Well, I did move it to nixpkgs now
Got it all working, but now I’m getting this error:

ab-street> error: failed to parse manifest at `/build/source/abstio/Cargo.toml`
ab-street> Caused by:
ab-street>   feature `edition2021` is required
ab-street>   consider adding `cargo-features = ["edition2021"]` to the manifest
ab-street> Traceback (most recent call last):
ab-street>   File "/nix/store/bxlx1dy64ywk6spy265jm53qz3a45yc9-cargo-vendor-normalise/bin/.cargo-vendor-normalise-wrapped", line 42, in <module>
ab-street>     main()
ab-street>   File "/nix/store/bxlx1dy64ywk6spy265jm53qz3a45yc9-cargo-vendor-normalise/bin/.cargo-vendor-normalise-wrapped", line 17, in main
ab-street>     assert list(data.keys()) == ["source"]
ab-street> AssertionError

[12:37:15] jon@nixos ~/projects/nixpkgs (staging-next)
$ nix-build -A rustc
/nix/store/449lmdsx8dv2q5fn4xbkxk51d4cg2zih-rustc-1.56.1

In reply to @jonringer:matrix.org
if you're hacking within nixpkgs. git rebase --onto=origin/staging-next HEAD~1