buildGoModule: support impure modules (#76532)

When modSha256 is null, disable the nix sandbox instead of using a
fixed-output derivation. This requires the nix-daemon to have
`sandbox = relaxed` set in their config to work properly.

Because the output is (hopefully) deterministic based on the inputs,
this should give a reproducible output. This is useful for development
outside of nixpkgs where re-generating the modSha256 on each mod.sum
changes is cumbersome.

Don't use this in nixpkgs! This is why null is not the default value.

1 files changed, 9 insertions, 0 deletions

diff --git a/doc/languages-frameworks/go.xml b/doc/languages-frameworks/go.xml
index bd1ee8eba27..53c891e66f8 100644
--- a/doc/languages-frameworks/go.xml
+++ b/doc/languages-frameworks/go.xml
@@ -66,6 +66,15 @@ pet = buildGoModule rec {
     </callout>
    </calloutlist>
   </para>
+
+  <para>
+    <varname>modSha256</varname> can also take <varname>null</varname> as an input.
+
+    When `null` is used as a value, the derivation won't be a
+    fixed-output derivation but disable the build sandbox instead. This can be useful outside
+    of nixpkgs where re-generating the modSha256 on each mod.sum changes is cumbersome,
+    but will fail to build by Hydra, as builds with a disabled sandbox are discouraged.
+  </para>
  </section>
 
  <section xml:id="ssec-go-legacy">