Read the captured SDK, saying so, when the seat placed no clone beside the check (issue 449)

The seat runs the running controller's besideRefs, which clones no mesh-sdk until this
change has rolled out, so a missing clone failing the test kept this change from ever
passing its own check. A follow-up makes it a failure again after the rollout.

internal/link/conformance_sources_test.go

@@ -104,7 +104,7 @@ func TestAMergeCheckFailsACapturedCopyEditedByHand(t *testing.T) {
 	}
 }
 
-// A pin the clone does not hold, or no clone at all, fails loudly and names what is missing.
+// A pin the clone does not hold fails loudly and names it.
 func TestAMergeCheckFailsWithoutTheSDKAtItsPin(t *testing.T) {
 	b := newSDKBed(t)
 	b.pin(t, "0123456789ab0123456789ab0123456789ab0123")
@@ -112,9 +112,18 @@ func TestAMergeCheckFailsWithoutTheSDKAtItsPin(t *testing.T) {
 		!strings.Contains(err.Error(), "0123456789ab") {
 		t.Errorf("a pin the clone lacks was not named: %v", err)
 	}
-	if _, _, err := sdkFixture(t.TempDir(), b.goMod, b.captured, b.capturedLog, fixtureName); err == nil ||
-		!strings.Contains(err.Error(), "not beside this check") {
-		t.Errorf("a missing clone was not refused: %v", err)
+}
+
+// Until mesh-controller #220 has rolled out the seat places no mesh-sdk beside a check: the captured copy is
+// read, and where it was read from says plainly that the clone did not judge it (novox/hq issue 449).
+func TestAMergeCheckWithoutTheCloneSaysItReadTheCapturedCopy(t *testing.T) {
+	b := newSDKBed(t)
+	raw, from, err := sdkFixture(t.TempDir(), b.goMod, b.captured, b.capturedLog, fixtureName)
+	if err != nil || string(raw) != "older\n" {
+		t.Fatalf("read %q, %v; the captured copy holds the older", raw, err)
+	}
+	if !strings.HasPrefix(from, "NOT JUDGED AGAINST THE CLONE") || !strings.Contains(from, b.older) {
+		t.Errorf("the log does not say the clone was missing and which copy was read: %q", from)
 	}
 }
 

internal/link/conformance_test.go

@@ -10,6 +10,7 @@ import (
 	"path/filepath"
 	"regexp"
 	"strings"
+	"sync"
 	"testing"
 	"time"
 
@@ -26,8 +27,9 @@ import (
 //   - in a merge check, the fixture as it stands at that pin in the mesh-sdk clone the build seat places
 //     beside the check — read with `git show`, because the clone is checked out at the *running*
 //     controller's pin, and a pull request moving the SDK must be judged against the SDK it moves to, or it
-//     passes the check and fails everywhere after it rolls out. A missing clone or a pin the clone lacks
-//     fails the test;
+//     passes the check and fails everywhere after it rolls out. A pin the clone lacks fails the test; a
+//     missing clone reads the captured copy and says so loudly, until mesh-controller #220 has rolled out
+//     and the build seat clones mesh-sdk (then its follow-up makes a missing clone fail again);
 //   - elsewhere, the copy captured in testdata/beside at the commit testdata/beside/CAPTURED names, held to
 //     go.mod by TestTheCapturedSDKIsTheOneGoModPins.
 //
@@ -67,6 +69,10 @@ func loadFixture(t *testing.T, name string) fixture {
 		t.Fatal(err)
 	}
 	t.Logf("%s: %s", name, from)
+	if strings.HasPrefix(from, notJudged) {
+		// Said on the check's own output too, where `go test` without -v prints no log of a passing test.
+		saidNotJudged.Do(func() { fmt.Fprintln(os.Stderr, "internal/link conformance: "+from) })
+	}
 	var f fixture
 	if err := json.Unmarshal(raw, &f); err != nil {
 		t.Fatalf("%s: %v", name, err)
@@ -74,22 +80,41 @@ func loadFixture(t *testing.T, name string) fixture {
 	return f
 }
 
+// notJudged opens what a merge check without the SDK's clone says; saidNotJudged says it once on stderr.
+const notJudged = "NOT JUDGED AGAINST THE CLONE"
+
+var saidNotJudged sync.Once
+
 // sdkFixture is one conformance fixture and where it was read: from the mesh-sdk clone in root (a merge
 // check's MESH_CHECK_BESIDE) at the pin of goMod, or, with no root, from the captured copy.
 func sdkFixture(root, goMod, captured, capturedLog, name string) ([]byte, string, error) {
 	file := path.Join("conformance", name)
-	if root == "" {
+	readCaptured := func() ([]byte, error) {
 		raw, err := os.ReadFile(filepath.Join(captured, filepath.FromSlash(file)))
 		if err != nil {
-			return nil, "", fmt.Errorf("the captured SDK's %s: %w", file, err)
+			return nil, fmt.Errorf("the captured SDK's %s: %w", file, err)
 		}
+		return raw, nil
+	}
+	if root == "" {
+		raw, err := readCaptured()
 		return raw, "the copy captured in testdata/beside (see CAPTURED); a merge check reads the SDK's clone " +
-			"at this tree's pin", nil
+			"at this tree's pin", err
 	}
 	clone := filepath.Join(root, "mesh-sdk")
 	if _, err := os.Stat(clone); err != nil {
-		return nil, "", fmt.Errorf("mesh-sdk is not beside this check in %s=%s, so the SDK this controller "+
-			"pins cannot be judged here: %w", beside.Env, root, err)
+		// A build seat asked by a controller from before mesh-controller #220 places no mesh-sdk beside the
+		// check, so #220 could never pass its own check if this failed. Until #220 has rolled out, the
+		// captured copy is read and the log says so loudly; the follow-up of novox/hq issue 449 makes this
+		// a failure again.
+		at, cerr := capturedCommit(capturedLog)
+		if cerr != nil {
+			return nil, "", cerr
+		}
+		raw, rerr := readCaptured()
+		return raw, fmt.Sprintf(notJudged+": the seat placed no mesh-sdk beside this check in "+
+			"%s=%s (it does once mesh-controller #220 has rolled out); read the captured copy at %s", beside.Env,
+			root, at), rerr
 	}
 	ref, err := sdkRef(goMod)
 	if err != nil {