Abstract field support: do not allow initializing abstract fields.

There are three ways to initialize a field, so we have to check for
three error conditions:
- At the declaration site
- Via a field formal parameter
- Via a constructor initializer

Fixes #42981

Change-Id: Ifc32a28ffb62d60fd2171d4980e88da9eebcb481
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/157664
Reviewed-by: Konstantin Shcheglov <scheglov@google.com>
Commit-Queue: Paul Berry <paulberry@google.com>

https://dart.googlesource.com/sdk/+/92315c4b2dc24c13ce681a34992477991dafce48
1 file changed
tree: 86ec6bc3ae71769fbad84e0ebc3479e48d8897e6
  1. commits.json