A library augmentation can not be an entry point

[eernstg]

See dart-lang/language#3642 for the background discussion.

This issue tracks the implementation of a startup time error which is emitted by the CFE when an execution of a Dart program is requested and the given entry point (the file that "is" the program) is an library augmentation. For example:

// --- Library 'main.dart'.
import augment 'augment.dart';
...
void main() {}

// --- Library augmentation 'augment.dart'.
augment library 'main.dart';
...

With these Dart source files, it is a startup time error to execute the program using a command like dart augment.dart because augment.dart is a library augmentation. However, dart main.dart is fine.

Note that the declaration of the top-level function main could occur in the library or in the library augmentation, and that would not make a difference (the library main.dart will export main in either case, and using augment.dart as an entry point is an error in either case).

[eernstg]

@johnniwinther, could you select a priority for this issue?