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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
  ];
}

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_6_0
      sdk_7_0
    ])
  ];
}

This will produce a dotnet installation that has the dotnet 6.0 7.0 sdk. The first sdk listed will have it's cli utility present in the resulting environment. Example info output:

$ dotnet --info
.NET SDK:
 Version:   7.0.202
 Commit:    6c74320bc3

Środowisko uruchomieniowe:
 OS Name:     nixos
 OS Version:  23.05
 OS Platform: Linux
 RID:         linux-x64
 Base Path:   /nix/store/n2pm44xq20hz7ybsasgmd7p3yh31gnh4-dotnet-sdk-7.0.202/sdk/7.0.202/

Host:
  Version:      7.0.4
  Architecture: x64
  Commit:       0a396acafe

.NET SDKs installed:
  6.0.407 [/nix/store/3b19303vwrhv0xxz1hg355c7f2hgxxgd-dotnet-core-combined/sdk]
  7.0.202 [/nix/store/3b19303vwrhv0xxz1hg355c7f2hgxxgd-dotnet-core-combined/sdk]

.NET runtimes installed:
  Microsoft.AspNetCore.App 6.0.15 [/nix/store/3b19303vwrhv0xxz1hg355c7f2hgxxgd-dotnet-core-combined/shared/Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 7.0.4 [/nix/store/3b19303vwrhv0xxz1hg355c7f2hgxxgd-dotnet-core-combined/shared/Microsoft.AspNetCore.App]
  Microsoft.NETCore.App 6.0.15 [/nix/store/3b19303vwrhv0xxz1hg355c7f2hgxxgd-dotnet-core-combined/shared/Microsoft.NETCore.App]
  Microsoft.NETCore.App 7.0.4 [/nix/store/3b19303vwrhv0xxz1hg355c7f2hgxxgd-dotnet-core-combined/shared/Microsoft.NETCore.App]

Other architectures found:
  None

Environment variables:
  Not set

global.json file:
  Not found

Learn more:
  https://aka.ms/dotnet/info

Download .NET:
  https://aka.ms/dotnet/download

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 is used for specifying the dotnet project file, relative to the source root. These have .sln (entire solution) or .csproj (single project) file extensions. This can be a list of multiple projects as well. When omitted, will attempt to find and build the solution (.sln). If running into problems, make sure to set it to a file (or a list of files) with the .csproj extension - building applications as entire solutions is not fully supported by the .NET CLI.
nugetDeps takes either a path to a deps.nix file, or a derivation. The deps.nix file can be generated using the script attached to passthru.fetch-deps. If the argument is a derivation, it will be used directly and assume it has the same output as mkNugetDeps. ::: {.note} For more detail about managing the deps.nix file, see Generating and updating NuGet dependencies :::
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:

    <ProjectReference Include="../foo/bar.fsproj" />

To enable discovery through projectReferences you would need to add:

    <ProjectReference Include="../foo/bar.fsproj" />
    <PackageReference Include="bar" Version="*" Condition=" '$(ContinuousIntegrationBuild)'=='true' "/>

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 []. This gets done in the preFixup phase.
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.
selfContainedBuild allows to enable the self-contained build flag. By default, it is set to false and generated applications have a dependency on the selected dotnet runtime. If enabled, the dotnet runtime is bundled into the executable and the built app has no dependency on .NET.
useAppHost will enable creation of a binary executable that runs the .NET application using the specified root. More info in Microsoft docs. Enabled by default.
useDotnetFromEnv will change the binary wrapper so that it uses the .NET from the environment. The runtime specified by dotnet-runtime is given as a fallback in case no .NET is installed in the user's environment. This is most useful for .NET global tools and LSP servers, which often extend the .NET CLI and their runtime should match the users' .NET runtime.
dotnet-sdk is useful in cases where you need to change what dotnet SDK is being used. You can also set this to the result of dotnetSdkPackages.combinePackages, if the project uses multiple SDKs to build.
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.
testProjectFile is useful in cases where the regular project file does not contain the unit tests. It gets restored and build, but not installed. You may need to regenerate your nuget lockfile after setting this. Note that if set, only tests from this project are executed.
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. Used only if doCheck is set to true.
dotnetInstallFlags can be used to pass flags to dotnet install.
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 its dependencies. Create an empty deps.nix, set nugetDeps = ./deps.nix, then run nix-build -A package.fetch-deps to generate a script that will build the lockfile for you.

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

{ lib, buildDotnetModule, dotnetCorePackages, ffmpeg }:

let
  referencedProject = import ../../bar { /* ... */ };
in buildDotnetModule rec {
  pname = "someDotnetApplication";
  version = "0.1";

  src = ./.;

  projectFile = "src/project.sln";
  nugetDeps = ./deps.nix; # see "Generating and updating NuGet dependencies" section for details

  projectReferences = [ referencedProject ]; # `referencedProject` must contain `nupkg` in the folder structure.

  dotnet-sdk = dotnetCorePackages.sdk_6_0;
  dotnet-runtime = dotnetCorePackages.runtime_6_0;

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

  packNupkg = true; # This packs the project as "foo-0.1.nupkg" at `$out/share`.

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

Keep in mind that you can tag the @NixOS/dotnet team for help and code review.

Dotnet global tools

.NET Global tools are a mechanism provided by the dotnet CLI to install .NET binaries from Nuget packages.

They can be installed either as a global tool for the entire system, or as a local tool specific to project.

The local installation is the easiest and works on NixOS in the same way as on other Linux distributions. See dotnet documentation to learn more.

The global installation method should also work most of the time. You have to remember to update the PATH value to the location the tools are installed to (the CLI will inform you about it during installation) and also set the DOTNET_ROOT value, so that the tool can find the .NET SDK package. You can find the path to the SDK by running nix eval --raw nixpkgs#dotnet-sdk (substitute the dotnet-sdk package for another if a different SDK version is needed).

This method is not recommended on NixOS, since it's not declarative and involves installing binaries not made for NixOS, which will not always work.

The third, and preferred way, is packaging the tool into a Nix derivation.

Packaging Dotnet global tools

Dotnet global tools are standard .NET binaries, just made available through a special NuGet package. Therefore, they can be built and packaged like every .NET application, using buildDotnetModule.

If however the source is not available or difficult to build, the buildDotnetGlobalTool helper can be used, which will package the tool straight from its NuGet package.

This helper has the same arguments as buildDotnetModule, with a few differences:

pname and version are required, and will be used to find the NuGet package of the tool
nugetName can be used to override the NuGet package name that will be downloaded, if it's different from pname
nugetSha256 is the hash of the fetched NuGet package. Set this to lib.fakeHash256 for the first build, and it will error out, giving you the proper hash. Also remember to update it during version updates (it will not error out if you just change the version while having a fetched package in /nix/store)
dotnet-runtime is set to dotnet-sdk by default. When changing this, remember that .NET tools fetched from NuGet require an SDK.

Here is an example of packaging pbm, an unfree binary without source available:

{ buildDotnetGlobalTool, lib }:

buildDotnetGlobalTool {
  pname = "pbm";
  version = "1.3.1";

  nugetSha256 = "sha256-ZG2HFyKYhVNVYd2kRlkbAjZJq88OADe3yjxmLuxXDUo=";

  meta = {
    homepage = "https://cmd.petabridge.com/index.html";
    changelog = "https://cmd.petabridge.com/articles/RELEASE_NOTES.html";
    license = lib.licenses.unfree;
    platforms = lib.platforms.linux;
  };
}

Generating and updating NuGet dependencies

When writing a new expression, you can use the generated fetch-deps script to initialise the lockfile. After creating a blank deps.nix and pointing nugetDeps to it, build the script with nix-build -A package.fetch-deps and then run the result. (When the root attr is your package, it's simply nix-build -A fetch-deps.)

There is also a manual method: First, restore the packages to the out directory, ensure you have cloned the upstream repository and you are inside it.

$ dotnet restore --packages out
  Determining projects to restore...
  Restored /home/lychee/Celeste64/Celeste64.csproj (in 1.21 sec).

Next, use nuget-to-nix tool provided in nixpkgs to generate a lockfile to deps.nix from the packages inside the out directory.

$ nuget-to-nix out > deps.nix

Which nuget-to-nix will generate an output similar to below

{ fetchNuGet }: [
  (fetchNuGet { pname = "FosterFramework"; version = "0.1.15-alpha"; sha256 = "0pzsdfbsfx28xfqljcwy100xhbs6wyx0z1d5qxgmv3l60di9xkll"; })
  (fetchNuGet { pname = "Microsoft.AspNetCore.App.Runtime.linux-x64"; version = "8.0.1"; sha256 = "1gjz379y61ag9whi78qxx09bwkwcznkx2mzypgycibxk61g11da1"; })
  (fetchNuGet { pname = "Microsoft.NET.ILLink.Tasks"; version = "8.0.1"; sha256 = "1drbgqdcvbpisjn8mqfgba1pwb6yri80qc4mfvyczqwrcsj5k2ja"; })
  (fetchNuGet { pname = "Microsoft.NETCore.App.Runtime.linux-x64"; version = "8.0.1"; sha256 = "1g5b30f4l8a1zjjr3b8pk9mcqxkxqwa86362f84646xaj4iw3a4d"; })
  (fetchNuGet { pname = "SharpGLTF.Core"; version = "1.0.0-alpha0031"; sha256 = "0ln78mkhbcxqvwnf944hbgg24vbsva2jpih6q3x82d3h7rl1pkh6"; })
  (fetchNuGet { pname = "SharpGLTF.Runtime"; version = "1.0.0-alpha0031"; sha256 = "0lvb3asi3v0n718qf9y367km7qpkb9wci38y880nqvifpzllw0jg"; })
  (fetchNuGet { pname = "Sledge.Formats"; version = "1.2.2"; sha256 = "1y0l66m9rym0p1y4ifjlmg3j9lsmhkvbh38frh40rpvf1axn2dyh"; })
  (fetchNuGet { pname = "Sledge.Formats.Map"; version = "1.1.5"; sha256 = "1bww60hv9xcyxpvkzz5q3ybafdxxkw6knhv97phvpkw84pd0jil6"; })
  (fetchNuGet { pname = "System.Numerics.Vectors"; version = "4.5.0"; sha256 = "1kzrj37yzawf1b19jq0253rcs8hsq1l2q8g69d7ipnhzb0h97m59"; })
]

Finally, you move the deps.nix file to the appropriate location to be used by nugetDeps, then you're all set!

If you ever need to update the dependencies of a package, you instead do

nix-build -A package.fetch-deps to generate the update script for package
Run ./result to regenerate the lockfile to the path passed for nugetDeps (keep in mind if it can't be resolved to a local path, the script will write to $1 or a temporary path instead)
Finally, ensure the correct file was written and the derivation can be built.

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