Take a walk's key in again when it was recorded at an earlier merge, so the module is registered at the commit the walk carries before it is built (issue 1851, A6)

cmd/mesh-controller/plan_keys.go

@@ -160,13 +160,13 @@ func settleKeys(ctx context.Context, inv keyRecords, keys planKeyReads, p *inven
 			keyTakes.Unlock()
 			registered := taken
 			if !registered {
-				if registered, err = registeredFrom(ctx, inv, m, b); err != nil {
+				if registered, err = registeredAt(ctx, inv, m, trunk.Commit); err != nil {
 					return changed, err
 				}
 			}
 			if registered {
 				at := b.At
-				s.State, s.BuiltAt, s.Commit, s.Build = "built", &at, b.Commit, id
+				s.State, s.BuiltAt, s.Commit, s.Build = "built", &at, trunk.Commit, id
 				s.Made = fmt.Sprintf("taken from the builder's key %s (revision %d), no build asked", short(trunk.FP2), k.Revision)
 				s.Why = ""
 				fmt.Printf("%s: %s taken from the builder's key %s\n", p.ID, m, short(trunk.FP2))
@@ -192,9 +192,10 @@ func settleKeys(ctx context.Context, inv keyRecords, keys planKeyReads, p *inven
 	return changed, nil
 }
 
-// registeredFrom says the module's registration stands on the build: the catalogue holds the module at the build's
-// commit, or the build was registered as one with an unchanged source (no move).
-func registeredFrom(ctx context.Context, inv keyRecords, module string, b inventory.Build) (bool, error) {
+// registeredAt says the catalogue holds the module registered at the commit the walk takes it at: its key's take-in
+// registered it there, whether with the key's artifacts or, unchanged, with the build it stands on (no move). A key
+// recorded at an earlier commit (the same fingerprint at an older merge) is taken in again, to register it here.
+func registeredAt(ctx context.Context, inv keyRecords, module, commit string) (bool, error) {
 	src, err := inv.SourceOf(ctx, module)
 	if errors.Is(err, inventory.ErrNoSuchModule) {
 		return false, nil
@@ -202,7 +203,7 @@ func registeredFrom(ctx context.Context, inv keyRecords, module string, b invent
 	if err != nil {
 		return false, err
 	}
-	return sameCommitID(src.BuiltFrom, b.Commit), nil
+	return sameCommitID(src.BuiltFrom, commit), nil
 }
 
 func sameCommitID(a, b string) bool {

cmd/mesh-controller/plan_keys_test.go

@@ -188,3 +188,33 @@ func TestARefusedTakeInFailsTheWalk(t *testing.T) {
 		t.Fatalf("a refused take-in did not fail the walk: %s %q", p.State, p.Note)
 	}
 }
+
+// A6: a walk's module whose fingerprint did not change since an earlier merge has its key recorded at that merge's
+// commit: the walk takes it in again, so the module is registered at the commit the walk carries, before it is built.
+func TestAKeyRecordedAtAnEarlierCommitIsTakenInAgain(t *testing.T) {
+	t.Cleanup(func() {
+		keyTakes.Lock()
+		keyTakes.running, keyTakes.waits, keyTakes.taken = map[string]bool{}, map[string]string{}, map[string]bool{}
+		keyTakes.Unlock()
+	})
+	p, byName := aWalkOfOne("sudo")
+	askModule(t.Context(), p, "sudo", byName)
+	fp := "src2:" + strings.Repeat("e", 64)
+	k := builderkeys.Key{Module: "sudo", Fingerprint: fp, Found: true, Revision: 1, Build: sdkdelivery.BuilderBuild{
+		State: sdkdelivery.BuildDone, Manifest: strings.Repeat("b", 64), Artifacts: []sdkdelivery.BuiltArtifact{{Name: "a",
+			Digest: "sha256:1", Reference: "artifact-store://sudo/a/blobs/sha256:1"}}}}
+	keys := planKeysOf{values: map[string]sdkdelivery.Module{"sudo@c0ffee0123456789": {FP2: fp, Commit: "c0ffee0123456789"}},
+		keys: map[string]builderkeys.Key{"sudo": k}}
+	id := keyBuildID(k)
+	records := recordsOf{builds: map[string]inventory.Build{id: {ID: id, Module: "sudo", Commit: "0ld0ld0ld0ld"}},
+		sources: map[string]inventory.Source{"sudo": {BuiltFrom: "0ld0ld0ld0ld"}}}
+	var taken []string
+	if _, err := settleKeys(t.Context(), records, keys, p, p.Tiers[0], func(m string, _ sdkdelivery.Module, _ string) {
+		taken = append(taken, m)
+	}); err != nil {
+		t.Fatal(err)
+	}
+	if s := p.Modules["sudo"]; s.State != "asked" || len(taken) != 1 {
+		t.Fatalf("a key recorded at an earlier commit settled the walk at that commit: %+v, taken %v", s, taken)
+	}
+}