the packages contain code that will become an error in a future release of Rust: "conflicting implementation for (dyn Send + Sync + 'static)"

[phansel]

Reporting some issues seen while building an application under stable rust 1.67.0. Haven't seen this one before.

$ cargo report future-incompatibilities --id 2 --package traitobject@0.1.0

The following warnings were discovered during the build. These warnings are an
indication that the packages contain code that will become an error in a
future release of Rust. These warnings typically cover changes to close
soundness problems, unintended or undocumented behavior, or critical problems
that cannot be fixed in a backwards-compatible fashion, and are not expected
to be in wide use.

Each warning should contain a link for more information on what the warning
means and how to resolve it.


To solve this problem, you can try the following approaches:


- If the issue is not solved by updating the dependencies, a fix has to be
implemented by those dependencies. You can help with that by notifying the
maintainers of this problem (e.g. by creating a bug report) or by proposing a
fix to the maintainers (e.g. by creating a pull request):

  - traitobject@0.1.0
  - Repository: https://github.com/reem/rust-traitobject.git
  - Detailed warning command: `cargo report future-incompatibilities --id 2 --package traitobject@0.1.0`

- If waiting for an upstream fix is not an option, you can use the `[patch]`
section in `Cargo.toml` to use your own version of the dependency. For more
information, see:
https://doc.rust-lang.org/cargo/reference/overriding-dependencies.html#the-patch-section
        
The package `traitobject v0.1.0` currently triggers the following future incompatibility lints:
> warning: conflicting implementations of trait `Trait` for type `(dyn Send + Sync + 'static)`: (E0119)
>   --> /home/user/.cargo/registry/src/git.luolix.top-1ecc6299db9ec823/traitobject-0.1.0/src/impls.rs:72:1
>    |
> 71 | unsafe impl Trait for ::std::marker::Send + Sync { }
>    | ------------------------------------------------ first implementation here
> 72 | unsafe impl Trait for ::std::marker::Send + Send + Sync { }
>    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `(dyn Send + Sync + 'static)`
>    |
>    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
>    = note: for more information, see issue #56484 <https://github.com/rust-lang/rust/issues/56484>
>    = note: `#[allow(order_dependent_trait_objects)]` on by default
> 
> warning: conflicting implementations of trait `Trait` for type `(dyn Send + Sync + 'static)`: (E0119)
>   --> /home/user/.cargo/registry/src/git.luolix.top-1ecc6299db9ec823/traitobject-0.1.0/src/impls.rs:73:1
>    |
> 72 | unsafe impl Trait for ::std::marker::Send + Send + Sync { }
>    | ------------------------------------------------------- first implementation here
> 73 | unsafe impl Trait for ::std::marker::Sync + Send { }
>    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `(dyn Send + Sync + 'static)`
>    |
>    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
>    = note: for more information, see issue #56484 <https://github.com/rust-lang/rust/issues/56484>
>    = note: `#[allow(order_dependent_trait_objects)]` on by default
> 
> warning: conflicting implementations of trait `Trait` for type `(dyn Send + Sync + 'static)`: (E0119)
>   --> /home/user/.cargo/registry/src/git.luolix.top-1ecc6299db9ec823/traitobject-0.1.0/src/impls.rs:75:1
>    |
> 73 | unsafe impl Trait for ::std::marker::Sync + Send { }
>    | ------------------------------------------------ first implementation here
> 74 | unsafe impl Trait for ::std::marker::Sync + Sync { }
> 75 | unsafe impl Trait for ::std::marker::Sync + Send + Sync { }
>    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `(dyn Send + Sync + 'static)`
>    |
>    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
>    = note: for more information, see issue #56484 <https://github.com/rust-lang/rust/issues/56484>
>    = note: `#[allow(order_dependent_trait_objects)]` on by default
> 

[Harveyhase68]

Any updates on this?

[velechva]

Hi @reem I believe you can fix this by replacing the reundant trait impl's with simply:

unsafe impl Trait for ::std::marker::Send { }
unsafe impl Trait for ::std::marker::Sync { }

Could you look into this?