pkg/analyzer/lib/src/macro/api/code.dart

// Copyright (c) 2021, the Dart project authors. Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

/// Combines [parts] into a [String].
/// Must only contain [Code] or [String] instances.
String _combineParts(List<Object> parts) {
  var buffer = StringBuffer();

  void write(Object part) {
    if (part is String) {
      buffer.write(part);
    } else if (part is Code) {
      buffer.write(part.code);
    } else if (part is Iterable<Object>) {
      part.forEach(write);
    } else {
      throw UnsupportedError(
        'Only String, Code, and List(s) of them are '
        'allowed but got ${part.runtimeType}',
      );
    }
  }

  write(parts);
  return buffer.toString();
}

/// The representation of a piece of code.
abstract class Code {
  String get code;

  @override
  String toString() => code;
}

/// A piece of code representing a syntactically valid declaration.
class Declaration extends Code {
  @override
  final String code;

  Declaration(this.code);

  /// Creates a [Declaration] from [parts], which must be of type [Code],
  /// [String], or [Iterable]s of them.
  factory Declaration.fromParts(List<Object> parts) =>
      Declaration(_combineParts(parts));
}

/// A piece of code that can't be parsed into a valid language construct in its
/// current form. No validation or parsing is performed.
class Fragment extends Code {
  @override
  final String code;

  Fragment(this.code);

  /// Creates a [Fragment] from [parts], which must be of type [Code],
  /// [String], or [Iterable]s of them.
  factory Fragment.fromParts(List<Object> parts) =>
      Fragment(_combineParts(parts));
}