Git 3.0, Rust and other timelines

[rimrul]

Git 3.0 will most likely require Rust. This comes with a couple of minor challenges for Git for Windows. While there is no fixed release date for Git 3.0 yet, I'd like to discuss how we want to approach these, so we are prepared for Git 3.0.

ARM64

I don't see any challenges for ARM64, we could probably start building WITH_RUST right now.

Windows 8.1 support

We're currently still supporting Windows 8.1. Rust raised the requirements for the regular *-windows-gnu targets to Windows 10 in version 1.76.

Theoretically we could stick to an older (unmaintained) version. Git currently only requires 1.49 or newer. We'd probably have to build our own mingw-w64-rust package (based on Msys2s old PKGBUILD).

We could also switch to the new tier 3 *-win7-windows-gnu targets available since version 1.86. Being tier 3 targets, rust doesn't guarrantee that these even build. We'd also have to build our own mingw-w64-rust package (based on MSYS2s current PKGBUILD).

We could also drop support for Windows 8.1, but I'm not sure how intertwined our 32-bit MinGit timeline until 2029, VS2019s EOL in 2029 and Git Credential Managers Windows 8.1 Support until 2029 are.

32-bit support

There are efforts in MSYS2 to drop the 32-bit *-windows-gnu targets. Our options in that case are pinning an old (i.e. before the dropping) rust version or building our own mingw-w64-rust package.

@dscho @mjcheetham , what are your thoughts?