nix doesn't compile with bitflags-1.3.1 on rustc-1.45

[soenkehahn]

bitflags version 1.3.1 was recently released. nix specifies a dependency on bitflags with version constraint "1.1". Without a previously working Cargo.lock file cargo is now free to choose bitflags version 1.3.1 to satisfy nix's dependency. However, with that bitflags version, nix doesn't compile on rustc version 1.45. Here is one of the many errors I get:

error[E0658]: `if` is not allowed in a `const fn`
  --> src/fcntl.rs:28:1
   |
28 | / libc_bitflags! {
29 | |     pub struct AtFlags: c_int {
30 | |         AT_REMOVEDIR;
31 | |         AT_SYMLINK_FOLLOW;
...  |
39 | |     }
40 | | }
   | |_^
   |
   = note: see issue #49146 <https://github.com/rust-lang/rust/issues/49146> for more information
   = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)

Since nix claims to build on rustc-1.41 and upwards, I think this is a bug/misconfiguration.

[soenkehahn]

Here's a related issue on the bitflags repo: bitflags/bitflags#255

[asomers]

Thanks for reporting this. I'll try to fix it and publish a new release soon.

[asomers]

Ok, I released v0.20.1, v0.21.1, and v0.22.1 to fix the issue. I'm not planning to make new releases for older branches, because we switched CI providers beginning with v0.20.0. To those of you still using Nix 0.19.1 or older, upgrade! Either upgrade Nix, or rustc.

[lopopolo]

@asomers when will this restricted dependency version constraint be relaxed? nix has now made the decision for me that I can't update to the newest version of bitflags, despite my project always building with the latest version of rustc.

I believe an acceptable workaround for folks not having a Cargo.lock is to generate one with cargo +nightly -Z minimal-versions generate-lockfile.