depot/doc/languages-frameworks/go.section.md

Go

Building Go modules with buildGoModule

The function buildGoModule builds Go programs managed with Go modules. It builds Go Modules through a two phase build:

• An intermediate fetcher derivation called goModules. This derivation will be used to fetch all the dependencies of the Go module.
• A final derivation will use the output of the intermediate derivation to build the binaries and produce the final output.

Attributes of buildGoModule

The buildGoModule function accepts the following parameters in addition to the attributes accepted by both Go builders:

• vendorHash: is the hash of the output of the intermediate fetcher derivation (the dependencies of the Go modules).

  vendorHash can be set to null. In that case, rather than fetching the dependencies, the dependencies already vendored in the vendor directory of the source repo will be used.

  To avoid updating this field when dependencies change, run go mod vendor in your source repo and set vendorHash = null;. You can read more about vendoring in the Go documentation.

  To obtain the actual hash, set vendorHash = lib.fakeHash; and run the build (more details here).

• proxyVendor: If true, the intermediate fetcher downloads dependencies from the Go module proxy (using go mod download) instead of vendoring them. The resulting module cache is then passed to the final derivation.

  This is useful if your code depends on C code and go mod tidy does not include the needed sources to build or if any dependency has case-insensitive conflicts which will produce platform-dependent vendorHash checksums.

  Defaults to false.

• modPostBuild: Shell commands to run after the build of the goModules executes go mod vendor, and before calculating fixed output derivation's vendorHash. Note that if you change this attribute, you need to update vendorHash attribute.

• modRoot: The root directory of the Go module that contains the go.mod file. Defaults to ./, which is the root of src.

Example for buildGoModule

The following is an example expression using buildGoModule:

{
  pet = buildGoModule rec {
    pname = "pet";
    version = "0.3.4";

    src = fetchFromGitHub {
      owner = "knqyf263";
      repo = "pet";
      rev = "v${version}";
      hash = "sha256-Gjw1dRrgM8D3G7v6WIM2+50r4HmTXvx0Xxme2fH9TlQ=";
    };

    vendorHash = "sha256-ciBIR+a1oaYH+H1PcC8cD8ncfJczk1IiJ8iYNM+R6aA=";

    meta = {
      description = "Simple command-line snippet manager, written in Go";
      homepage = "https://github.com/knqyf263/pet";
      license = lib.licenses.mit;
      maintainers = with lib.maintainers; [ kalbasit ];
    };
  };
}

Obtaining and overriding vendorHash for buildGoModule

We can use nix-prefetch to obtain the actual hash. The following command gets the value of vendorHash for package pet:

cd path/to/nixpkgs
nix-prefetch -E "{ sha256 }: ((import ./. { }).my-package.overrideAttrs { vendorHash = sha256; }).goModules"

To obtain the hash without external tools, set vendorHash = lib.fakeHash; and run the build. (more details here).

vendorHash can be overridden with overrideAttrs. Override the above example like this:

{
  pet_0_4_0 = pet.overrideAttrs (
    finalAttrs: previousAttrs: {
      version = "0.4.0";
      src = fetchFromGitHub {
        inherit (previousAttrs.src) owner repo;
        rev = "v${finalAttrs.version}";
        hash = "sha256-gVTpzmXekQxGMucDKskGi+e+34nJwwsXwvQTjRO6Gdg=";
      };
      vendorHash = "sha256-dUvp7FEW09V0xMuhewPGw3TuAic/sD7xyXEYviZ2Ivs=";
    }
  );
}

Overriding goModules

Overriding <pkg>.goModules by calling goModules.overrideAttrs is unsupported. Still, it is possible to override the vendorHash (goModules's outputHash) and the pre/post hooks for both the build and patch phases of the primary and goModules derivation. Alternatively, the primary derivation provides an overridable passthru.overrideModAttrs function to store the attribute overlay implicitly taken by goModules.overrideAttrs. Here's an example usage of overrideModAttrs:

{
  pet-overridden = pet.overrideAttrs (
    finalAttrs: previousAttrs: {
      passthru = previousAttrs.passthru // {
        # If the original package has an `overrideModAttrs` attribute set, you'd
        # want to extend it, and not replace it. Hence we use
        # `lib.composeExtensions`. If you are sure the `overrideModAttrs` of the
        # original package trivially does nothing, you can safely replace it
        # with your own by not using `lib.composeExtensions`.
        overrideModAttrs = lib.composeExtensions previousAttrs.passthru.overrideModAttrs (
          finalModAttrs: previousModAttrs: {
            # goModules-specific overriding goes here
            postBuild = ''
              # Here you have access to the `vendor` directory.
              substituteInPlace vendor/github.com/example/repo/file.go \
                --replace-fail "panic(err)" ""
            '';
          }
        );
      };
    }
  );
}

buildGoPackage (legacy)

The function buildGoPackage builds legacy Go programs, not supporting Go modules.

::: {.warning} buildGoPackage is deprecated and will be removed for the 25.05 release. :::

Migrating from buildGoPackage to buildGoModule

Go modules, released 6y ago, are now widely adopted in the ecosystem. Most upstream projects are using Go modules, and the tooling previously used for dependency management in Go is mostly deprecated, archived or at least unmaintained at this point.

In case a project doesn't have external dependencies or dependencies are vendored in a way understood by go mod init, migration can be done with a few changes in the package.

• Switch the builder from buildGoPackage to buildGoModule
• Remove goPackagePath and other attributes specific to buildGoPackage
• Set vendorHash = null;
• Run go mod init <module name> in postPatch

In case the package has external dependencies that aren't vendored or the build setup is more complex the upstream source might need to be patched. Examples for the migration can be found in the issue tracking migration withing nixpkgs.

Example for buildGoPackage

In the following is an example expression using buildGoPackage, the following arguments are of special significance to the function:

• goPackagePath specifies the package's canonical Go import path.
• goDeps is where the Go dependencies of a Go program are listed as a list of package source identified by Go import path. It could be imported as a separate deps.nix file for readability. The dependency data structure is described below.

{
  deis = buildGoPackage rec {
    pname = "deis";
    version = "1.13.0";

    goPackagePath = "github.com/deis/deis";

    src = fetchFromGitHub {
      owner = "deis";
      repo = "deis";
      rev = "v${version}";
      hash = "sha256-XCPD4LNWtAd8uz7zyCLRfT8rzxycIUmTACjU03GnaeM=";
    };

    goDeps = ./deps.nix;
  };
}

The goDeps attribute can be imported from a separate nix file that defines which Go libraries are needed and should be included in GOPATH for buildPhase:

# deps.nix
[ # goDeps is a list of Go dependencies.
  {
    # goPackagePath specifies Go package import path.
    goPackagePath = "gopkg.in/yaml.v2";
    fetch = {
      # `fetch type` that needs to be used to get package source.
      # If `git` is used there should be `url`, `rev` and `hash` defined next to it.
      type = "git";
      url = "https://gopkg.in/yaml.v2";
      rev = "a83829b6f1293c91addabc89d0571c246397bbf4";
      hash = "sha256-EMrdy0M0tNuOcITaTAmT5/dPSKPXwHDKCXFpkGbVjdQ=";
    };
  }
  {
    goPackagePath = "github.com/docopt/docopt-go";
    fetch = {
      type = "git";
      url = "https://github.com/docopt/docopt-go";
      rev = "784ddc588536785e7299f7272f39101f7faccc3f";
      hash = "sha256-Uo89zjE+v3R7zzOq/gbQOHj3SMYt2W1nDHS7RCUin3M=";
    };
  }
]

To extract dependency information from a Go package in automated way use go2nix (deprecated). It can produce complete derivation and goDeps file for Go programs.

You may use Go packages installed into the active Nix profiles by adding the following to your ~/.bashrc:

for p in $NIX_PROFILES; do
    GOPATH="$p/share/go:$GOPATH"
done

Attributes used by both builders

Many attributes controlling the build phase are respected by both buildGoModule and buildGoPackage. Note that buildGoModule reads the following attributes also when building the vendor/ goModules fixed output derivation as well:

• sourceRoot
• prePatch
• patches
• patchFlags
• postPatch
• preBuild
• env: useful for passing down variables such as GOWORK.

To control test execution of the build derivation, the following attributes are of interest:

• checkInputs
• preCheck
• checkFlags

In addition to the above attributes, and the many more variables respected also by stdenv.mkDerivation, both buildGoModule and buildGoPackage respect Go-specific attributes that tweak them to behave slightly differently:

ldflags

A string list of flags to pass to the Go linker tool via the -ldflags argument of go build. Possible values can be retrieved by running go tool link --help. The most common use case for this argument is to make the resulting executable aware of its own version by injecting the value of string variable using the -X flag. For example:

{
  ldflags = [
    "-X main.Version=${version}"
    "-X main.Commit=${version}"
  ];
}

tags

A string list of Go build tags (also called build constraints) that are passed via the -tags argument of go build. These constraints control whether Go files from the source should be included in the build. For example:

{
  tags = [
    "production"
    "sqlite"
  ];
}

Tags can also be set conditionally:

{
  tags = [ "production" ] ++ lib.optionals withSqlite [ "sqlite" ];
}

deleteVendor

If set to true, removes the pre-existing vendor directory. This should only be used if the dependencies included in the vendor folder are broken or incomplete.

subPackages

Specified as a string or list of strings. Limits the builder from building child packages that have not been listed. If subPackages is not specified, all child packages will be built.

Many Go projects keep the main package in a cmd directory. Following example could be used to only build the example-cli and example-server binaries:

{
  subPackages = [
    "cmd/example-cli"
    "cmd/example-server"
  ];
}

excludedPackages

Specified as a string or list of strings. Causes the builder to skip building child packages that match any of the provided values.

CGO_ENABLED

When set to 0, the cgo command is disabled. As consequence, the build program can't link against C libraries anymore, and the resulting binary is statically linked.

When building with CGO enabled, Go will likely link some packages from the Go standard library against C libraries, even when the target code does not explicitly call into C dependencies. With CGO_ENABLED = 0;, Go will always use the Go native implementation of these internal packages. For reference see net and os/user packages. Notice that the decision whether these packages should use native Go implementation or not can also be controlled on a per package level using build tags (tags). In case CGO is disabled, these tags have no additional effect.

When a Go program depends on C libraries, place those dependencies in buildInputs:

{
  buildInputs = [
    libvirt
    libxml2
  ];
}

CGO_ENABLED defaults to 1.

enableParallelBuilding

Whether builds and tests should run in parallel.

Defaults to true.

allowGoReference

Whether the build result should be allowed to contain references to the Go tool chain. This might be needed for programs that are coupled with the compiler, but shouldn't be set without a good reason.

Defaults to false

Controlling the Go environment

The Go build can be further tweaked by setting environment variables. In most cases, this isn't needed. Possible values can be found in the Go documentation of accepted environment variables. Notice that some of these flags are set by the builder itself and should not be set explicitly. If in doubt, grep the implementation of the builder.

Skipping tests

buildGoModule runs tests by default. Failing tests can be disabled using the checkFlags parameter. This is done with the -skip or -run flags of the go test command.

For example, only a selection of tests could be run with:

{
  # -run and -skip accept regular expressions
  checkFlags = [
    "-run=^Test(Simple|Fast)$"
  ];
}

If a larger amount of tests should be skipped, the following pattern can be used:

{
  checkFlags =
    let
      # Skip tests that require network access
      skippedTests = [
        "TestNetwork"
        "TestDatabase/with_mysql" # exclude only the subtest
        "TestIntegration"
      ];
    in
    [ "-skip=^${builtins.concatStringsSep "$|^" skippedTests}$" ];
}

To disable tests altogether, set doCheck = false;. buildGoPackage does not execute tests by default.