Bug: Update readme.md warning about "const fn" issues until rust 1.61 is released.

[PapaTBR]

Which crate is this about?

windows, windows-sys

Crate version

0.34

Summary

Since the current release of windows-rs breaks the under the current stable release of rustc, shouldn't README.md have a big note at the top explaining the situation and the best resolution? Would save everyone the hassle of reporting the "bug" again and again, and help us newbies understand what's going on.

Thanks,
Tom

Toolchain version/configuration

No response

Reproducible example

No response

Crate manifest

No response

Expected behavior

No response

Actual behavior

No response

Additional comments

No response

[riverar]

Hey @PapaTBR, what error are you running into? Where are these duplicate issues you're referring to?

[ryancerium]

I'm guessing a duplicate of #1609, which will have a better error message in 0.35.0. Probably just needs a rustup update to rustc >= 1.59.0 to fix it. It really surprised me.

[riverar]

@PapaTBR Can you provide rustup show output?

[PapaTBR]

Hi guys, thanks for the patience to a rust newbie. :)

Yes, I'm running rustc 1.59, but the stable release, not a nightly (yet.) And the current stable of windows-rs has several known and closed issues about the "const fn" declarations, including the pinned issue #1523.

Thus I think the readme should temporarily reflect the current issue until rustc 1.61 is released. Sure would have saved me several hours trying to figure out what was going on.

When I build the samples I get 1,149 errors:
O:\rust-src\windows-rs-master\crates\samples\xaml_app>cargo build
Compiling windows v0.34.0
error[E0658]: trait bounds other than Sized on const fn parameters are unstable
--> C:\Users\Tom.cargo\registry\src\github.com-1ecc6299db9ec823\windows-0.34.0\src\core\activation_factory.rs:47:22
|
47 | pub const fn new<Identity: ::windows::core::IUnknownImpl, Impl: IActivationFactory_Impl, const OFFSET: isize>() -> IActivationFactory...
| ^^^^^^^^
|
= note: see issue #57563 rust-lang/rust#57563 for more information

error[E0658]: trait bounds other than Sized on const fn parameters are unstable
--> C:\Users\Tom.cargo\registry\src\github.com-1ecc6299db9ec823\windows-0.34.0\src\core\activation_factory.rs:47:63
|
47 | pub const fn new<Identity: ::windows::core::IUnknownImpl, Impl: IActivationFactory_Impl, const OFFSET: isize>() -> IActivationFactory...
| ^^^^
|
= note: see issue #57563 rust-lang/rust#57563 for more information

error[E0658]: function pointer casts are not allowed in constant functions
--> C:\Users\Tom.cargo\registry\src\github.com-1ecc6299db9ec823\windows-0.34.0\src\core\activation_factory.rs:61:31
|
61 | ActivateInstance: ActivateInstance::<Identity, Impl, OFFSET>,
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
= note: see issue #57563 rust-lang/rust#57563 for more information

error[E0658]: trait bounds other than Sized on const fn parameters are unstable

[kennykerr]

Even though it is closed, #1523 is pinned for this purpose.

[kennykerr]

Note that this only impacts the implement and interface features. The vast majority of the windows crate (and all of the windows-sys crate) continues to work on the stable Rust compiler. When you use the implement or interface features, the error message clearly identifies the need for "unstable" and thus the nightly Rust compiler. I can appreciate that this might all be a little confusing if you're new to Rust. 😉

Feel free to reach out with more questions. Closing as duplicate of #1523.