<section xmlns="http://docbook.org/ns/docbook"
         xmlns:xlink="http://www.w3.org/1999/xlink"
         xml:id="sec-language-go">
 <title>Go</title>

 <section xml:id="ssec-go-modules">
  <title>Go modules</title>

  <para>
   The function <varname> buildGoModule </varname> builds Go programs managed with Go modules. It builds a <link xlink:href="https://github.com/golang/go/wiki/Modules">Go modules</link> through a two phase build:
   <itemizedlist>
    <listitem>
     <para>
      An intermediate fetcher derivation. This derivation will be used to fetch all of the dependencies of the Go module.
     </para>
    </listitem>
    <listitem>
     <para>
      A final derivation will use the output of the intermediate derivation to build the binaries and produce the final output.
     </para>
    </listitem>
   </itemizedlist>
  </para>

  <example xml:id='ex-buildGoModule'>
   <title>buildGoModule</title>
<programlisting>
pet = buildGoModule rec {
  pname = "pet";
  version = "0.3.4";

  src = fetchFromGitHub {
    owner = "knqyf263";
    repo = "pet";
    rev = "v${version}";
    sha256 = "0m2fzpqxk7hrbxsgqplkg7h2p7gv6s1miymv3gvw0cz039skag0s";
  };

  vendorSha256 = "1879j77k96684wi554rkjxydrj8g3hpp0kvxz03sd8dmwr3lh83j"; <co xml:id='ex-buildGoModule-1' />

  subPackages = [ "." ]; <co xml:id='ex-buildGoModule-2' />

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

  <para>
   <xref linkend='ex-buildGoModule'/> is an example expression using buildGoModule, the following arguments are of special significance to the function:
   <calloutlist>
    <callout arearefs='ex-buildGoModule-1'>
     <para>
      <varname>vendorSha256</varname> is the hash of the output of the intermediate fetcher derivation.
     </para>
    </callout>
    <callout arearefs='ex-buildGoModule-2'>
     <para>
      <varname>subPackages</varname> limits the builder from building child packages that have not been listed. If <varname>subPackages</varname> is not specified, all child packages will be built.
     </para>
    </callout>
   </calloutlist>
  </para>

  <para>
    <varname>vendorSha256</varname> can also take <varname>null</varname> as an input.

    When `null` is used as a value, rather than fetching the dependencies
    and vendoring them, we use the vendoring included within the source repo.
    If you'd like to not have to update this field on dependency changes, 
    run `go mod vendor` in your source repo and set 'vendorSha256 = null;'
  </para>
 </section>

 <section xml:id="ssec-go-legacy">
  <title>Go legacy</title>

  <para>
   The function <varname> buildGoPackage </varname> builds legacy Go programs, not supporting Go modules.
  </para>

  <example xml:id='ex-buildGoPackage'>
   <title>buildGoPackage</title>
<programlisting>
deis = buildGoPackage rec {
  pname = "deis";
  version = "1.13.0";

  goPackagePath = "github.com/deis/deis"; <co xml:id='ex-buildGoPackage-1' />
  subPackages = [ "client" ]; <co xml:id='ex-buildGoPackage-2' />

  src = fetchFromGitHub {
    owner = "deis";
    repo = "deis";
    rev = "v${version}";
    sha256 = "1qv9lxqx7m18029lj8cw3k7jngvxs4iciwrypdy0gd2nnghc68sw";
  };

  goDeps = ./deps.nix; <co xml:id='ex-buildGoPackage-3' />

  buildFlags = [ "--tags" "release" ]; <co xml:id='ex-buildGoPackage-4' />
}
</programlisting>
  </example>

  <para>
   <xref linkend='ex-buildGoPackage'/> is an example expression using buildGoPackage, the following arguments are of special significance to the function:
   <calloutlist>
    <callout arearefs='ex-buildGoPackage-1'>
     <para>
      <varname>goPackagePath</varname> specifies the package's canonical Go import path.
     </para>
    </callout>
    <callout arearefs='ex-buildGoPackage-2'>
     <para>
      <varname>subPackages</varname> limits the builder from building child packages that have not been listed. If <varname>subPackages</varname> is not specified, all child packages will be built.
     </para>
     <para>
      In this example only <literal>github.com/deis/deis/client</literal> will be built.
     </para>
    </callout>
    <callout arearefs='ex-buildGoPackage-3'>
     <para>
      <varname>goDeps</varname> 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 <varname>deps.nix</varname> file for readability. The dependency data structure is described below.
     </para>
    </callout>
    <callout arearefs='ex-buildGoPackage-4'>
     <para>
      <varname>buildFlags</varname> is a list of flags passed to the go build command.
     </para>
    </callout>
   </calloutlist>
  </para>

  <para>
   The <varname>goDeps</varname> attribute can be imported from a separate <varname>nix</varname> file that defines which Go libraries are needed and should be included in <varname>GOPATH</varname> for <varname>buildPhase</varname>.
  </para>

  <example xml:id='ex-goDeps'>
   <title>deps.nix</title>
<programlisting>
[ <co xml:id='ex-goDeps-1' />
  {
    goPackagePath = "gopkg.in/yaml.v2"; <co xml:id='ex-goDeps-2' />
    fetch = {
      type = "git"; <co xml:id='ex-goDeps-3' />
      url = "https://gopkg.in/yaml.v2";
      rev = "a83829b6f1293c91addabc89d0571c246397bbf4";
      sha256 = "1m4dsmk90sbi17571h6pld44zxz7jc4lrnl4f27dpd1l8g5xvjhh";
    };
  }
  {
    goPackagePath = "github.com/docopt/docopt-go";
    fetch = {
      type = "git";
      url = "https://github.com/docopt/docopt-go";
      rev = "784ddc588536785e7299f7272f39101f7faccc3f";
      sha256 = "0wwz48jl9fvl1iknvn9dqr4gfy1qs03gxaikrxxp9gry6773v3sj";
    };
  }
]
</programlisting>
  </example>

  <para>
   <calloutlist>
    <callout arearefs='ex-goDeps-1'>
     <para>
      <varname>goDeps</varname> is a list of Go dependencies.
     </para>
    </callout>
    <callout arearefs='ex-goDeps-2'>
     <para>
      <varname>goPackagePath</varname> specifies Go package import path.
     </para>
    </callout>
    <callout arearefs='ex-goDeps-3'>
     <para>
      <varname>fetch type</varname> that needs to be used to get package source. If <varname>git</varname> is used there should be <varname>url</varname>, <varname>rev</varname> and <varname>sha256</varname> defined next to it.
     </para>
    </callout>
   </calloutlist>
  </para>

  <para>
   To extract dependency information from a Go package in automated way use <link xlink:href="https://github.com/kamilchm/go2nix">go2nix</link>. It can produce complete derivation and <varname>goDeps</varname> file for Go programs.
  </para>

  <para>
   You may use Go packages installed into the active Nix profiles by adding the following to your ~/.bashrc:
<screen>
for p in $NIX_PROFILES; do
    GOPATH="$p/share/go:$GOPATH"
done
</screen>
  </para>
 </section>
</section>
