rustdoc:ICE with field that has a conditional Send impl. #60726
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rodrimati1992
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Can you provide a small example (maybe on the playground) that will crash reproducibly? |
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@rodrimati1992: I can't reproduce this crash by running either |
Centril
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T-rustdoc
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With this code: Output: |
Aaron1011
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Fixes rust-lang#60726 Previous, AutoTraitFinder would only try to project predicates when the predicate type contained an inference variable. When finding auto traits, we only project to try to unify inference variables - we don't otherwise learn any new information about the required bounds. However, this lead to failing to properly generate a negative auto trait impl (indicating that a type never implements a certain auto trait) in the following unusual scenario: In almost all cases, a type has an (implicit) negative impl of an auto trait due some other type having an explicit *negative* impl of that auto trait. For example: struct MyType<T> { field: *const T } has an implicit 'impl<T> !Send for MyType<T>', due to the explicit negative impl (in libcore) 'impl<T: ?Sized> !Send for *const T'. However, as exposed by the 'abi_stable' crate, this isn't always the case. This minimzed example shows how a type can never implement 'Send', due to a projection error: ``` pub struct True; pub struct False; pub trait MyTrait { type Project; } pub struct MyStruct<T> { field: T } impl MyTrait for u8 { type Project = False; } unsafe impl<T> Send for MyStruct<T> where T: MyTrait<Project=True> {} pub struct Wrapper { inner: MyStruct<u8> } ``` In this example, `<u8 as MyTrait>::Project == True' must hold for 'MyStruct<u8>: Send' to hold. However, '<u8 as MyTrait>::Project == False' holds instead To properly account for this unusual case, we need to call 'poly_project_and_unify' on *all* predicates, not just those with inference variables. This ensures that we catch the projection error that occurs above, and don't incorrectly determine that 'Wrapper: Send' holds.
Centril
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May 22, 2019
…r=eddyb Always try to project predicates when finding auto traits in rustdoc Fixes rust-lang#60726 Previous, AutoTraitFinder would only try to project predicates when the predicate type contained an inference variable. When finding auto traits, we only project to try to unify inference variables - we don't otherwise learn any new information about the required bounds. However, this lead to failing to properly generate a negative auto trait impl (indicating that a type never implements a certain auto trait) in the following unusual scenario: In almost all cases, a type has an (implicit) negative impl of an auto trait due some other type having an explicit *negative* impl of that auto trait. For example: struct MyType<T> { field: *const T } has an implicit 'impl<T> !Send for MyType<T>', due to the explicit negative impl (in libcore) 'impl<T: ?Sized> !Send for *const T'. However, as exposed by the 'abi_stable' crate, this isn't always the case. This minimzed example shows how a type can never implement 'Send', due to a projection error: ``` pub struct True; pub struct False; pub trait MyTrait { type Project; } pub struct MyStruct<T> { field: T } impl MyTrait for u8 { type Project = False; } unsafe impl<T> Send for MyStruct<T> where T: MyTrait<Project=True> {} pub struct Wrapper { inner: MyStruct<u8> } ``` In this example, `<u8 as MyTrait>::Project == True' must hold for 'MyStruct<u8>: Send' to hold. However, '<u8 as MyTrait>::Project == False' holds instead To properly account for this unusual case, we need to call 'poly_project_and_unify' on *all* predicates, not just those with inference variables. This ensures that we catch the projection error that occurs above, and don't incorrectly determine that 'Wrapper: Send' holds.
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Edited:
Please look at this comment for a self-contained example that reproduces the ICE.
In the process of finishing the 0.3 release of abi_stable,I got this ICE:
Trying it out again in nightly (rustc 1.36.0-nightly (d595b11 2019-05-10) running on i686-unknown-linux-gnu) ,I got:
For the abi_stable::std_types::map::IntoIter type,with this type definition:
It compiles if I add a
PhantomData<Rc<()>>field to IntoIter.Context
The Send impl of DynTrait:
Definition of InterfaceBound
Definition of InterfaceType
The
InterfaceTypeimpl ofValIterInterface:The
impl_InterfaceTypemacro just sets the unmentioned associated types toFalse.The text was updated successfully, but these errors were encountered: