Skip the trunk comparison, saying NOT COMPARED, when the catalogue's own copy is not beside: the checker before R4g places none, so R4g's own check could never pass (issue 1295)

checks/trunk/trunk.go

@@ -3,8 +3,9 @@
 //
 // The checker fetches the change's own repository at its base commit beside the change, as it fetches a sibling, and says where
 // in MESH_CHECK_BESIDE; the copy is under the repository's name (the same convention the other repositories' tests use). With
-// MESH_CHECK_BESIDE unset the comparison is skipped, and the test says NOT COMPARED WITH THE TRUNK. Set, without the catalogue's
-// copy in it, the test fails loudly: a check that cannot compare must not look as if it had. A trunk that holds no such file had
+// MESH_CHECK_BESIDE unset, or set without the catalogue's copy in it, the comparison is skipped and the test says NOT COMPARED
+// WITH THE TRUNK, naming why: the checker that runs before R4g's delivery places siblings but not the change's own repository,
+// so R4g's own check cannot hold the copy (issue 1295 notes that a missing copy becomes a failure once that checker is gone). A trunk that holds no such file had
 // none: the list's first copy, which nothing was added to.
 package trunk
 
@@ -22,8 +23,7 @@ const Repository = "mesh-catalog"
 const BesideEnv = "MESH_CHECK_BESIDE"
 
 // Copy is the trunk's copy of the file at rel (a path from the catalogue's root), written to a file of the test's own: its path,
-// and whether the trunk holds one (false: its first copy). It skips the test when no trunk is beside, and fails it when the
-// directory is named and holds no copy of the catalogue.
+// and whether the trunk holds one (false: its first copy). It skips the test, saying so, when no copy of the catalogue is beside.
 func Copy(t testing.TB, rel string) (string, bool) {
 	t.Helper()
 	raw, found, skip, err := Read(rel)
@@ -52,9 +52,11 @@ func Read(rel string) (content []byte, found bool, skip string, err error) {
 			" is not beside this run; the checker places it", nil
 	}
 	dir := filepath.Join(beside, Repository)
-	if _, err := os.Stat(dir); err != nil {
-		return nil, false, "", errors.New(Repository + " is not beside this check in " + BesideEnv + "=" + beside +
-			", so " + rel + " cannot be judged against the trunk's copy: " + err.Error())
+	if _, err := os.Stat(dir); errors.Is(err, os.ErrNotExist) {
+		return nil, false, "NOT COMPARED WITH THE TRUNK: " + Repository + " is not beside this check in " + BesideEnv + "=" + beside +
+			", so " + rel + " is not judged against the trunk's copy (the checker before R4g places no copy of the change's own repository)", nil
+	} else if err != nil {
+		return nil, false, "", err
 	}
 	raw, err := os.ReadFile(filepath.Join(dir, rel))
 	if errors.Is(err, os.ErrNotExist) {

checks/trunk/trunk_test.go

@@ -3,6 +3,7 @@ package trunk
 import (
 	"os"
 	"path/filepath"
+	"strings"
 	"testing"
 )
 
@@ -33,9 +34,10 @@ func TestWithNothingBesideTheComparisonIsSkippedAndSaidNotMade(t *testing.T) {
 	}
 }
 
-func TestACloneBesideWithoutTheCatalogueFailsLoudly(t *testing.T) {
-	t.Setenv(BesideEnv, t.TempDir()) // the siblings are there, the catalogue's own base is not
-	if _, _, skip, err := Read("checks/x/known"); err == nil || skip != "" {
-		t.Fatalf("skip %q err %v; wanted an error", skip, err)
+func TestACloneBesideWithoutTheCatalogueIsSkippedAndSaidNotMade(t *testing.T) {
+	t.Setenv(BesideEnv, t.TempDir()) // the siblings are there, the catalogue's own base is not (the checker before R4g)
+	_, found, skip, err := Read("checks/x/known")
+	if found || err != nil || len(skip) < 12 || skip[:12] != "NOT COMPARED" || !strings.Contains(skip, "not beside") {
+		t.Fatalf("found %v, skip %q, err %v; wanted NOT COMPARED naming the missing copy", found, skip, err)
 	}
 }