From 6aa4f135c9f6660d2666c531aea405e9a7834852 Mon Sep 17 00:00:00 2001
From: jochen <jschoubben@gmail.com>
Date: Thu, 22 Oct 2026 01:22:31 +0200
Subject: [PATCH] Leave the go.mod fixtures under testdata out of the build
 module's tests and digests, so the checker stops running a fixture as a
 module (issue 1810)

---
 .../mesh-build-go/cmd/mesh-build-go/fetch.go  | 13 ++++++++-
 .../cmd/mesh-build-go/gomoddirs_test.go       | 27 +++++++++++++++++++
 .../mesh-build-go/cmd/mesh-build-go/recipe.go |  2 +-
 3 files changed, 40 insertions(+), 2 deletions(-)
 create mode 100644 modules/mesh-build-go/cmd/mesh-build-go/gomoddirs_test.go

diff --git a/modules/mesh-build-go/cmd/mesh-build-go/fetch.go b/modules/mesh-build-go/cmd/mesh-build-go/fetch.go
index 98462762..a6f1ef7c 100644
--- a/modules/mesh-build-go/cmd/mesh-build-go/fetch.go
+++ b/modules/mesh-build-go/cmd/mesh-build-go/fetch.go
@@ -145,7 +145,7 @@ func (m *Module) goModDirs(ctx context.Context, tree string) ([]string, error) {
 	}
 	dirs := []string{}
 	for _, l := range strings.Split(r.Stdout, "\n") {
-		if l = strings.TrimSpace(l); l != "" {
+		if l = strings.TrimSpace(l); l != "" && !inTestdata(l) {
 			dirs = append(dirs, filepath.ToSlash(filepath.Dir(l)))
 		}
 	}
@@ -153,6 +153,17 @@ func (m *Module) goModDirs(ctx context.Context, tree string) ([]string, error) {
 	return dirs, nil
 }
 
+// inTestdata says a path lies under a directory named testdata, whose go.mod files are fixtures Go ignores, not modules
+// of the tree (issue 1810).
+func inTestdata(path string) bool {
+	for _, seg := range strings.Split(filepath.ToSlash(path), "/") {
+		if seg == "testdata" {
+			return true
+		}
+	}
+	return false
+}
+
 // goEnv is what a go command of a step is given beyond the base environment: the installed go alone (GOTOOLCHAIN=local, ADR 0477 §1: no toolchain is ever downloaded),
 // modules resolved by their go.mod and go.sum, the module's own caches, the mesh's own modules fetched directly (by
 // git, through the account's rewrite of the forge's address to ssh), and nothing that asks a question. For a directory
diff --git a/modules/mesh-build-go/cmd/mesh-build-go/gomoddirs_test.go b/modules/mesh-build-go/cmd/mesh-build-go/gomoddirs_test.go
new file mode 100644
index 00000000..dfd9bb67
--- /dev/null
+++ b/modules/mesh-build-go/cmd/mesh-build-go/gomoddirs_test.go
@@ -0,0 +1,27 @@
+package main
+
+import (
+	"context"
+	"reflect"
+	"testing"
+
+	"git.novox.be/novox/mesh-sdk/go/forgekey"
+)
+
+// 1810/AC1: the go.mod files under a testdata directory are fixtures Go itself ignores, not modules of the tree, so
+// the build modules neither test nor digest them (a repository holding this module held one whose test reads
+// MESH_CHECK_BESIDE, which failed every check of it).
+func TestGoModDirsLeaveOutTheFixturesUnderTestdata(t *testing.T) {
+	m := &Module{}
+	m.Run = func(ctx context.Context, env []string, name string, args ...string) forgekey.Ran {
+		return forgekey.Ran{Stdout: "checks/deps/go.mod\ngo.mod\nmodules/x/cmd/x/testdata/repos/beside/go.mod\nmodules/x/go.mod\ntestdata/go.mod\n"}
+	}
+	got, err := m.goModDirs(context.Background(), t.TempDir())
+	if err != nil {
+		t.Fatal(err)
+	}
+	want := []string{".", "checks/deps", "modules/x"}
+	if !reflect.DeepEqual(got, want) {
+		t.Fatalf("go.mod directories = %v, want %v", got, want)
+	}
+}
diff --git a/modules/mesh-build-go/cmd/mesh-build-go/recipe.go b/modules/mesh-build-go/cmd/mesh-build-go/recipe.go
index 7a5c76f6..dc22a616 100644
--- a/modules/mesh-build-go/cmd/mesh-build-go/recipe.go
+++ b/modules/mesh-build-go/cmd/mesh-build-go/recipe.go
@@ -20,7 +20,7 @@ const PostgresMajor = 18
 
 // RecipeSteps is the recipe's own version: changed whenever the steps of fetch, test or build change in a way
 // that can change what they produce (ADR 0405 §7). It is one of the three values the recipe version hashes.
-const RecipeSteps = "1"
+const RecipeSteps = "2"
 
 // natsModule is the library the integration level's bus is started from (ADR 0470 §2).
 const natsModule = "github.com/nats-io/nats-server/v2"