buildDotnetModule: allow lockFile path to be set in nugetDeps

This allows fetch-deps to find the lock-file for roslyn.

pkgs/build-support/dotnet/build-dotnet-module/default.nix

···
     if (nugetDeps != null) then
       if lib.isDerivation nugetDeps
       then nugetDeps
-      else mkNugetDeps { inherit name; nugetDeps = import nugetDeps; }
+      else mkNugetDeps {
+        inherit name;
+        nugetDeps = import nugetDeps;
+        sourceFile = nugetDeps;
+      }
     else throw "Defining the `nugetDeps` attribute is required, as to lock the NuGet dependencies. This file can be generated by running the `passthru.fetch-deps` script.";
 
   # contains the actual package dependencies
···
     name = "${name}-nuget-source";
     paths = [ dependenciesSource sdkSource ];
   };
+
+  nugetDepsFile = _nugetDeps.sourceFile;
 in
 stdenvNoCC.mkDerivation (args // {
   nativeBuildInputs = args.nativeBuildInputs or [ ] ++ [
···
           # Note that toString is necessary here as it results in the path at
           # eval time (i.e. to the file in your local Nixpkgs checkout) rather
           # than the Nix store path of the path after it's been imported.
-          if lib.isPath nugetDeps && !lib.hasPrefix "${builtins.storeDir}/" (toString nugetDeps)
-          then toString nugetDeps
+          if lib.isPath nugetDepsFile && !lib.hasPrefix "${builtins.storeDir}/" (toString nugetDepsFile)
+          then toString nugetDepsFile
           else ''$(mktemp -t "${pname}-deps-XXXXXX.nix")'';
       in
       writeShellScript "fetch-${pname}-deps" ''

pkgs/build-support/dotnet/make-nuget-deps/default.nix

···
 { linkFarmFromDrvs, fetchurl }:
-{ name, nugetDeps }:
+{ name, nugetDeps, sourceFile ? null }:
 linkFarmFromDrvs "${name}-nuget-deps" (nugetDeps {
   fetchNuGet = { pname, version, sha256
     , url ? "https://www.nuget.org/api/v2/package/${pname}/${version}" }:
···
       name = "${pname}.${version}.nupkg";
       inherit url sha256;
     };
-})
+}) // {
+  inherit sourceFile;
+}

pkgs/development/compilers/roslyn/default.nix

···
 , buildDotnetModule
 , dotnetCorePackages
 , unzip
+, mkNugetDeps
 }:
 
 buildDotnetModule rec {
···
 
   projectFile = [ "src/NuGet/Microsoft.Net.Compilers.Toolset/Microsoft.Net.Compilers.Toolset.Package.csproj" ];
 
-  nugetDeps = ./extended-deps.nix;
+  nugetDeps = mkNugetDeps {
+    name = "${pname}-deps";
+    nugetDeps = import ./extended-deps.nix;
+    sourceFile = ./deps.nix;
+  };
 
   dontDotnetFixup = true;