An apply leaves the resources its scope keeps as they run, so the bus server is not replaced by an unwarranted want (ADR 0594 §2)

internal/apply/module_scope_test.go

@@ -2,6 +2,8 @@ package apply
 
 import (
 	"context"
+	"fmt"
+	"os"
 	"path/filepath"
 	"strings"
 	"testing"
@@ -219,6 +221,82 @@ func TestAResourceThatMovedToItsModulesCompositionIsLeftByTheNodesOwnApply(t *te
 			}
 		})
 	}
+	// Issue 774, ADR 0594 §2: the bus module's first own apply takes over the server the node's own composition made
+	// while the bus was folded. Kept (a want without the warrant's mark), the server's container and its program archive
+	// are left as they run, whatever the build changed in them, and become nats's; its files and the tools' account file
+	// are written. Not kept, the same apply replaces the container.
+	for _, keep := range []bool{true, false} {
+		t.Run(fmt.Sprintf("the bus server kept %v", keep), func(t *testing.T) {
+			dir := t.TempDir()
+			conf, account, program := filepath.Join(dir, "nats.conf"), filepath.Join(dir, "tools", "account"), filepath.Join(dir, "program")
+			bus := func(env, confBody, programBody, module string) *declaration.Declaration {
+				archive, _ := archiveDecl(t, "nats.program-snapshot", program, map[string]string{"snapshot": programBody}, "")
+				if module != "" {
+					archive = strings.Replace(archive, `"id":"nats.program-snapshot"`, `"id":"nats.program-snapshot","module":"nats"`, 1)
+					module = `,"module":"nats"`
+				}
+				return declare(t, archive+`,
+				  {"id":"nats.server-conf","type":"file","path":"`+conf+`","content":"`+confBody+`"`+module+`},
+				  {"id":"nats.server","type":"container","name":"mesh-broker-nats","image":"`+pinned+`","env":{"V":"`+env+
+					`"},"restart-on":["nats.program-snapshot","nats.server-conf"]`+module+`}`)
+			}
+			m := &machine{containers: map[string]*fakeContainer{}}
+			_, state, err := ApplyModule(context.Background(), archHost(t), bus("1", "a", "one", ""), Scope{Module: store.NodeModule},
+				state0(), store.OriginDeclared, m.run, nil, nil, nil, nil)
+			if err != nil {
+				t.Fatal(err)
+			}
+			made := m.containers["mesh-broker-nats"]
+			if made == nil {
+				t.Fatalf("the node's own made no server: %v", m.asked)
+			}
+			m.asked = nil
+			next := bus("2", "b", "two", "nats")
+			next.Resources = append(next.Resources, declare(t, `{"id":"nats.tools-account","type":"file","path":"`+account+
+				`","content":"tools","module":"nats"}`).Resources...)
+			scope := Scope{Module: "nats", Placed: map[string]bool{"nats": true}}
+			if keep {
+				scope.Keep = map[string]bool{"nats.server": true, "nats.program-snapshot": true}
+			}
+			report, after, err := ApplyModule(context.Background(), archHost(t), next, scope, state,
+				store.OriginDeclared, m.run, nil, nil, nil, nil)
+			if err != nil {
+				t.Fatal(err)
+			}
+			var moved []string
+			for _, a := range m.asked {
+				for _, verb := range []string{"docker rm", "docker run", "docker create", "docker stop", "docker restart"} {
+					if strings.HasPrefix(a, verb+" ") {
+						moved = append(moved, a)
+					}
+				}
+			}
+			if keep == (len(moved) > 0) {
+				t.Fatalf("kept %v, and the server was moved by %v", keep, moved)
+			}
+			if got, _ := os.ReadFile(conf); string(got) != "b" {
+				t.Errorf("the server's file holds %q", got)
+			}
+			if got, _ := os.ReadFile(account); string(got) != "tools" {
+				t.Errorf("the tools' account file holds %q", got)
+			}
+			if got, _ := os.ReadFile(filepath.Join(program, "snapshot")); keep != (string(got) == "one") {
+				t.Errorf("kept %v, and the server's program is %q", keep, got)
+			}
+			for _, id := range []string{"nats.server", "nats.program-snapshot"} {
+				rec, ok := after.Find(id)
+				if !ok || rec.Module != "nats" {
+					t.Errorf("%s is recorded %+v, not as nats's", id, rec)
+				}
+				if o := outcomeOf(report, id); keep != (o.Action == keptAsItRuns) {
+					t.Errorf("kept %v, and %s was %s: %s", keep, id, o.Action, o.Detail)
+				}
+			}
+			if keep && report.Changed() == false {
+				t.Error("an apply that wrote the server's files says nothing changed")
+			}
+		})
+	}
 }
 
 func state0() store.State { return store.State{} }