It looks like rust is too old?!

rust_clap> error[E0658]: arbitrary expressions in key-value attributes are unstable
rust_clap>  --> src/lib.rs:8:10
rust_clap>   |
rust_clap> 8 | #![doc = include_str!("../README.md")]
rust_clap>   |          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
rust_clap>   |
rust_clap>   = note: see issue #78835 <https://github.com/rust-lang/rust/issues/78835> for more information
rust_clap> error[E0658]: use of unstable library feature 'osstring_ascii'
rust_clap>    --> src/parse/matches/matched_arg.rs:130:19
rust_clap>     |
rust_clap> 130 |                 v.eq_ignore_ascii_case(val)
rust_clap>     |                   ^^^^^^^^^^^^^^^^^^^^
rust_clap>     |
rust_clap>     = note: see issue #70516 <https://github.com/rust-lang/rust/issues/70516> for more information

You’ll need the following patch to make Cargo.nix match Cargo.lock before you can try to build pijul.

This change fixes the issue by updating rust to 1.54.0.

Thanks! I just applied your change to main.