Dotnet

Local Development Workflow

For local development, it's recommended to use nix-shell to create a dotnet environment:

# shell.nix
with import <nixpkgs> {};

mkShell {
  name = "dotnet-env";
  packages = [
    dotnet-sdk_3
  ];
}

Using many sdks in a workflow

It's very likely that more than one sdk will be needed on a given project. Dotnet provides several different frameworks (E.g dotnetcore, aspnetcore, etc.) as well as many versions for a given framework. Normally, dotnet is able to fetch a framework and install it relative to the executable. However, this would mean writing to the nix store in nixpkgs, which is read-only. To support the many-sdk use case, one can compose an environment using dotnetCorePackages.combinePackages:

with import <nixpkgs> {};

mkShell {
  name = "dotnet-env";
  packages = [
    (with dotnetCorePackages; combinePackages [
      sdk_3_1
      sdk_5_0
    ])
  ];
}

This will produce a dotnet installation that has the dotnet 3.1, 3.0, and 2.1 sdk. The first sdk listed will have it's cli utility present in the resulting environment. Example info output:

$ dotnet --info
.NET Core SDK (reflecting any global.json):
 Version:   3.1.101
 Commit:    b377529961

...

.NET Core SDKs installed:
  2.1.803 [/nix/store/iiv98i2jdi226dgh4jzkkj2ww7f8jgpd-dotnet-core-combined/sdk]
  3.0.102 [/nix/store/iiv98i2jdi226dgh4jzkkj2ww7f8jgpd-dotnet-core-combined/sdk]
  3.1.101 [/nix/store/iiv98i2jdi226dgh4jzkkj2ww7f8jgpd-dotnet-core-combined/sdk]

.NET Core runtimes installed:
  Microsoft.AspNetCore.All 2.1.15 [/nix/store/iiv98i2jdi226dgh4jzkkj2ww7f8jgpd-dotnet-core-combined/shared/Microsoft.AspNetCore.All]
  Microsoft.AspNetCore.App 2.1.15 [/nix/store/iiv98i2jdi226dgh4jzkkj2ww7f8jgpd-dotnet-core-combined/shared/Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 3.0.2 [/nix/store/iiv98i2jdi226dgh4jzkkj2ww7f8jgpd-dotnet-core-combined/shared/Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 3.1.1 [/nix/store/iiv98i2jdi226dgh4jzkkj2ww7f8jgpd-dotnet-core-combined/shared/Microsoft.AspNetCore.App]
  Microsoft.NETCore.App 2.1.15 [/nix/store/iiv98i2jdi226dgh4jzkkj2ww7f8jgpd-dotnet-core-combined/shared/Microsoft.NETCore.App]
  Microsoft.NETCore.App 3.0.2 [/nix/store/iiv98i2jdi226dgh4jzkkj2ww7f8jgpd-dotnet-core-combined/shared/Microsoft.NETCore.App]
  Microsoft.NETCore.App 3.1.1 [/nix/store/iiv98i2jdi226dgh4jzkkj2ww7f8jgpd-dotnet-core-combined/shared/Microsoft.NETCore.App]

dotnet-sdk vs dotnetCorePackages.sdk

The dotnetCorePackages.sdk_X_Y is preferred over the old dotnet-sdk as both major and minor version are very important for a dotnet environment. If a given minor version isn't present (or was changed), then this will likely break your ability to build a project.

dotnetCorePackages.sdk vs dotnetCorePackages.runtime vs dotnetCorePackages.aspnetcore

The dotnetCorePackages.sdk contains both a runtime and the full sdk of a given version. The runtime and aspnetcore packages are meant to serve as minimal runtimes to deploy alongside already built applications.

Packaging a Dotnet Application

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.
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.
executables is used to specify which executables get wrapped to $out/bin, relative to $out/lib/$pname. If this is unset, all executables generated will get installed. If you do not want to install any, set this to [].
runtimeDeps is used to wrap libraries into LD_LIBRARY_PATH. This is how dotnet usually handles runtime dependencies.
buildType is used to change the type of build. Possible values are Release, Debug, etc. By default, this is set to Release.
dotnet-sdk is useful in cases where you need to change what dotnet SDK is being used.
dotnet-runtime is useful in cases where you need to change what dotnet runtime is being used. This can be either a regular dotnet runtime, or an aspnetcore.
dotnet-test-sdk is useful in cases where unit tests expect a different dotnet SDK. By default, this is set to the dotnet-sdk attribute.
testProjectFile is useful in cases where the regular project file does not contain the unit tests. By default, this is set to the projectFile attribute.
disabledTests is used to disable running specific unit tests. This gets passed as: dotnet test --filter "FullyQualifiedName!={}", to ensure compatibility with all unit test frameworks.
dotnetRestoreFlags can be used to pass flags to dotnet restore.
dotnetBuildFlags can be used to pass flags to dotnet build.
dotnetTestFlags can be used to pass flags to dotnet test.
dotnetInstallFlags can be used to pass flags to dotnet install.
dotnetFlags can be used to pass flags to all of the above phases.

Here is an example default.nix, using some of the previously discussed arguments:

{ lib, buildDotnetModule, dotnetCorePackages, ffmpeg }:

buildDotnetModule rec {
  pname = "someDotnetApplication";
  version = "0.1";

  src = ./.;

  projectFile = "src/project.sln";
  nugetDeps = ./deps.nix; # File generated with `nuget-to-nix path/to/src > deps.nix`.

  dotnet-sdk = dotnetCorePackages.sdk_3_1;
  dotnet-runtime = dotnetCorePackages.net_5_0;
  dotnetFlags = [ "--runtime linux-x64" ];

  executables = [ "foo" ]; # This wraps "$out/lib/$pname/foo" to `$out/bin/foo`.
  executables = []; # Don't install any executables.

  runtimeDeps = [ ffmpeg ]; # This will wrap ffmpeg's library path into `LD_LIBRARY_PATH`.
}

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