buildDotnetModule: add passthru.fetch-deps

doc/languages-frameworks/dotnet.section.md

@@ -72,7 +72,7 @@ The `dotnetCorePackages.sdk` contains both a runtime and the full sdk of a given
 To package Dotnet applications, you can use `buildDotnetModule`. This has similar arguments to `stdenv.mkDerivation`, with the following additions:
 
 * `projectFile` has to be used for specifying the dotnet project file relative to the source root. These usually have `.sln` or `.csproj` file extensions. This can be an array of multiple projects as well.
-* `nugetDeps` has to be used to specify the NuGet dependency file. Unfortunately, these cannot be deterministically fetched without a lockfile. This file should be generated using `nuget-to-nix` tool, which is available in nixpkgs.
+* `nugetDeps` has to be used to specify the NuGet dependency file. Unfortunately, these cannot be deterministically fetched without a lockfile. A script to fetch these is available as `passthru.fetch-deps`. This file can also be generated manually using `nuget-to-nix` tool, which is available in nixpkgs.
 * `packNupkg` is used to pack project as a `nupkg`, and installs it to `$out/share`. If set to `true`, the derivation can be used as a dependency for another dotnet project by adding it to `projectReferences`.
 * `projectReferences` can be used to resolve `ProjectReference` project items. Referenced projects can be packed with `buildDotnetModule` by setting the `packNupkg = true` attribute and passing a list of derivations to `projectReferences`. Since we are sharing referenced projects as NuGets they must be added to csproj/fsproj files as `PackageReference` as well.
  For example, your project has a local dependency:
@@ -99,6 +99,8 @@ To package Dotnet applications, you can use `buildDotnetModule`. This has simila
 * `dotnetPackFlags` can be used to pass flags to `dotnet pack`. Used only if `packNupkg` is set to `true`.
 * `dotnetFlags` can be used to pass flags to all of the above phases.
 
+When packaging a new application, you need to fetch it's dependencies. You can set `nugetDeps` to an empty string to make the derivation temporarily evaluate, and then run `nix-build -A package.passthru.fetch-deps` to generate it's dependency fetching script. After running the script, you should have the location of the generated lockfile printed to the console. This can be copied to a stable directory. Note that if either `projectFile` or `nugetDeps` are unset, this script cannot be generated!
+
 Here is an example `default.nix`, using some of the previously discussed arguments:
 ```nix
 { lib, buildDotnetModule, dotnetCorePackages, ffmpeg }:
@@ -112,7 +114,8 @@ in buildDotnetModule rec {
   src = ./.;
 
   projectFile = "src/project.sln";
-  nugetDeps = ./deps.nix; # File generated with `nuget-to-nix path/to/src > deps.nix`.
+  nugetDeps = ./deps.nix; # File generated with `nix-build -A package.passthru.fetch-deps`.
+
   projectReferences = [ referencedProject ]; # `referencedProject` must contain `nupkg` in the folder structure.
 
   dotnet-sdk = dotnetCorePackages.sdk_3_1;

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

@@ -1,4 +1,4 @@
-{ lib, stdenvNoCC, linkFarmFromDrvs, makeWrapper, fetchurl, xml2, dotnetCorePackages, dotnetPackages, cacert }:
+{ lib, stdenvNoCC, linkFarmFromDrvs, nuget-to-nix, writeScript, makeWrapper, fetchurl, xml2, dotnetCorePackages, dotnetPackages, cacert }:
 
 { name ? "${args.pname}-${args.version}"
 , enableParallelBuilding ? true
@@ -28,7 +28,7 @@
 # The packages project file, which contains instructions on how to compile it. This can be an array of multiple project files as well.
 , projectFile ? null
 # The NuGet dependency file. This locks all NuGet dependency versions, as otherwise they cannot be deterministically fetched.
-# This can be generated using the `nuget-to-nix` tool.
+# This can be generated by running the `passthru.fetch-deps` script.
 , nugetDeps ? null
 # A list of derivations containing nupkg packages for local project references.
 # Referenced derivations can be built with `buildDotnetModule` with `packNupkg=true` flag.
@@ -63,7 +63,7 @@ assert projectFile == null -> throw "Defining the `projectFile` attribute is req
 
 # TODO: Automatically generate a dependency file when a lockfile is present.
 # This file is unfortunately almost never present, as Microsoft recommands not to push this in upstream repositories.
-assert nugetDeps == null -> throw "Defining the `nugetDeps` attribute is required, as to lock the NuGet dependencies. This file can be generated using the `nuget-to-nix` tool.";
+assert nugetDeps == null -> 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.";
 
 let
   _nugetDeps = linkFarmFromDrvs "${name}-nuget-deps" (import nugetDeps {
@@ -113,6 +113,41 @@ let
     DOTNET_NOLOGO = true; # This disables the welcome message.
     DOTNET_CLI_TELEMETRY_OPTOUT = true;
 
+    passthru.fetch-deps = args.passthru.fetch-deps or writeScript "fetch-${args.pname}-deps" ''
+      set -euo pipefail
+      cd "$(dirname "''${BASH_SOURCE[0]}")"
+
+      export HOME=$(mktemp -d)
+      deps_file="/tmp/${args.pname}-deps.nix"
+
+      store_src="${package.src}"
+      src="$(mktemp -d /tmp/${args.pname}.XXX)"
+      cp -rT "$store_src" "$src"
+      chmod -R +w "$src"
+
+      trap "rm -rf $src $HOME" EXIT
+      pushd "$src"
+
+      export DOTNET_NOLOGO=1
+      export DOTNET_CLI_TELEMETRY_OPTOUT=1
+
+      mkdir -p "$HOME/nuget_pkgs"
+
+      for project in "${lib.concatStringsSep "\" \"" (lib.toList projectFile)}"; do
+        ${dotnet-sdk}/bin/dotnet restore "$project" \
+          ${lib.optionalString (!enableParallelBuilding) "--disable-parallel"} \
+          -p:ContinuousIntegrationBuild=true \
+          -p:Deterministic=true \
+          --packages "$HOME/nuget_pkgs" \
+          "''${dotnetRestoreFlags[@]}" \
+          "''${dotnetFlags[@]}"
+      done
+
+      echo "Writing lockfile..."
+      ${nuget-to-nix}/bin/nuget-to-nix "$HOME/nuget_pkgs" > "$deps_file"
+      echo "Succesfully wrote lockfile to: $deps_file"
+    '';
+
     configurePhase = args.configurePhase or ''
       runHook preConfigure