Trait method std::os::windows::fs::OpenOptionsExt::security_qos_flags() returns a &mut OpenOptions instead of &mut Self

[Ereski]

https://doc.rust-lang.org/src/std/sys/windows/ext/fs.rs.html#279-281

There's no reason for that method to return a concrete type instead of Self. I am currently writing an OpenOptions wrapper and that method is preventing me from implementing OpenOptionsExt for the wrapper. However, the trait is already stable (even if most likely unimplemented outside libstd) so I'm not sure what's the proper way of changing this?

[alexcrichton]

Thanks for the report @Ereski! Unfortunately though it's very much not the intention of these extension traits to be implemented for foreign types. We added the extension traits to libstd with the intent to eventually add more methods over time as they came up, but we then forgot to add protections to make sure they weren't implemented externally! (our mistake)

In the meantime though I'd recommend either defining inherent methods and/or defining your own extension trait.

[Ereski]

@alexcrichton I see. However in this case (and a few others), the fact that they can't be implemented by external types means wrapper types can't act as drop-in replacements for libstd types in all cases, which is my intent.

Just to clarify, all extensions traits (TypeExt for some type?) are considered unstable to implement and stable to use?

[alexcrichton]

@Ereski yeah at this time the *Ext traits are intended to be internal implementation details of libstd (purely intended as a trait for one particular type).

[retep998]

I believe the current goal is to replace the extension traits with inherent methods directly on the types, but with the portability lint so you're still aware you're using platform specific methods.