Can cargo2nix run -Zbuild-std cross-compiling for embedded targets?

[wrsturgeon]

Title. This tool blew my mind, by the way—this is just an edge case that I'm wondering if you support. If not, I'll just use a less Nix-y way.

[wrsturgeon]

Apologies, I should be more specific:

I'm not entirely clear where to introduce this option.

• I already have .cargo/config and rust-toolchain specifying -Zbuild-std and a bunch of other options (which works without Nix), but cargo2nix doesn't recognize them—I'm assuming this is on purpose? Still, nightly is no problem (thanks to makePackageSet), but I can't find the best way to introduce -Zbuild-std.
• The Rust target is thumb-v6m-none-eabi (an Arduino MKR WIFI, clearly no OS), so this can't work with the crossSystem argument as in your cross-compilation example (tried, unrecognized).
• There doesn't seem to be another way in arguments to makePackageSet. I've used nightly already and set the target, but a few crates fail with a missing panic handler, a symptom of not having std available, so it seems that std does not build by default when cross-compiling (sensible), but I can't use the cargo2nix method of cross-compilation, either.
• I'm not sure it's the best way to override the environment variables, and I'll admit I'm not sure how to do this and haven't found an example. My intuition is that this is not the safest way to do it, but that's why I ask for help.

If this is too hand-wave-y / a waste of your time, let me know, but I'd appreciate any pointers!

[heph2]

Hi @wrsturgeon i'm currently trying to use cargo2nix for build an embedded project (raspberry pico) and i'm also having some issues..
Do you mind share your flake.nix?

[psionic-k]

cargo2nix is an expression-generator style solution. The generator, cargo2nix, doesn't deal with any -Z flags.

Later on, the overlay we provide does consume flags. My plan is to handle this soon by adding the most generic flags options first and then adding the more specific ones to line up the user experience to match other Rust nix tooling.