How can I use nixpkgs.stdenvAdapters.useMoldLinker with craneLib.devShell?

[muni-corn]

I recently stumbled upon crane here and I am trying to wrap my head around how to create a development environment that can use mold. nixpkgs makes this easy with stdenvAdapters. This is my current setup:

devShells.default =
  pkgs.mkShell.override {
    stdenv = pkgs.stdenvAdapters.useMoldLinker pkgs.stdenv;
  } {
    packages =
      nativeBuildInputs
      ++ buildInputs
      ++ (with pkgs; [cargo-watch cargo-outdated]);
    LIBCLANG_PATH = "${pkgs.libclang.lib}/lib";
    LD_LIBRARY_PATH = pkgs.lib.makeLibraryPath buildInputs;
    # other env variables ...
  };

(full flake here, currently using naersk)

but I can't simply replace pkgs.mkShell with craneLib.devShell because stdenv cannot be overridden in the same manner with crane.

What's the best way to go about a similar setup with crane? The goal is to have a development shell that compiles with rustc-codelift (done, easy with fenix) and uses mold for linking to speed up compile time with my Leptos project.

Lots of thanks in advance~!

[ipetkov]

Hi @muni-corn! Two insights which might be helpful here:

1. craneLib.devShell is basically a shortcut for including rustc/cargo/clippy/rustfmt from the toolchain declaration but it isn't strictly required; you can always use pkgs.mkShell directly (and pull in the toolchain override [if any] in there)
2. craneLib.devShell takes a mkShell input, so in theory you could override it like so:

devShells.default = (craneLib.devShell.override {
  mkShell = pkgs.mkShell.override {
    stdenv = pkgs.stdenvAdapters.useMoldLinker pkgs.stdenv;
  };
}) {
  packages = [ /* ... */ ];
};

[muni-corn]

awesome! thank you so much! I'll give this a shot once I have free time again 😁

[ipetkov]

I've also added a note about this in the API docs so hopefully the next person who comes a long won't need to ask again 😄

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