in flake mkShell default RUSTFLAGS to an empty string if unset

[plul]

This allows activation of the devshell on systems that don't have a system wide Rust installation.

[the-mikedavis]

What error does this fix? I run nixos without a global Rust installation and no RUSTFLAGS var set and the dev shell works for me without issue

[pascalkuthe]

Yeah rust installations don't even set RUSTFLAGS. An empty environment variable just expands to an empty string so it should work as is

[plul]

Maybe it's a direnv thing, but

❯ direnv reload
direnv: loading ~/repos/github.com/helix-editor/helix/.envrc
direnv: using flake
do you want to allow configuration setting 'extra-substituters' to be set to 'https://helix.cachix.org' (y/N)?
do you want to permanently mark this value as untrusted (y/N)?
warning: ignoring untrusted flake configuration setting 'extra-substituters'.
Pass '--accept-flake-config' to trust it
do you want to allow configuration setting 'extra-trusted-public-keys' to be set to 'helix.cachix.org-1:ejp9KQpR1FBI2onstMQ34yogDm4OgU2ru6lIwPvuCVs=' (y/N)?
do you want to permanently mark this value as untrusted (y/N)?
warning: ignoring untrusted flake configuration setting 'extra-trusted-public-keys'.
Pass '--accept-flake-config' to trust it
direnv: nix-direnv: renewed cache
/home/<me>/.config/direnv/lib/hm-nix-direnv.sh:2475: RUSTFLAGS: unbound variable
direnv: error exit status 127

whereas with export RUSTFLAGS="" ahead of time it works.

[plul]

Yeah nix develop works so looks like a direnv thing. Anyway this fixes it (for me)

[the-mikedavis]

I'm also using direnv but I don't see that error

[plul]

hm weird. Might be messed up on my end somehow then

❯ direnv --version
2.34.0

[plul]

Figured out what causes the error. I have in ~/.config/direnv/direnv.toml:

[global]
strict_env = true

and it is this strict_env = true that causes the error.
From the docs:

If set to true, the .envrc will be loaded with set -euo pipefail. This option will be the default in the future.

[the-mikedavis]

I'm a little skeptical that set -u will ever become the default in direnv because of how much I suspect it would break (of user scripts). Explicitly defaulting the variable seems fine to me though. I just have a small change in mind

[the-mikedavis]

The else branch here will also need the explicit defaulting. Instead we can change the line below for exporting the custom rust flags to

export RUSTFLAGS="''${RUSTFLAGS:-""} ${rustFlagsEnv}"

and remove the $RUSTFLAGS from this variable altogether

[plul]

That's a cleaner approach indeed. Updated.