A grant says whether it names a module's accounts on a node, for the assigner and the compose verb (ADR 0546)

go/delivery/assigner_test.go

@@ -298,4 +298,20 @@ func TestControllerGrant(t *testing.T) {
 	if _, err := EncodeControllerGrant(ControllerGrant{Accounts: []string{""}}); err == nil {
 		t.Errorf("a grant naming an empty account was accepted")
 	}
+	g := ControllerGrant{Accounts: []string{"ace.mesh-build-go", "shanks.mesh-mail.reader"}}
+	for _, c := range []struct {
+		g            ControllerGrant
+		node, module string
+		names        bool
+	}{
+		{g, "ace", "mesh-build-go", true},
+		{g, "shanks", "mesh-mail", true},
+		{g, "g14", "mesh-build-go", false},
+		{g, "ace", "mesh-build", false},
+		{ControllerGrant{}, "novox", "nats", true},
+	} {
+		if got := c.g.NamesNode(c.node, c.module); got != c.names {
+			t.Errorf("%v names %s.%s: %v, want %v", c.g.Accounts, c.node, c.module, got, c.names)
+		}
+	}
 }

go/delivery/grants.go

@@ -73,3 +73,20 @@ func DecodeControllerGrant(data []byte) (ControllerGrant, error) {
 
 // SameControllerGrant says whether two grants are the same value.
 func SameControllerGrant(a, b ControllerGrant) bool { return reflect.DeepEqual(a, b) }
+
+// NamesNode says whether the grant names module's accounts on node: its own `<node>.<module>` or a process's
+// `<node>.<module>.<process>`. A grant that names no account (a module that does not speak on the bus) names every
+// node. The assigner wants a node only once the grant names its account (issue 1945), and the controller's compose
+// verb answers it (ADR 0546 clause 4).
+func (g ControllerGrant) NamesNode(node, module string) bool {
+	if len(g.Accounts) == 0 {
+		return true
+	}
+	own := node + "." + module
+	for _, a := range g.Accounts {
+		if a == own || strings.HasPrefix(a, own+".") {
+			return true
+		}
+	}
+	return false
+}