How to add overrides to defaultCrateOverrides

[Profpatsch]

The README mentions

If your library with native dependencies is not yet supported, you can create an overlay to add the needed configuration to the defaultCrateOverrides

But it’s not clear to me how that can be done. For example, I can’t find the string defaultCrateOverrides in the generated nix file.

[kolloch]

Note that this is part of the "standard" buildRustCrate support that comes with NixOS. I think it would be very valuable to document this well!

Some rudimentary doc is here: https://git.mayflower.de/NixOS/nixpkgs/blob/master/doc/languages-frameworks/rust.md#compiling-rust-crates-using-nix-instead-of-cargo

I appreciate pull requests for the README.md for crate2nix or the nixos doc itself.

[danieldk]

Could you give a hint of how to do this? Normally buildRustCrate gives a derivation that is overridable, which allows overriding crateOverrides, so that something like the following works:

with import <nixpkgs> {};
((import ./hello.nix).hello {}).override {
  crateOverrides = defaultCrateOverrides // {
    hello = attrs: { buildInputs = [ openssl ]; };
  };
}

However, the file generated by crate2nix uses makeOverrideable again on the derivation (in buildRustCrateWithFeatures), for providing the feature overriding functionality. However, this seems to 'override the override', hiding the buildRustCrate variant?

Something like the above fails with:

error: anonymous function at /home/daniel/.config/nixpkgs/nix-nlp/pkgs/finalfrontier/finalfrontier.nix:2182:8 called with unexpected argument 'crateOverrides', at /home/daniel/git/nixpkgs/lib/customisation.nix:69:12

[danieldk]

Just to confirm, if I apply this diff to the generated Nix file, I can use crateOverrides:

-  buildRustCrateWithFeatures = {packageId, features}:
-    lib.makeOverridable
-      ({features}: buildRustCrateWithFeaturesImpl {inherit packageId features;})
-      { inherit features; };
+  buildRustCrateWithFeatures = buildRustCrateWithFeaturesImpl;

[kolloch]

You could also override the defaultCrateOverrides in pkgs with an overlay. Thanks for the detective work.

I'll add crateOverrides to the overridable parameters since it would be an incompatibility otherwise.