Fix Lockfile Schematics

internal/topdata/native.go

@@ -1,6 +1,7 @@
 package topdata
 
 import (
+	"bytes"
 	"encoding/json"
 	"errors"
 	"fmt"
@@ -3600,17 +3601,121 @@ func saveLockfile(path string, lockData map[string]int) error {
 	if err := os.MkdirAll(filepath.Dir(path), 0o755); err != nil {
 		return fmt.Errorf("create lockfile parent: %w", err)
 	}
-	raw, err := json.MarshalIndent(lockData, "", "  ")
+	keys, err := orderedLockfileKeys(path, lockData)
+	if err != nil {
+		return fmt.Errorf("read lockfile order: %w", err)
+	}
+	raw, err := marshalOrderedLockfile(keys, lockData)
 	if err != nil {
 		return fmt.Errorf("marshal lockfile: %w", err)
 	}
-	raw = append(raw, '\n')
 	if err := os.WriteFile(path, raw, 0o644); err != nil {
 		return fmt.Errorf("write lockfile %s: %w", path, err)
 	}
 	return nil
 }
 
+func orderedLockfileKeys(path string, lockData map[string]int) ([]string, error) {
+	existingKeys, err := readLockfileKeyOrder(path)
+	if err != nil && !errors.Is(err, os.ErrNotExist) {
+		return nil, err
+	}
+
+	keys := make([]string, 0, len(lockData))
+	seen := make(map[string]struct{}, len(lockData))
+	for _, key := range existingKeys {
+		if _, ok := lockData[key]; !ok {
+			continue
+		}
+		keys = append(keys, key)
+		seen[key] = struct{}{}
+	}
+
+	extraKeys := make([]string, 0, len(lockData)-len(keys))
+	for key := range lockData {
+		if _, ok := seen[key]; ok {
+			continue
+		}
+		extraKeys = append(extraKeys, key)
+	}
+	slices.Sort(extraKeys)
+	keys = append(keys, extraKeys...)
+	return keys, nil
+}
+
+func readLockfileKeyOrder(path string) ([]string, error) {
+	raw, err := os.ReadFile(path)
+	if err != nil {
+		return nil, err
+	}
+
+	decoder := json.NewDecoder(bytes.NewReader(raw))
+	token, err := decoder.Token()
+	if err != nil {
+		return nil, err
+	}
+	delim, ok := token.(json.Delim)
+	if !ok || delim != '{' {
+		return nil, fmt.Errorf("%s must contain a JSON object", path)
+	}
+
+	keys := []string{}
+	for decoder.More() {
+		token, err := decoder.Token()
+		if err != nil {
+			return nil, err
+		}
+		key, ok := token.(string)
+		if !ok {
+			return nil, fmt.Errorf("%s contains a non-string object key", path)
+		}
+		var value json.RawMessage
+		if err := decoder.Decode(&value); err != nil {
+			return nil, err
+		}
+		keys = append(keys, key)
+	}
+
+	token, err = decoder.Token()
+	if err != nil {
+		return nil, err
+	}
+	delim, ok = token.(json.Delim)
+	if !ok || delim != '}' {
+		return nil, fmt.Errorf("%s must contain a JSON object", path)
+	}
+	return keys, nil
+}
+
+func marshalOrderedLockfile(keys []string, lockData map[string]int) ([]byte, error) {
+	if len(keys) == 0 {
+		return []byte("{}\n"), nil
+	}
+
+	var buffer bytes.Buffer
+	buffer.WriteString("{\n")
+	for index, key := range keys {
+		keyRaw, err := json.Marshal(key)
+		if err != nil {
+			return nil, err
+		}
+		valueRaw, err := json.Marshal(lockData[key])
+		if err != nil {
+			return nil, err
+		}
+		buffer.WriteString("  ")
+		buffer.Write(keyRaw)
+		buffer.WriteString(": ")
+		buffer.Write(valueRaw)
+		if index < len(keys)-1 {
+			buffer.WriteByte(',')
+		}
+		buffer.WriteByte('\n')
+	}
+	buffer.WriteString("}\n")
+	return buffer.Bytes(), nil
+}
+
 func loadLegacyTLK(root string) (*legacyTLKData, error) {
 	info, err := os.Stat(root)
 	if err != nil {

internal/topdata/topdata_test.go

@@ -108,6 +108,29 @@ func TestResolvedTableRegistryRegistersConsistentTables(t *testing.T) {
 	}
 }
 
+func TestSaveLockfilePreservesExistingOrderAndAppendsNewKeys(t *testing.T) {
+	root := t.TempDir()
+	lockPath := filepath.Join(root, "lock.json")
+	writeFile(t, lockPath, "{\n  \"b\": 2,\n  \"a\": 1\n}\n")
+
+	if err := saveLockfile(lockPath, map[string]int{
+		"b": 2,
+		"a": 1,
+		"c": 3,
+	}); err != nil {
+		t.Fatalf("saveLockfile failed: %v", err)
+	}
+
+	got, err := os.ReadFile(lockPath)
+	if err != nil {
+		t.Fatalf("read lockfile: %v", err)
+	}
+	want := "{\n  \"b\": 2,\n  \"a\": 1,\n  \"c\": 3\n}\n"
+	if string(got) != want {
+		t.Fatalf("unexpected lockfile contents:\n%s", string(got))
+	}
+}
+
 func TestResolvedTableRegistryRejectsDuplicateKeys(t *testing.T) {
 	_, err := newResolvedTableRegistry([]nativeCollectedDataset{
 		{