[flutter_tools] YamlException "Expected a key while parsing a block mapping" parsing localizations #123148
Description
On beta/3.9.0-1.0.pre.2
With command: flutter gen-l10n
YamlException: Error on line 4, column 26: Expected a key while parsing a block mapping.
╷
4 │ template-arb-file: {name}_en.arb
│ ^
╵
at Parser._parseBlockMappingKey(parser.dart:456)
at Parser._stateMachine(parser.dart:100)
at Parser.parse(parser.dart:61)
at Loader._loadMapping(loader.dart:175)
at Loader._loadNode(loader.dart:92)
at Loader._loadDocument(loader.dart:68)
at Loader.load(loader.dart:60)
at loadYamlDocument(yaml.dart:72)
at loadYamlNode(yaml.dart:57)
at parseLocalizationsOptions(localizations_utils.dart:439)
at GenerateLocalizationsCommand.runCommand(generate_localizations.dart:232)
at FlutterCommand.verifyThenRunCommand(flutter_command.dart:1465)
at <asynchronous gap>(async)
at FlutterCommand.run.<anonymous closure>(flutter_command.dart:1301)
at <asynchronous gap>(async)
at AppContext.run.<anonymous closure>(context.dart:150)
at <asynchronous gap>(async)
at CommandRunner.runCommand(command_runner.dart:212)
at <asynchronous gap>(async)
at FlutterCommandRunner.runCommand.<anonymous closure>(flutter_command_runner.dart:288)
at <asynchronous gap>(async)
at AppContext.run.<anonymous closure>(context.dart:150)
at <asynchronous gap>(async)
at FlutterCommandRunner.runCommand(flutter_command_runner.dart:236)
at <asynchronous gap>(async)
at run.<anonymous closure>.<anonymous closure>(runner.dart:64)
at <asynchronous gap>(async)
at AppContext.run.<anonymous closure>(context.dart:150)
at <asynchronous gap>(async)
at main(executable.dart:91)
at <asynchronous gap>(async)
This actually seems like a reasonably helpful error message, I think the action item here should be ensuring this is toolexit rather and not hitting crash reporting.