffstat (limited to 'crates/hir-ty/src/variance.rs')
| -rw-r--r-- | crates/hir-ty/src/variance.rs | 90 |
1 files changed, 37 insertions, 53 deletions
diff --git a/crates/hir-ty/src/variance.rs b/crates/hir-ty/src/variance.rs index 5b8122a0a5..6f415a5289 100644 --- a/crates/hir-ty/src/variance.rs +++ b/crates/hir-ty/src/variance.rs @@ -36,13 +36,11 @@ pub(crate) fn variances_of(db: &dyn HirDatabase, def: GenericDefId) -> Variances #[salsa::tracked( returns(ref), - // cycle_fn = crate::variance::variances_of_cycle_fn, - // cycle_initial = crate::variance::variances_of_cycle_initial, - cycle_result = crate::variance::variances_of_cycle_initial, + cycle_fn = crate::variance::variances_of_cycle_fn, + cycle_initial = crate::variance::variances_of_cycle_initial, )] fn variances_of_query(db: &dyn HirDatabase, def: GenericDefId) -> StoredVariancesOf { tracing::debug!("variances_of(def={:?})", def); - let interner = DbInterner::new_no_crate(db); match def { GenericDefId::FunctionId(_) => (), GenericDefId::AdtId(adt) => { @@ -56,43 +54,30 @@ fn variances_of_query(db: &dyn HirDatabase, def: GenericDefId) -> StoredVariance } } } - _ => return VariancesOf::empty(interner).store(), + _ => return VariancesOf::empty(DbInterner::new_no_crate(db)).store(), } let generics = generics(db, def); let count = generics.len(); if count == 0 { - return VariancesOf::empty(interner).store(); - } - let mut variances = - Context { generics, variances: vec![Variance::Bivariant; count], db }.solve(); - - // FIXME(next-solver): This is *not* the correct behavior. I don't know if it has an actual effect, - // since bivariance is prohibited in Rust, but rustc definitely does not fallback bivariance. - // So why do we do this? Because, with the new solver, the effects of bivariance are catastrophic: - // it leads to not relating types properly, and to very, very hard to debug bugs (speaking from experience). - // Furthermore, our variance infra is known to not handle cycles properly. Therefore, at least until we fix - // cycles, and perhaps forever at least for out tests, not allowing bivariance makes sense. - // Why specifically invariance? I don't have a strong reason, mainly that invariance is a stronger relationship - // (therefore, less room for mistakes) and that IMO incorrect covariance can be more problematic that incorrect - // bivariance, at least while we don't handle lifetimes anyway. - for variance in &mut variances { - if *variance == Variance::Bivariant { - *variance = Variance::Invariant; - } + return VariancesOf::empty(DbInterner::new_no_crate(db)).store(); } + let variances = + Context { generics, variances: vec![Variance::Bivariant; count].into_boxed_slice(), db } + .solve(); VariancesOf::new_from_slice(&variances).store() } -// pub(crate) fn variances_of_cycle_fn( -// _db: &dyn HirDatabase, -// _result: &Option<Arc<[Variance]>>, -// _count: u32, -// _def: GenericDefId, -// ) -> salsa::CycleRecoveryAction<Option<Arc<[Variance]>>> { -// salsa::CycleRecoveryAction::Iterate -// } +pub(crate) fn variances_of_cycle_fn( + _db: &dyn HirDatabase, + _: &salsa::Cycle<'_>, + _last_provisional_value: &StoredVariancesOf, + value: StoredVariancesOf, + _def: GenericDefId, +) -> StoredVariancesOf { + value +} fn glb(v1: Variance, v2: Variance) -> Variance { // Greatest lower bound of the variance lattice as defined in The Paper: @@ -123,18 +108,17 @@ pub(crate) fn variances_of_cycle_initial( let generics = generics(db, def); let count = generics.len(); - // FIXME(next-solver): Returns `Invariance` and not `Bivariance` here, see the comment in the main query. - VariancesOf::new_from_iter(interner, std::iter::repeat_n(Variance::Invariant, count)).store() + VariancesOf::new_from_iter(interner, std::iter::repeat_n(Variance::Bivariant, count)).store() } struct Context<'db> { db: &'db dyn HirDatabase, generics: Generics, - variances: Vec<Variance>, + variances: Box<[Variance]>, } impl<'db> Context<'db> { - fn solve(mut self) -> Vec<Variance> { + fn solve(mut self) -> Box<[Variance]> { tracing::debug!("solve(generics={:?})", self.generics); match self.generics.def() { GenericDefId::AdtId(adt) => { @@ -484,8 +468,8 @@ struct Other<'a> { } "#, expect![[r#" - Hello['a: invariant] - Other['a: invariant] + Hello['a: bivariant] + Other['a: bivariant] "#]], ); } @@ -504,7 +488,7 @@ struct Foo<T: Trait> { //~ ERROR [T: o] } "#, expect![[r#" - Foo[T: invariant] + Foo[T: bivariant] "#]], ); } @@ -586,9 +570,9 @@ struct TestBox<U,T:Getter<U>+Setter<U>> { //~ ERROR [U: *, T: +] get[Self: contravariant, T: covariant] get[Self: contravariant, T: contravariant] TestStruct[U: covariant, T: covariant] - TestEnum[U: invariant, T: covariant] - TestContraStruct[U: invariant, T: covariant] - TestBox[U: invariant, T: covariant] + TestEnum[U: bivariant, T: covariant] + TestContraStruct[U: bivariant, T: covariant] + TestBox[U: bivariant, T: covariant] "#]], ); } @@ -708,8 +692,8 @@ enum SomeEnum<'a> { Nothing } //~ ERROR parameter `'a` is never used trait SomeTrait<'a> { fn foo(&self); } // OK on traits. "#, expect![[r#" - SomeStruct['a: invariant] - SomeEnum['a: invariant] + SomeStruct['a: bivariant] + SomeEnum['a: bivariant] foo[Self: contravariant, 'a: invariant] "#]], ); @@ -737,14 +721,14 @@ struct DoubleNothing<T> { "#, expect![[r#" - SomeStruct[A: invariant] - SomeEnum[A: invariant] - ListCell[T: invariant] - SelfTyAlias[T: invariant] - WithBounds[T: invariant] - WithWhereBounds[T: invariant] - WithOutlivesBounds[T: invariant] - DoubleNothing[T: invariant] + SomeStruct[A: bivariant] + SomeEnum[A: bivariant] + ListCell[T: bivariant] + SelfTyAlias[T: bivariant] + WithBounds[T: bivariant] + WithWhereBounds[T: bivariant] + WithOutlivesBounds[T: bivariant] + DoubleNothing[T: bivariant] "#]], ); } @@ -855,7 +839,7 @@ struct S3<T>(S<T, T>); "#, expect![[r#" S[T: covariant] - S2[T: invariant] + S2[T: bivariant] S3[T: covariant] "#]], ); @@ -868,7 +852,7 @@ struct S3<T>(S<T, T>); struct FixedPoint<T, U, V>(&'static FixedPoint<(), T, U>, V); "#, expect![[r#" - FixedPoint[T: invariant, U: invariant, V: invariant] + FixedPoint[T: covariant, U: covariant, V: covariant] "#]], ); } |