End a stranded stop whose modules no merge can carry, so stalled stops listing it (issue 1581)

A stop for a walk that built none of its modules waited for a later merge to
carry them for ever when the pull request removed the module or its plan sent
it nowhere. It now reads ended, as covered reads covered, and leaves stalled.

modules/mesh-delivery-gate/cmd/mesh-delivery-gate/holder.go

@@ -1430,7 +1430,7 @@ func (h *Holder) plan() []func() {
 			h.tellCovered(d, now) // covered before this holder told it, or before a restart (novox/hq issue 480)
 			continue
 		}
-		if strandedUncovered(d) {
+		if strandedOpen(d) {
 			// Stopped and final, but still read for a later merge that delivered its modules: until one did,
 			// `stalled` keeps listing it (review of novox/hq issue 474).
 			var ask []string
@@ -1606,6 +1606,12 @@ func (h *Holder) tellCovered(d *Delivery, now time.Time) {
 // merged change that never reached the machines, which `stalled` keeps listing until a later delivered merge
 // carries its modules (review of novox/hq issue 474).
 func strandedUncovered(d *Delivery) bool {
+	return strandedOpen(d) && !d.strandedEnded()
+}
+
+// strandedOpen is a stop for a walk that built none of its modules that no merge was found to cover: still read for
+// a cover, and listed unless it is ended (novox/hq issue 1581).
+func strandedOpen(d *Delivery) bool {
 	return d.State == Stopped && d.Stranded != "" && d.CoveredBy == ""
 }
 

modules/mesh-delivery-gate/cmd/mesh-delivery-gate/issue1581_test.go

@@ -0,0 +1,72 @@
+package main
+
+import (
+	"strings"
+	"testing"
+	"time"
+)
+
+// novox/hq issue 1581: a delivery stopped because its walk ended without building its modules (issue 474) waited for
+// "a later delivered merge to carry" them, listed by `stalled` for good. When no later merge can: the pull request
+// removed the module from the catalogue (mesh-catalog #384, scan), or the module is built for no machine (#391, "sent
+// nowhere"), the stop reads ended, as covered reads covered (issue 480) — a reading of the stop, no transition — says
+// why, and leaves `stalled`, so the condition that listed it ends by itself.
+
+func strandedWith(t *testing.T, change func(d *Delivery)) (*world, string) {
+	w, id := strandedNight(t)
+	if len(w.h.Stalled()) != 1 {
+		t.Fatalf("before, stalled lists %+v", w.h.Stalled())
+	}
+	w.h.mu.Lock()
+	d := w.h.deliveries[id]
+	change(d)
+	if err := w.store.PutDelivery(d); err != nil {
+		t.Fatal(err)
+	}
+	w.h.mu.Unlock()
+	w.later(time.Minute)
+	w.settleAll()
+	return w, id
+}
+
+func TestAStrandedStopWhoseModuleIsSentNowhereEndsWithoutALaterMerge(t *testing.T) {
+	w, id := strandedWith(t, func(d *Delivery) {
+		d.Plan.Summary = "builds build-agent, sent nowhere; no bus step"
+	})
+	if s := w.h.Stalled(); len(s) != 0 {
+		t.Fatalf("sent nowhere, stalled still lists %+v", s)
+	}
+	shown, err := w.h.Show(id)
+	if err != nil {
+		t.Fatal(err)
+	}
+	reads, _ := shown.(map[string]any)["reads"].(string)
+	if !strings.HasPrefix(reads, "ended") || !strings.Contains(reads, "build-agent") {
+		t.Fatalf("show reads %q", reads)
+	}
+	if waits, _ := shown.(map[string]any)["waits"].(string); strings.Contains(waits, "later delivered merge") {
+		t.Fatalf("it still waits for %q", waits)
+	}
+	if d := w.delivery(id); d.State != Stopped {
+		t.Fatalf("a reading, not a transition: it is %s", d.State)
+	}
+}
+
+func TestAStrandedStopWhoseModuleThePullRequestRemovedEndsWithoutALaterMerge(t *testing.T) {
+	w, _ := strandedWith(t, func(d *Delivery) {
+		d.Removed = []string{"modules/build-agent/module.json", "modules/build-agent/cmd/main.go"}
+	})
+	if s := w.h.Stalled(); len(s) != 0 {
+		t.Fatalf("removed, stalled still lists %+v", s)
+	}
+}
+
+// A stop whose module still runs somewhere keeps waiting for a later merge, and stays listed.
+func TestAStrandedStopWhoseModuleCanStillBeCarriedStaysListed(t *testing.T) {
+	w, _ := strandedWith(t, func(d *Delivery) {
+		d.Removed = []string{"modules/other/module.json"}
+	})
+	if s := w.h.Stalled(); len(s) != 1 {
+		t.Fatalf("stalled lists %+v", s)
+	}
+}

modules/mesh-delivery-gate/cmd/mesh-delivery-gate/model.go

@@ -357,6 +357,44 @@ func (d *Delivery) coveredStop() bool {
 	return false
 }
 
+// strandedEnded is whether a stop for a walk that built none of its modules (novox/hq issue 474), found covered by no
+// merge, waits for nothing that can come: every module its walk left unbuilt is one no later merge can carry, because
+// the pull request removed it from the catalogue (its module.json is among the removed paths) or its plan sends it to
+// no machine ("sent nowhere"). It is a reading of the stop, as covered is (issue 480): the state stays stopped, and
+// `stalled` no longer lists it, so the condition that listed it ends by itself (issue 1581).
+func (d *Delivery) strandedEnded() bool {
+	if d.State != Stopped || d.Stranded == "" || d.CoveredBy != "" {
+		return false
+	}
+	missing := d.notMovedBy()
+	for _, m := range missing {
+		if !d.cannotBeCarried(m) {
+			return false
+		}
+	}
+	return len(missing) > 0
+}
+
+// cannotBeCarried is whether no later merge can deliver a module this delivery's plan moved: it was removed, or the
+// plan sends it nowhere.
+func (d *Delivery) cannotBeCarried(module string) bool {
+	if d.Plan == nil {
+		return false
+	}
+	for _, p := range d.Removed {
+		if strings.HasSuffix(p, "/"+module+"/module.json") {
+			return true
+		}
+	}
+	return strings.Contains(d.Plan.Summary, ", sent nowhere") && len(d.Plan.receiving(module)) == 0
+}
+
+// strandedEndedSaid is how an ended stop reads, in `show`.
+func (d *Delivery) strandedEndedSaid() string {
+	return "ended: it waited for a later merge to carry " + strings.Join(d.notMovedBy(), ", ") +
+		", and none can: the module was removed from the catalogue or is built for no machine (novox/hq issue 1581)"
+}
+
 // coveredStopSaid is how a covered stop or failure reads: on the forge's status, in its view and note, and in `show`.
 func (d *Delivery) coveredStopSaid() string {
 	ended := "its stop"

modules/mesh-delivery-gate/cmd/mesh-delivery-gate/verbs.go

@@ -127,6 +127,8 @@ func (h *Holder) Show(id string) (any, error) {
 		out := map[string]any{"delivery": d, "waits": h.waitsFor(d)}
 		if d.coveredStop() {
 			out["reads"] = d.coveredStopSaid() // stopped, and its change reached the machines (novox/hq issue 480)
+		} else if d.strandedEnded() {
+			out["reads"] = d.strandedEndedSaid() // stopped, and nothing can carry what it waited for (issue 1581)
 		}
 		if g := h.groups[d.Group]; g != nil {
 			state, why := GroupState(g, h.membersOf(g))