bendns' repos / rust-analyzer
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.rs63
1 files changed, 27 insertions, 36 deletions
diff --git a/crates/hir-ty/src/variance.rs b/crates/hir-ty/src/variance.rs
index 64286121b6..30711b16df 100644
--- a/crates/hir-ty/src/variance.rs
+++ b/crates/hir-ty/src/variance.rs
@@ -2,6 +2,16 @@
//! chapter for more info.
//!
//! [rustc dev guide]: https://rustc-dev-guide.rust-lang.org/variance.html
+//!
+//! The implementation here differs from rustc. Rustc does a crate wide fixpoint resolution
+//! as the algorithm for determining variance is a fixpoint computation with potential cycles that
+//! need to be resolved. rust-analyzer does not want a crate-wide analysis though as that would hurt
+//! incrementality too much and as such our query is based on a per item basis.
+//!
+//! This does unfortunately run into the issue that we can run into query cycles which salsa
+//! currently does not allow to be resolved via a fixpoint computation. This will likely be resolved
+//! by the next salsa version. If not, we will likely have to adapt and go with the rustc approach
+//! while installing firewall per item queries to prevent invalidation issues.
use crate::db::HirDatabase;
use crate::generics::{generics, Generics};
@@ -371,33 +381,19 @@ impl Context<'_> {
if args.is_empty() {
return;
}
- if def_id == self.generics.def() {
- // HACK: Workaround for the trivial cycle salsa case (see
- // recursive_one_bivariant_more_non_bivariant_params test)
- for k in args {
- match k.data(Interner) {
- GenericArgData::Lifetime(lt) => {
- self.add_constraints_from_region(lt, Variance::Bivariant)
- }
- GenericArgData::Ty(ty) => self.add_constraints_from_ty(ty, Variance::Bivariant),
- GenericArgData::Const(val) => self.add_constraints_from_const(val, variance),
- }
- }
- } else {
- let Some(variances) = self.db.variances_of(def_id) else {
- return;
- };
+ let Some(variances) = self.db.variances_of(def_id) else {
+ return;
+ };
- for (i, k) in args.iter().enumerate() {
- match k.data(Interner) {
- GenericArgData::Lifetime(lt) => {
- self.add_constraints_from_region(lt, variance.xform(variances[i]))
- }
- GenericArgData::Ty(ty) => {
- self.add_constraints_from_ty(ty, variance.xform(variances[i]))
- }
- GenericArgData::Const(val) => self.add_constraints_from_const(val, variance),
+ for (i, k) in args.iter().enumerate() {
+ match k.data(Interner) {
+ GenericArgData::Lifetime(lt) => {
+ self.add_constraints_from_region(lt, variance.xform(variances[i]))
+ }
+ GenericArgData::Ty(ty) => {
+ self.add_constraints_from_ty(ty, variance.xform(variances[i]))
}
+ GenericArgData::Const(val) => self.add_constraints_from_const(val, variance),
}
}
}
@@ -956,22 +952,17 @@ struct S3<T>(S<T, T>);
}
#[test]
- fn recursive_one_bivariant_more_non_bivariant_params() {
- // FIXME: This is wrong, this should be `BivariantPartialIndirect[T: bivariant, U: covariant]` (likewise for Wrapper)
+ fn prove_fixedpoint() {
+ // FIXME: This is wrong, this should be `FixedPoint[T: covariant, U: covariant, V: covariant]`
// This is a limitation of current salsa where a cycle may only set a fallback value to the
- // query result which is not what we want! We want to treat the cycle call as fallback
- // without setting the query result to the fallback.
- // `BivariantPartial` works as we workaround for the trivial case of being self-referential
+ // query result, but we need to solve a fixpoint here. The new salsa will have this
+ // fortunately.
check(
r#"
-struct BivariantPartial<T, U>(*const BivariantPartial<T, U>, U);
-struct Wrapper<T, U>(BivariantPartialIndirect<T, U>);
-struct BivariantPartialIndirect<T, U>(*const Wrapper<T, U>, U);
+struct FixedPoint<T, U, V>(&'static FixedPoint<(), T, U>, V);
"#,
expect![[r#"
- BivariantPartial[T: bivariant, U: covariant]
- Wrapper[T: bivariant, U: bivariant]
- BivariantPartialIndirect[T: bivariant, U: bivariant]
+ FixedPoint[T: bivariant, U: bivariant, V: bivariant]
"#]],
);
}