*: future-proof DropDB (#903)

When adding an index directory, we didn't account for it in DropDB, causing
os.Remove to error with "directory is not empty". This commit simply iterates
over all directory entries in the storage path and renames them, rather than
only renaming a pre-specified subset. Additionally, Remove has been changed to
RemoveAll in DropDB, which handles directories with elements still in them.

db.go

@@ -643,7 +643,7 @@ func (s *ColumnStore) DropDB(name string) error {
 	s.mtx.Lock()
 	defer s.mtx.Unlock()
 	delete(s.dbs, name)
-	return os.Remove(filepath.Join(s.DatabasesDir(), name))
+	return os.RemoveAll(filepath.Join(s.DatabasesDir(), name))
 }
 
 func (db *DB) openWAL(ctx context.Context, opts ...wal.TestingOption) (WAL, error) {
@@ -668,6 +668,8 @@ func (db *DB) openWAL(ctx context.Context, opts ...wal.TestingOption) (WAL, erro
 const (
 	walPath       = "wal"
 	snapshotsPath = "snapshots"
+	indexPath     = "index"
+	trashPath     = "trash"
 )
 
 func (db *DB) walDir() string {
@@ -679,11 +681,11 @@ func (db *DB) snapshotsDir() string {
 }
 
 func (db *DB) trashDir() string {
-	return filepath.Join(db.storagePath, "trash")
+	return filepath.Join(db.storagePath, trashPath)
 }
 
 func (db *DB) indexDir() string {
-	return filepath.Join(db.storagePath, "index")
+	return filepath.Join(db.storagePath, indexPath)
 }
 
 // recover attempts to recover database state from a combination of snapshots and the WAL.
@@ -1319,10 +1321,22 @@ func validateName(name string) bool {
 	return !strings.Contains(name, "/")
 }
 
-// dropStorage removes snapshots and WAL data from the storage directory.
+// dropStorage removes all data from the storage directory, but leaves the empty
+// storage directory.
 func (db *DB) dropStorage() error {
 	trashDir := db.trashDir()
 
+	entries, err := os.ReadDir(db.storagePath)
+	if err != nil {
+		if os.IsNotExist(err) {
+			// Nothing to drop.
+			return nil
+		}
+		return err
+	}
+	// Try to rename all entries as this is O(1) per entry. We want to preserve
+	// the storagePath for future opens of this database. Callers that want to
+	// drop the DB remove storagePath themselves.
 	if moveErr := func() error {
 		if err := os.MkdirAll(trashDir, os.FileMode(0o755)); err != nil {
 			return fmt.Errorf("making trash dir: %w", err)
@@ -1334,23 +1348,23 @@ func (db *DB) dropStorage() error {
 		if err != nil {
 			return err
 		}
-		if err := os.Rename(db.snapshotsDir(), filepath.Join(tmpPath, snapshotsPath)); err != nil && !os.IsNotExist(err) {
-			return err
-		}
-		if err := os.Rename(db.walDir(), filepath.Join(tmpPath, walPath)); err != nil && !os.IsNotExist(err) {
-			return err
+		errs := make([]error, 0, len(entries))
+		for _, e := range entries {
+			if err := os.Rename(filepath.Join(db.storagePath, e.Name()), filepath.Join(tmpPath, e.Name())); err != nil && !os.IsNotExist(err) {
+				errs = append(errs, err)
+			}
 		}
-		return nil
+		return errors.Join(errs...)
 	}(); moveErr != nil {
-		// If we failed to move the wal/snapshots to the trash dir, fall
-		// back to attempting to remove them with RemoveAll.
-		if err := os.RemoveAll(db.snapshotsDir()); err != nil {
-			return fmt.Errorf("%v: %v", moveErr, err)
-		}
-		if err := os.RemoveAll(db.walDir()); err != nil {
-			return fmt.Errorf("%v: %v", moveErr, err)
+		// If we failed to move storage path entries to the trash dir, fall back
+		// to attempting to remove them with RemoveAll.
+		errs := make([]error, 0, len(entries))
+		for _, e := range entries {
+			if err := os.RemoveAll(filepath.Join(db.storagePath, e.Name())); err != nil {
+				errs = append(errs, err)
+			}
 		}
-		return moveErr
+		return errors.Join(errs...)
 	}
 	return os.RemoveAll(trashDir)
 }