I can't quite figure out how to pass dependencies properly to the dll. Right now I have this:

...
  nupkg = dotnetCorePackages.fetchNupkg {
    inherit url version pname;
    sha256 = "sha256-Cq2t0TkGtmGpMcFrz9m0FJ14F4knfDoGaUFda9dijik=";
  };
in
stdenvNoCC.mkDerivation {
  inherit version pname;
  nativeBuildInputs = [
    makeWrapper
    # dotnetCorePackages.runtime_8_0
    dotnetCorePackages.sdk_8_0
  ];

  buildInputs = [
    dotnetCorePackages.runtime_8_0
    # dotnetCorePackages.sdk_8_0
  ];
  src = nupkg;

  installPhase = ''
    runHook preInstall

    mkdir -p $out/bin

    makeWrapper ${lib.getExe dotnetCorePackages.runtime_8_0-bin} $out/bin/${pname} \
          --add-flags "exec ${nupkg}/share/nuget/packages/${lib.toLower pname}/${version}/lib/net8.0/${pname}.dll"

    runHook postInstall
  '';

But it says:

A fatal error was encountered. The library 'libhostpolicy.so' required to execute the application was not found in '/nix/store/yjszifiind26c7vpvyg4c3m49lgksv0z-somepkg-1.0.98/share/nuget/packages/somepkg/1.0.98/lib/net8.0/'

I tried to shuffle sdk and runtime around, sometimes getting this error:

       > Running phase: configureNuget
       > The command could not be loaded, possibly because:
       >   * You intended to execute a .NET application:
       >       The application 'new' does not exist.
       >   * You intended to execute a .NET SDK command:
       >       No .NET SDKs were found.

But I'm assuming that's because nuget is getting confused depending on what's on the path

Either way this is what I have right now:

{
  lib,
  dotnetCorePackages,
  makeWrapper,
  stdenvNoCC,
}:

let
  url = "${customNugetServer}(Id='${pname}',Version='${version}')/Download";
  dlls = dotnetCorePackages.fetchNupkg {
    inherit url version pname;
    sha256 = "sha256-xEPmYA0wkQrDBl82HDa6khIMltNUV5gdzayt6J1Lwpw=";
  };
in

with dotnetCorePackages;

buildDotnetModule {
  inherit pname version;
  src = webapi-src;

  buildInputs = [
    aspnetcore_9_0
    dlls
  ];

  dotnet-sdk = sdk_9_0;
  dotnet-runtime = runtime_9_0;
}

And it gets me this far:

       > Running phase: configureNuget
       > The template "NuGet Config" was created successfully.
       >
       > Processing post-creation actions...
       >
       >
       > Running phase: updateAutotoolsGnuConfigScriptsPhase
       > Running phase: configurePhase
       > Executing dotnetConfigureHook
       >   Determining projects to restore...
       > /build/myAPI/myApi.csproj : error NU1101: Unable to find package Swashbuckle.AspNetCore. No packages exist with this id in source(s): _nix

That seems like some great piece of tooling.

Sorry, that sounded sarcastic, I meant it seriously 😅 and thanks for your help so far

doing a nix build .\#thing.passthru.fetch-deps && ./result fails with this:

/nix/store/q38z0zig1346h47vyianirr25fi9g42m-fetch-deps.sh: line 10: /nix/store/rxf86xrfxhij48hjqgysi8blj2c9hg88-source/ArcaneLibs.Blazor.Components/deps.nix: Read-only file system

In reply to @emma:rory.gay

doing a nix build .\#thing.passthru.fetch-deps && ./result fails with this:

/nix/store/q38z0zig1346h47vyianirr25fi9g42m-fetch-deps.sh: line 10: /nix/store/rxf86xrfxhij48hjqgysi8blj2c9hg88-source/ArcaneLibs.Blazor.Components/deps.nix: Read-only file system