12 KiB
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.
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 ];
};
};
}
Attributes of buildGoModule
Many attributes controlling the build phase are respected by buildGoModule
. 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 asGOWORK
.
To control test execution of the build derivation, the following attributes are of interest:
In addition to the above attributes, and the many more variables respected also by stdenv.mkDerivation
, buildGoModule
respects Go-specific attributes that tweak them to behave slightly differently:
vendorHash
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 hash, set vendorHash = lib.fakeHash;
and run the build. (more details here).
Another way is to use use nix-prefetch
to obtain the 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"
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=";
}
);
}
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
.
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
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)" ""
'';
}
);
};
}
);
}
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;
.
Migrating from buildGoPackage
to buildGoModule
::: {.warning}
buildGoPackage
was removed for the 25.05 release. It was used to build legacy Go programs
that do not support Go modules.
:::
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
tobuildGoModule
- Remove
goPackagePath
and other attributes specific tobuildGoPackage
- Set
vendorHash = null;
- Run
go mod init <module name>
inpostPatch
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.