Let a merge that shares nothing skip the merge window (hq issue 525)

A merge waited the whole window even when nothing assembling shared anything
with it. It now joins only a batch it is related to (ADR 0304 §1, read by ADR
0306 §3: repository, a module the cut would move, a graph edge, a group head),
folding the newer into the oldest when it relates to two. A merge related to
none starts a batch whose window is closed at once (PlanBatch.CutAtOnce),
unless its delivery group may still have a member to merge (ADR 0306 §2).

The controller cannot see a group's unmerged members (that is mesh-delivery's
record), so a merge from any head still waits, in a batch of its own: the safe
error is to wait. Walks stay one at a time; a batch cut at once queues behind
an open walk. A stop's merges walked again join a related batch, or their own.

cmd/mesh-controller/batches_test.go

@@ -58,19 +58,36 @@ func windowed(t *testing.T) *stores {
 // t0 is the moment a test's clock starts: merges are dated by it, and heard after it.
 var t0 = time.Now().UTC().Truncate(time.Second)
 
-// catalogueMerge is a merge of the catalogue changing one module's directory, made at a moment.
+// catalogueMerge is a merge of the catalogue changing one module's directory, made at a moment, from a pull
+// request's head branch of its own, as the forge announces every merge. A merge from a head may have a group
+// member still to merge, which the controller cannot tell, so it waits for the window (novox/hq ADR 0306
+// decision 2, stillAssembles): these merges keep the window's rules of ADR 0276. lone is one from no head.
 func catalogueMerge(commit, module string, made time.Time) link.SourceMoved {
-	return link.SourceMoved{Owner: "novox", Repo: "mesh-catalog", Base: "main", Commit: commit,
+	return link.SourceMoved{Owner: "novox", Repo: "mesh-catalog", Base: "main", Head: "pr/" + commit, Commit: commit,
 		MergedAt: made.Format(time.RFC3339Nano), Paths: []string{"modules/" + module + "/module.json"},
 		ModuleDirs: []string{"modules/" + module}, ModuleDirsSaid: true}
 }
 
-// repoMerge is a merge of a repository of one module's own.
+// repoMerge is a merge of a repository of one module's own, from a head branch of its own (catalogueMerge).
 func repoMerge(repo, commit string, made time.Time) link.SourceMoved {
-	return link.SourceMoved{Owner: "novox", Repo: repo, Base: "main", Commit: commit,
+	return link.SourceMoved{Owner: "novox", Repo: repo, Base: "main", Head: "pr/" + commit, Commit: commit,
 		MergedAt: made.Format(time.RFC3339Nano), Paths: []string{"main.go"}}
 }
 
+// fromHead is a merge from a head branch a test names: merges from one head are members of one delivery group,
+// related by it (novox/hq ADR 0304 decision 1), so they share a batch whatever else they share.
+func fromHead(m link.SourceMoved, head string) link.SourceMoved {
+	m.Head = head
+	return m
+}
+
+// lone is a merge that names no head: known to be no delivery group's, it waits for no window unless it is
+// related to a batch assembling (ADR 0304 decision 1).
+func lone(m link.SourceMoved) link.SourceMoved {
+	m.Head = ""
+	return m
+}
+
 // hear is a merge heard at a moment.
 func hear(t *testing.T, open *stores, m link.SourceMoved, now time.Time) {
 	t.Helper()
@@ -154,7 +171,7 @@ func TestThreeRepositoriesInOneWindowAreOneWalk(t *testing.T) {
 	open := windowed(t)
 	asksRecorded(t)
 	for i, r := range []string{"one", "two", "three"} {
-		hear(t, open, repoMerge(r, "c-"+r, t0.Add(time.Duration(i)*20*time.Second)),
+		hear(t, open, fromHead(repoMerge(r, "c-"+r, t0.Add(time.Duration(i)*20*time.Second)), "feat/three"),
 			t0.Add(time.Duration(i)*20*time.Second+time.Second))
 	}
 	cutAt(t, open, t0.Add(41*time.Second+90*time.Second))
@@ -188,8 +205,8 @@ func TestThreeRepositoriesInOneWindowAreOneWalk(t *testing.T) {
 func TestAMergeRestartsTheWindowAndTheMaximumClosesIt(t *testing.T) {
 	open := windowed(t)
 	asksWithPaths(t)
-	hear(t, open, repoMerge("one", "c1", t0), t0)
-	hear(t, open, repoMerge("two", "c2", t0.Add(80*time.Second)), t0.Add(80*time.Second))
+	hear(t, open, fromHead(repoMerge("one", "c1", t0), "feat/both"), t0)
+	hear(t, open, fromHead(repoMerge("two", "c2", t0.Add(80*time.Second)), "feat/both"), t0.Add(80*time.Second))
 	cutAt(t, open, t0.Add(100*time.Second))
 	if ws, _ := walks(t, open); len(ws) != 0 {
 		t.Fatal("the window closed 90 seconds after its first merge, not after its last")
@@ -205,7 +222,7 @@ func TestAMergeRestartsTheWindowAndTheMaximumClosesIt(t *testing.T) {
 	for i := 0; i < 12; i++ {
 		last = t0.Add(time.Duration(i) * time.Minute)
 		repo := []string{"one", "two", "three"}[i%3]
-		hear(t, busy, repoMerge(repo, "c"+string(rune('a'+i)), last), last)
+		hear(t, busy, fromHead(repoMerge(repo, "c"+string(rune('a'+i)), last), "feat/busy"), last)
 		if ws, _ := walks(t, busy); len(ws) > 0 {
 			if i != 10 {
 				t.Fatalf("a busy window closed at merge %d (minute %d), not at its maximum", i, i)
@@ -235,7 +252,7 @@ func TestTheAssemblingBatchIsShown(t *testing.T) {
 	dunst.Number, dunst.Title = 175, "dunst: the font the operator chose"
 	hear(t, open, claude, now.Add(-19*time.Second))
 	hear(t, open, dunst, now.Add(-time.Second))
-	hear(t, open, repoMerge("one", "a6bc0931one", now), now)
+	hear(t, open, fromHead(repoMerge("one", "a6bc0931one", now), dunst.Head), now)
 	out := captured(t, func() error { return plansCommand(t.Context(), nil) })
 	lines := strings.Split(out, "\n")
 	first := lines[0]
@@ -497,8 +514,8 @@ func TestAGroupsOrderBecomesTiersInsideTheWalk(t *testing.T) {
 func TestABatchSurvivesARestart(t *testing.T) {
 	open := windowed(t)
 	asksWithPaths(t)
-	hear(t, open, repoMerge("one", "c1", t0), t0)
-	hear(t, open, repoMerge("two", "c2", t0.Add(30*time.Second)), t0.Add(30*time.Second))
+	hear(t, open, fromHead(repoMerge("one", "c1", t0), "feat/both"), t0)
+	hear(t, open, fromHead(repoMerge("two", "c2", t0.Add(30*time.Second)), "feat/both"), t0.Add(30*time.Second))
 
 	// A new controller: nothing of the first one's but the store.
 	again, err := openStores(t.Context())
@@ -506,7 +523,7 @@ func TestABatchSurvivesARestart(t *testing.T) {
 		t.Fatal(err)
 	}
 	t.Cleanup(again.Close)
-	hear(t, again, repoMerge("one", "c1", t0), t0.Add(60*time.Second)) // the bus hands it over again
+	hear(t, again, fromHead(repoMerge("one", "c1", t0), "feat/both"), t0.Add(60*time.Second)) // the bus hands it over again
 	cutAt(t, again, t0.Add(119*time.Second))
 	if ws, bs := walks(t, again); len(ws) != 0 || len(bs) != 1 || len(bs[0].Delivery.Merges) != 2 {
 		t.Fatalf("the restarted controller's batch: %d walk(s), %+v", len(ws), bs)