Move to Rust edition 2021 and version 1.56

[kennykerr]

Now that the major crate dependencies like syn and tokio have moved to 1.56 or later, windows-rs can finally make the move to the 2021 edition of Rust and MSRV for windows and windows-sys will be 1.56 from here on.

[kennykerr]

Looks like this is failing due to a change in 2021: https://doc.rust-lang.org/stable/edition-guide/rust-2021/reserving-syntax.html

[TheBlueMatt]

tokio still supports 1.49 still on their LTS release of 1.25, which was broken by this.

[Thomasdezeeuw]

@TheBlueMatt I don't think that's true, Mio only depends on v0.48, see https://github.com/tokio-rs/mio/blob/8dd37c5e14bf7031365321c5aad5dc85788b9a09/Cargo.toml#L52, Cargo isn't allowed to use v0.49 or v0.50 because of that.

[TheBlueMatt]

Not sure what you mean by 0.49 or 0.50 (I don't see a windows-sys or windows-targets version for either of those, but windows-sys 0.48 depends on windows-targets 0.48... which got switched to windows-targets 0.48.3, which is what ultimately broke here.

[TheBlueMatt]

See specifically the dependency tree posted at tokio-rs/tokio#5934 (comment) which shows mio depending on 0.48 and windows-targets v0.48.3 (which broke the previous M"S"RV of windows-targets).

[TheBlueMatt]

The following script run in an empty directory illustrates the change in M"S"RV in the windows-targets crate(s) reached via mio in tokio 1.25.1, which is still supported and has a non-windows MSRV of 1.49:

#/bin/sh
rustup default 1.49
cargo init .
echo 'tokio = { version = "=1.25.1", features = ["net"] }' >> Cargo.toml
cargo tree --target x86_64-pc-windows-msvc # This fails
cargo update -p windows-targets:0.48.3 --precise "0.48.1" --verbose
cargo update -p windows_aarch64_gnullvm:0.48.3 --precise "0.48.0" --verbose
cargo update -p windows_x86_64_gnullvm:0.48.3 --precise "0.48.0" --verbose
cargo update -p windows_x86_64_gnu:0.48.3 --precise "0.48.0" --verbose
cargo update -p windows_i686_gnu:0.48.3 --precise "0.48.0" --verbose
cargo update -p windows_aarch64_msvc:0.48.3 --precise "0.48.0" --verbose
cargo update -p windows_x86_64_msvc:0.48.3 --precise "0.48.0" --verbose
cargo update -p windows_i686_msvc:0.48.3 --precise "0.48.0" --verbose
cargo tree --target x86_64-pc-windows-msvc # This now passes

[kennykerr]

Hopefully #2613 will help.

[TheBlueMatt]

Thanks! That would certainly address the issue I'm hitting. However, more generally, I took your comment at tokio-rs/tokio#5934 (comment) to imply that there is no MSRV (ie version supported, not just the field in the Cargo.toml) which would imply that this issue could happen in the future and its not explicitly supported? Is that true or did I miunderstand your comment (is the MSRV here fixed for a given minor version?). Of course there's no pressure on any project to support anything they don't want to, I just want to know what is supported for our own reference and build systems.

[kennykerr]

That comment was purely about the fact that Rust 1.48 doesn't support the version key.

[TheBlueMatt]

Ah, I definitely very much misunderstood that comment. Could you comment on the MSRV (policy, not keys) of the windows-rs crate family?

[kennykerr]

The 0.48 crates have an MSRV of 1.48 while the newer crates have an MSRV of 1.56.

So this was not intentional. it's just that testing 1.48 is virtually impossible.

[TheBlueMatt]

Ah! Okay, thanks. Much appreciated.