Hold what a walk's merges change on a machine it sends nothing to, and name only where it sent (ADR 0505 §2)

modules/messenger/cmd/messenger/adr505_test.go

@@ -89,3 +89,33 @@ func TestTheControllersOwnConditionsAreNotHeldByAWalkOfAnotherModule(t *testing.
 		}
 	}
 }
+
+// shanksDeclared is a touch as the controller says a machine whose declaration the walk's merges change and to which
+// it sends nothing (mesh-controller walk_said.go walkTouch, `declared`, ADR 0505 §2b).
+var shanksDeclared = Touch{Machine: "shanks", Modules: []string{"mesh-build-image"}, Declared: true}
+
+// ADR 0505 §2b: a machine whose declaration a walk's merges change is held like a machine it sends to, and is not
+// named among the machines the walk reached.
+func TestAMachineWhoseDeclarationTheWalkChangesIsHeldAndNotNamedAsReached(t *testing.T) {
+	ev, ok, err := DecodeWalk([]byte(`{"id":"plan-d","walk":"plan-d","phase":"started","budget_class":"leaf",` +
+		`"bound_seconds":600,"touches":[{"machine":"novox","modules":["gitea"]},` +
+		`{"machine":"shanks","modules":["mesh-build-image"],"declared":true}]}`))
+	if err != nil || !ok || len(ev.Touches) != 2 || !ev.Touches[1].Declared || ev.Touches[0].Declared {
+		t.Fatalf("a declared touch was not read: %+v %v %v", ev.Touches, ok, err)
+	}
+	h, tg, dt, c, _ := newHolder(t)
+	walk(t, h, "plan-d", WalkStarted, "", c.now(), 600, novox("gitea"), shanksDeclared)
+	k := cond("machine.shanks.uncomposable", Urgent, "shanks cannot get new instructions")
+	k.Machine, k.Raised = "shanks", c.now()
+	h.Condition(EventRaised, k)
+	runFor(h, c, time.Minute)
+	if !has(outcomes(h, k.Key), "held") || heard(headlineOf(k.Key), tg, dt) {
+		t.Fatalf("a condition on the declared machine was not held: %v", outcomes(h, k.Key))
+	}
+	if got := touchWords(mergeTouches([]Touch{novox("gitea"), shanksDeclared}, nil)); got != "gitea on novox" {
+		t.Fatalf("what the walk reached reads %q, want only novox", got)
+	}
+	if got := mergeTouches([]Touch{shanksDeclared}, []Touch{{Machine: "shanks", Modules: []string{"buildah"}}}); got[0].Declared {
+		t.Fatalf("a machine the walk also sends to stayed declared: %+v", got)
+	}
+}

modules/messenger/cmd/messenger/walks.go

@@ -94,6 +94,10 @@ func (h *Holder) settle() time.Duration {
 type Touch struct {
 	Machine string   `json:"machine"`
 	Modules []string `json:"modules"`
+	// Declared: the walk sends nothing to this machine, but its merges change the machine's declaration (an
+	// assignment, a provision or a requirement added or removed, ADR 0505 §2b). Held like any touch; never named
+	// among the machines the walk reached.
+	Declared bool `json:"declared,omitempty"`
 }
 
 // WalkEvent is a walk's start or end as the controller says it.
@@ -229,9 +233,10 @@ func DecodeWalk(body []byte) (WalkEvent, bool, error) {
 	}
 	if v, ok := raw["touches"]; ok && string(v) != "null" {
 		var list []struct {
-			Machine string   `json:"machine"`
-			Node    string   `json:"node"`
-			Modules []string `json:"modules"`
+			Machine  string   `json:"machine"`
+			Node     string   `json:"node"`
+			Modules  []string `json:"modules"`
+			Declared bool     `json:"declared"`
 		}
 		if json.Unmarshal(v, &list) != nil {
 			return WalkEvent{}, false, fmt.Errorf("walk %s: touches is not a list of {machine, modules}", ev.Walk)
@@ -242,7 +247,7 @@ func DecodeWalk(body []byte) (WalkEvent, bool, error) {
 				m = t.Node
 			}
 			if m != "" {
-				ev.Touches = append(ev.Touches, Touch{Machine: m, Modules: t.Modules})
+				ev.Touches = append(ev.Touches, Touch{Machine: m, Modules: t.Modules, Declared: t.Declared})
 			}
 		}
 	}
@@ -266,9 +271,11 @@ func DecodeWalk(body []byte) (WalkEvent, bool, error) {
 	return ev, true, nil
 }
 
-// mergeTouches is what two sayings of a walk's touches name together.
+// mergeTouches is what two sayings of a walk's touches name together. A machine is declared only while no saying
+// sends to it (ADR 0505 §2b).
 func mergeTouches(a, b []Touch) []Touch {
 	by := map[string]map[string]bool{}
+	sent := map[string]bool{}
 	var order []string
 	for _, list := range [][]Touch{a, b} {
 		for _, t := range list {
@@ -279,6 +286,9 @@ func mergeTouches(a, b []Touch) []Touch {
 			for _, m := range t.Modules {
 				by[t.Machine][m] = true
 			}
+			if !t.Declared {
+				sent[t.Machine] = true
+			}
 		}
 	}
 	sort.Strings(order)
@@ -289,7 +299,7 @@ func mergeTouches(a, b []Touch) []Touch {
 			mods = append(mods, m)
 		}
 		sort.Strings(mods)
-		out = append(out, Touch{Machine: machine, Modules: mods})
+		out = append(out, Touch{Machine: machine, Modules: mods, Declared: !sent[machine]})
 	}
 	return out
 }
@@ -684,6 +694,9 @@ func touchWords(touches []Touch) string {
 	mods := map[string]bool{}
 	var machines []string
 	for _, t := range touches {
+		if t.Declared {
+			continue // its declaration changed; nothing was sent to it (ADR 0505 §2b)
+		}
 		machines = append(machines, t.Machine)
 		for _, m := range t.Modules {
 			mods[m] = true