Dart Analyzer goes into an infinite loop if file contains `Stream<List<>>`

[alexander-doroshko]

Reproducible with Dart SDK 2.8.4 and 2.9.0-13.0.dev. Create file foo.dart with the following content

Stream<List<>>

and run dartanalyzer foo.dart. Dart Analyzer runs some infinite calculations which never end.

The same with Dart Analysis Server, so to reproduce just type Stream<List<>> in an empty file in any IDE.

[devoncarew]

cc @scheglov

[scheglov]

When we parse this file, the parser invokes endTypeVariables with invalid endToken. It should be >, but it is EOF.

When I tried to reproduce this in a unit test, the assert was triggered, and we end up with an empty unit, as a safeguard against exceptions in the parser. Maybe assert is not enough and we should check tokens always.

Anyway, I think this is a bug in the parser.

[bwilkerson]

@jensjoha