resolveDartExecutable function

String resolveDartExecutable({ String? resolvedExecutable, Map<String, String>? environment, bool exists(String path)?, })

The dart executable to use when a tool needs to spawn an SDK command.

SCE51. Platform.resolvedExecutable is the Dart runtime ONLY when the tool runs under dart run. An AOT-compiled tom CLI is its own resolvedExecutable, so spawning Platform.resolvedExecutable analyze ... re-invokes the tool with arguments it does not understand. d4rtgen did exactly that for --verify-output: the child parsed analyze as a positional, generated bridges in the working directory, printed nothing the parent recognised as a diagnostic, and exited 0 — so the parent reported "analysed clean" having analysed nothing. The verification was a silent no-op in every compiled run, and only became visible when the flag was made default-on, at which point the child verified too and it turned into a fork bomb.

Resolution order, first hit wins:

1. resolvedExecutable itself, when it IS the Dart runtime.
2. DART_SDK/bin/dart.
3. FLUTTER_ROOT/bin/cache/dart-sdk/bin/dart.
4. The first dart on PATH.
5. The bare name dart, for the OS to resolve.

The last resort is deliberately a bare name rather than the current executable: a command that cannot be found fails loudly, where one that re-enters the tool does not fail at all.

Implementation

String resolveDartExecutable({
  String? resolvedExecutable,
  Map<String, String>? environment,
  bool Function(String path)? exists,
}) {
  final executable = resolvedExecutable ?? Platform.resolvedExecutable;
  final env = environment ?? Platform.environment;
  final isFile = exists ?? (path) => File(path).existsSync();
  final dartName = Platform.isWindows ? 'dart.exe' : 'dart';

  final name = executable.split(RegExp(r'[/\\]')).last.toLowerCase();
  if (name == 'dart' || name == 'dart.exe') return executable;

  for (final candidate in [
    if (env['DART_SDK'] case final sdk?) '$sdk/bin/$dartName',
    if (env['FLUTTER_ROOT'] case final root?)
      '$root/bin/cache/dart-sdk/bin/$dartName',
  ]) {
    if (isFile(candidate)) return candidate;
  }

  final separator = Platform.isWindows ? ';' : ':';
  for (final entry in (env['PATH'] ?? '').split(separator)) {
    if (entry.isEmpty) continue;
    final candidate = '$entry/$dartName';
    if (isFile(candidate)) return candidate;
  }

  return dartName;
}