Here is my script:

#!/usr/bin/env nu
# Generate a flamegraph from a nix flake evaluation
# Usage: script.nu <flake-path>

def main [flake_path: string] {
    print $"Evaluating flake: ($flake_path)"

    # Create temporary directory for profile data
    let tmp_dir = (mktemp -d)
    let profile_path = ($tmp_dir | path join "nix.profile")

    # Run nix eval with profiler output
    nix eval --impure --no-eval-cache $flake_path --option eval-profiler flamegraph --option eval-profile-file $profile_path

    # Generate flamegraph SVG from profile data
    open $profile_path | inferno-flamegraph | save -f flamegraph.svg

    print "Flamegraph saved to flamegraph.svg"
}

Here is my Nushell script:

#!/usr/bin/env nu
# Generate a flamegraph from a nix flake evaluation
# Usage: script.nu <flake-path>

def main [flake_path: string] {
    print $"Evaluating flake: ($flake_path)"

    # Create temporary directory for profile data
    let tmp_dir = (mktemp -d)
    let profile_path = ($tmp_dir | path join "nix.profile")

    # Run nix eval with profiler output
    nix eval --impure --no-eval-cache $flake_path --option eval-profiler flamegraph --option eval-profile-file $profile_path

    # Generate flamegraph SVG from profile data
    open $profile_path | inferno-flamegraph | save -f flamegraph.svg

    print "Flamegraph saved to flamegraph.svg"
}

        checks = nix-config.checks;

error: The option `checks.<function body>' was accessed but has no value defined. Try setting the option.

checks = nix-config.checks;

error: The option `checks.<function body>' was accessed but has no value defined. Try setting the option.

interestingly, something like the following in nix/withOverlays/default.nix works:

final: prev: (prev.lib.composeManyExtensions [
  prev.inputs.nixgl.overlays.default
  prev.inputs.emacs-overlay.overlays.package
  prev.inputs.self.overlays.overrides
  prev.inputs.self.overlays.lix
]) final prev

So computing the module arguments is triggering evaluation of withOverlays... hmm

Does it make sense that this is supported?: (How does Flakelight know whether it is an overlay or a function to setup multiple overlays, like in my example ?)

withOverlays = overlay; 

Shouldn't it only support?:

withOverlays = [overlay, ...];