buildGoModule: don't inherit build hooks when building go-modules (#225349)

* buildGoModule: don't inherit postBuild hook when building go-modules

This is a slight revert of 5ce647b8bf7aee0d3862006d94df7878c7fc03a6
(#212800).

Inheriting these hooks in the `.go-modules` derivation can be confusing:
One doesn't expect them to run when generating the fixed output modules
derivation, but only on the main derivation. A `postBuild` hook that
adds some files to $out will cause a very hard to debug issue[1].

This commit adds support for a dedicated `modPostBuild` hook that will
be used only by the derivation building `.go-modules`. Additionally,
`go.section.md` now explains these attributes behavior better.

[1]:
https://discourse.nixos.org/t/cant-update-a-go-package-getting-go-inconsistent-vendoring/27063/6

Co-authored-by: Sandro <sandro.jaeckel@gmail.com>

1 files changed, 5 insertions, 1 deletions

diff --git a/pkgs/build-support/go/module.nix b/pkgs/build-support/go/module.nix
index 045ce11fe01..2c5d1827cde 100644
--- a/pkgs/build-support/go/module.nix
+++ b/pkgs/build-support/go/module.nix
@@ -83,12 +83,16 @@ let
     inherit (args) src;
     inherit (go) GOOS GOARCH;
 
+    # The following inheritence behavior is not trivial to expect, and some may
+    # argue it's not ideal. Changing it may break vendor hashes in Nixpkgs and
+    # out in the wild. In anycase, it's documented in:
+    # doc/languages-frameworks/go.section.md
     prePatch = args.prePatch or "";
     patches = args.patches or [];
     patchFlags = args.patchFlags or [];
     postPatch = args.postPatch or "";
     preBuild = args.preBuild or "";
-    postBuild = args.postBuild or "";
+    postBuild = args.modPostBuild or "";
     sourceRoot = args.sourceRoot or "";
 
     GO111MODULE = "on";