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Make nll higher ranked equate use bidirectional subtyping in invariant context
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0479287a38
@ -483,61 +483,59 @@ impl<'bccx, 'tcx> TypeRelation<'tcx> for NllTypeRelating<'_, 'bccx, 'tcx> {
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return Ok(ty::Binder::dummy(a));
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}
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if self.ambient_covariance() {
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// Covariance, so we want `for<..> A <: for<..> B` --
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// therefore we compare any instantiation of A (i.e., A
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// instantiated with existentials) against every
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// instantiation of B (i.e., B instantiated with
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// universals).
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match self.ambient_variance {
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ty::Variance::Covariant => {
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// Covariance, so we want `for<..> A <: for<..> B` --
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// therefore we compare any instantiation of A (i.e., A
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// instantiated with existentials) against every
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// instantiation of B (i.e., B instantiated with
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// universals).
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// Reset the ambient variance to covariant. This is needed
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// to correctly handle cases like
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//
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// for<'a> fn(&'a u32, &'a u32) == for<'b, 'c> fn(&'b u32, &'c u32)
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//
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// Somewhat surprisingly, these two types are actually
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// **equal**, even though the one on the right looks more
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// polymorphic. The reason is due to subtyping. To see it,
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// consider that each function can call the other:
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//
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// - The left function can call the right with `'b` and
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// `'c` both equal to `'a`
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//
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// - The right function can call the left with `'a` set to
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// `{P}`, where P is the point in the CFG where the call
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// itself occurs. Note that `'b` and `'c` must both
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// include P. At the point, the call works because of
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// subtyping (i.e., `&'b u32 <: &{P} u32`).
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let variance = std::mem::replace(&mut self.ambient_variance, ty::Variance::Covariant);
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// Note: the order here is important. Create the placeholders first, otherwise
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// we assign the wrong universe to the existential!
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self.enter_forall(b, |this, b| {
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let a = this.instantiate_binder_with_existentials(a);
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this.relate(a, b)
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})?;
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}
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// Note: the order here is important. Create the placeholders first, otherwise
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// we assign the wrong universe to the existential!
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self.enter_forall(b, |this, b| {
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let a = this.instantiate_binder_with_existentials(a);
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this.relate(a, b)
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})?;
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ty::Variance::Contravariant => {
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// Contravariance, so we want `for<..> A :> for<..> B` --
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// therefore we compare every instantiation of A (i.e., A
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// instantiated with universals) against any
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// instantiation of B (i.e., B instantiated with
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// existentials). Opposite of above.
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self.ambient_variance = variance;
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}
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// Note: the order here is important. Create the placeholders first, otherwise
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// we assign the wrong universe to the existential!
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self.enter_forall(a, |this, a| {
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let b = this.instantiate_binder_with_existentials(b);
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this.relate(a, b)
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})?;
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}
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if self.ambient_contravariance() {
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// Contravariance, so we want `for<..> A :> for<..> B`
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// -- therefore we compare every instantiation of A (i.e.,
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// A instantiated with universals) against any
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// instantiation of B (i.e., B instantiated with
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// existentials). Opposite of above.
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ty::Variance::Invariant => {
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// Invariant, so we want `for<..> A == for<..> B` --
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// therefore we want `exists<..> A == for<..> B` and
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// `exists<..> B == for<..> A`.
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//
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// See the comment in `fn Equate::binders` for more details.
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// Reset ambient variance to contravariance. See the
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// covariant case above for an explanation.
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let variance =
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std::mem::replace(&mut self.ambient_variance, ty::Variance::Contravariant);
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// Note: the order here is important. Create the placeholders first, otherwise
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// we assign the wrong universe to the existential!
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self.enter_forall(b, |this, b| {
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let a = this.instantiate_binder_with_existentials(a);
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this.relate(a, b)
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})?;
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// Note: the order here is important. Create the placeholders first, otherwise
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// we assign the wrong universe to the existential!
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self.enter_forall(a, |this, a| {
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let b = this.instantiate_binder_with_existentials(b);
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this.relate(a, b)
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})?;
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}
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self.enter_forall(a, |this, a| {
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let b = this.instantiate_binder_with_existentials(b);
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this.relate(a, b)
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})?;
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self.ambient_variance = variance;
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ty::Variance::Bivariant => {}
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}
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Ok(a)
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@ -30,14 +30,16 @@ fn expect_free_supply_bound() {
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// Here, we are given a function whose region is bound at closure level,
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// but we expect one bound in the argument. Error results.
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with_closure_expecting_fn_with_free_region(|x: fn(&u32), y| {});
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//~^ ERROR mismatched types
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//~^ ERROR mismatched types [E0308]
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//~| ERROR lifetime may not live long enough
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}
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fn expect_bound_supply_free_from_fn<'x>(x: &'x u32) {
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// Here, we are given a `fn(&u32)` but we expect a `fn(&'x
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// u32)`. In principle, this could be ok, but we demand equality.
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with_closure_expecting_fn_with_bound_region(|x: fn(&'x u32), y| {});
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//~^ ERROR mismatched types
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//~^ ERROR mismatched types [E0308]
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//~| ERROR lifetime may not live long enough
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}
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fn expect_bound_supply_free_from_closure() {
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@ -19,6 +19,15 @@ LL | fn expect_free_supply_free_from_fn<'x>(x: &'x u32) {
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LL | with_closure_expecting_fn_with_free_region(|x: fn(&'x u32), y| {});
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| ^ requires that `'x` must outlive `'static`
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error: lifetime may not live long enough
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--> $DIR/expect-fn-supply-fn.rs:32:49
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LL | with_closure_expecting_fn_with_free_region(|x: fn(&u32), y| {});
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| ^
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| |
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| has type `fn(&'1 u32)`
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| requires that `'1` must outlive `'static`
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error[E0308]: mismatched types
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--> $DIR/expect-fn-supply-fn.rs:32:49
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@ -29,7 +38,7 @@ LL | with_closure_expecting_fn_with_free_region(|x: fn(&u32), y| {});
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found fn pointer `for<'a> fn(&'a _)`
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error[E0308]: mismatched types
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--> $DIR/expect-fn-supply-fn.rs:39:50
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--> $DIR/expect-fn-supply-fn.rs:40:50
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LL | with_closure_expecting_fn_with_bound_region(|x: fn(&'x u32), y| {});
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| ^ one type is more general than the other
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@ -37,8 +46,17 @@ LL | with_closure_expecting_fn_with_bound_region(|x: fn(&'x u32), y| {});
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= note: expected fn pointer `for<'a> fn(&'a _)`
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found fn pointer `fn(&_)`
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error: lifetime may not live long enough
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--> $DIR/expect-fn-supply-fn.rs:40:50
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LL | fn expect_bound_supply_free_from_fn<'x>(x: &'x u32) {
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| -- lifetime `'x` defined here
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...
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LL | with_closure_expecting_fn_with_bound_region(|x: fn(&'x u32), y| {});
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| ^ requires that `'x` must outlive `'static`
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error[E0308]: mismatched types
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--> $DIR/expect-fn-supply-fn.rs:48:50
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--> $DIR/expect-fn-supply-fn.rs:50:50
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LL | with_closure_expecting_fn_with_bound_region(|x: Foo<'_>, y| {
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| ^ one type is more general than the other
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@ -46,6 +64,6 @@ LL | with_closure_expecting_fn_with_bound_region(|x: Foo<'_>, y| {
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= note: expected fn pointer `for<'a> fn(&'a _)`
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found fn pointer `fn(&_)`
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error: aborting due to 5 previous errors
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error: aborting due to 7 previous errors
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For more information about this error, try `rustc --explain E0308`.
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tests/ui/higher-ranked/higher-ranked-lifetime-equality.rs
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38
tests/ui/higher-ranked/higher-ranked-lifetime-equality.rs
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@ -0,0 +1,38 @@
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// A regression test for #97156
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type One = for<'a> fn(&'a (), &'a ());
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type Two = for<'a, 'b> fn(&'a (), &'b ());
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mod my_api {
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use std::any::Any;
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use std::marker::PhantomData;
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pub struct Foo<T: 'static> {
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a: &'static dyn Any,
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_p: PhantomData<*mut T>, // invariant, the type of the `dyn Any`
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}
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impl<T: 'static> Foo<T> {
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pub fn deref(&self) -> &'static T {
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match self.a.downcast_ref::<T>() {
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None => unsafe { std::hint::unreachable_unchecked() },
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Some(a) => a,
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}
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}
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pub fn new(a: T) -> Foo<T> {
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Foo::<T> { a: Box::leak(Box::new(a)), _p: PhantomData }
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}
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}
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}
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use my_api::*;
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fn main() {
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let foo = Foo::<One>::new((|_, _| ()) as One);
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foo.deref();
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let foo: Foo<Two> = foo;
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//~^ ERROR mismatched types [E0308]
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//~| ERROR mismatched types [E0308]
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foo.deref();
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}
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@ -0,0 +1,22 @@
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error[E0308]: mismatched types
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--> $DIR/higher-ranked-lifetime-equality.rs:34:25
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LL | let foo: Foo<Two> = foo;
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| ^^^ one type is more general than the other
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= note: expected struct `my_api::Foo<for<'a, 'b> fn(&'a (), &'b ())>`
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found struct `my_api::Foo<for<'a> fn(&'a (), &'a ())>`
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error[E0308]: mismatched types
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--> $DIR/higher-ranked-lifetime-equality.rs:34:25
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LL | let foo: Foo<Two> = foo;
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| ^^^ one type is more general than the other
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= note: expected struct `my_api::Foo<for<'a, 'b> fn(&'a (), &'b ())>`
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found struct `my_api::Foo<for<'a> fn(&'a (), &'a ())>`
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= note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
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error: aborting due to 2 previous errors
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For more information about this error, try `rustc --explain E0308`.
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@ -6,7 +6,6 @@
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// another -- effectively, the single lifetime `'a` is just inferred
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// to be the intersection of the two distinct lifetimes.
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//
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//@ check-pass
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//@ compile-flags:-Zno-leak-check
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use std::cell::Cell;
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@ -17,7 +16,9 @@ fn make_cell_aa() -> Cell<for<'a> fn(&'a u32, &'a u32)> {
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fn aa_eq_ab() {
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let a: Cell<for<'a, 'b> fn(&'a u32, &'b u32)> = make_cell_aa();
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//~^ ERROR mismatched types [E0308]
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//~| ERROR mismatched types [E0308]
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drop(a);
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}
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fn main() { }
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fn main() {}
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22
tests/ui/nll/relate_tys/hr-fn-aau-eq-abu.stderr
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22
tests/ui/nll/relate_tys/hr-fn-aau-eq-abu.stderr
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@ -0,0 +1,22 @@
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error[E0308]: mismatched types
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--> $DIR/hr-fn-aau-eq-abu.rs:18:53
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LL | let a: Cell<for<'a, 'b> fn(&'a u32, &'b u32)> = make_cell_aa();
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| ^^^^^^^^^^^^^^ one type is more general than the other
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= note: expected struct `Cell<for<'a, 'b> fn(&'a _, &'b _)>`
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found struct `Cell<for<'a> fn(&'a _, &'a _)>`
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error[E0308]: mismatched types
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--> $DIR/hr-fn-aau-eq-abu.rs:18:53
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LL | let a: Cell<for<'a, 'b> fn(&'a u32, &'b u32)> = make_cell_aa();
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| ^^^^^^^^^^^^^^ one type is more general than the other
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= note: expected struct `Cell<for<'a, 'b> fn(&'a _, &'b _)>`
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found struct `Cell<for<'a> fn(&'a _, &'a _)>`
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= note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
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error: aborting due to 2 previous errors
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For more information about this error, try `rustc --explain E0308`.
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