internal/apply/apply.go

@@ -601,7 +601,37 @@ func applyService(ctx context.Context, sys system.System, r *declaration.Service
 // installed would be describing an effect it declined to have.
 func remove(ctx context.Context, sys system.System, a store.Applied, run Runner) (string, string, error) {
 	switch declaration.Type(a.Type) {
-	case declaration.TypeFile, declaration.TypeDirectory:
+	case declaration.TypeDirectory:
+		// **A directory with anything left in it is kept, and that is the rule that protects
+		// data.** Everything the mesh put inside is itself a declared resource, and orphans are
+		// removed in reverse declaration order — so by the time a directory comes to be removed,
+		// what the mesh wrote there is already gone. Anything still present is something nobody
+		// declared: a database's files, a mail spool, somebody's uploads.
+		//
+		// Before this, unassigning a module deleted its data directory and everything under it,
+		// and the report said "removed". Nothing anywhere said what had been in there.
+		//
+		// This is the host's own line, applied to the one shape where getting it wrong is not
+		// recoverable: it removes what it made and leaves what it merely configured. An empty
+		// directory is what it made. A full one is not.
+		entries, err := os.ReadDir(a.Target)
+		if errors.Is(err, os.ErrNotExist) {
+			return "forgotten", "no longer there", nil
+		}
+		if err != nil {
+			return "", "", err
+		}
+		if len(entries) > 0 {
+			return "kept", fmt.Sprintf(
+				"no longer declared, and %d item(s) inside that the mesh did not put there — "+
+					"remove it by hand once you know what it is", len(entries)), nil
+		}
+		if err := os.Remove(a.Target); err != nil {
+			return "", "", err
+		}
+		return "removed", "no longer declared, and empty", nil
+
+	case declaration.TypeFile:
 		if err := os.RemoveAll(a.Target); err != nil {
 			return "", "", err
 		}

internal/apply/apply_test.go

@@ -1360,3 +1360,74 @@ func TestResourcesAreAppliedInTheOrderTheyWereDeclared(t *testing.T) {
 			"another has no way to say so", ran)
 	}
 }
+
+// **A data directory is never removed by the mesh.** The one failure in this system that cannot
+// be undone.
+//
+// Unassigning a module made its directory an orphan, and an orphan directory was deleted with
+// everything under it — a database's files, a mail spool, somebody's uploads — and the report
+// said "removed". Reproduced before it was fixed: a module was assigned, a service wrote into
+// its directory, the module was unassigned, and the file was gone.
+//
+// What makes the rule safe rather than merely cautious is the removal order. Everything the mesh
+// puts in a directory is itself a declared resource, and orphans are removed in reverse
+// declaration order — so what the mesh wrote is already gone by the time the directory is
+// reached. Anything still there was put there by something else.
+func TestADirectoryHoldingAnythingTheMeshDidNotPutThereIsKept(t *testing.T) {
+	root := t.TempDir()
+	data := filepath.Join(root, "keycloak")
+
+	d := declare(t, `{"id":"data","type":"directory","path":"`+data+`","mode":"0700"}`)
+	_, state, err := Apply(context.Background(), archHost(t), d, store.State{},
+		store.OriginDeclared, nil, nil, nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+	live := filepath.Join(data, "realm.db")
+	if err := os.WriteFile(live, []byte("everybody's logins"), 0o600); err != nil {
+		t.Fatal(err)
+	}
+
+	// The module is unassigned: the mesh declares something else entirely.
+	after := declare(t, `{"id":"other","type":"directory","path":"`+filepath.Join(root, "other")+`","mode":"0700"}`)
+	report, _, err := Apply(context.Background(), archHost(t), after, state,
+		store.OriginDeclared, nil, nil, nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if _, err := os.Stat(live); err != nil {
+		t.Fatalf("the data was deleted by unassigning a module: %v", err)
+	}
+	// And it is said, rather than left for somebody to notice. A directory quietly left behind is
+	// how a machine accumulates things nobody can account for.
+	var said bool
+	for _, o := range report.Outcomes {
+		if o.Action == "kept" && strings.Contains(o.Detail, "did not put there") {
+			said = true
+		}
+	}
+	if !said {
+		t.Errorf("the directory was kept and nothing reported it: %+v", report.Outcomes)
+	}
+}
+
+// An empty one is the mesh's own, and goes.
+func TestAnEmptyDirectoryIsStillRemoved(t *testing.T) {
+	root := t.TempDir()
+	mine := filepath.Join(root, "config")
+	d := declare(t, `{"id":"c","type":"directory","path":"`+mine+`","mode":"0700"}`)
+	_, state, err := Apply(context.Background(), archHost(t), d, store.State{},
+		store.OriginDeclared, nil, nil, nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+	after := declare(t, `{"id":"other","type":"directory","path":"`+filepath.Join(root, "other")+`","mode":"0700"}`)
+	if _, _, err := Apply(context.Background(), archHost(t), after, state,
+		store.OriginDeclared, nil, nil, nil); err != nil {
+		t.Fatal(err)
+	}
+	if _, err := os.Stat(mine); !errors.Is(err, os.ErrNotExist) {
+		t.Fatal("an empty directory the mesh made was left behind, so nothing is ever cleaned up")
+	}
+}