We'd like to properly support cases like:
```
a.dart:
import 'b.dart';
class A extends B {}
class C {}
b.dart:
import 'a.dart'
class B extends C {}
```
Here both A and B will request a reference to the other during
linking.
We break the cycle by storing libraries in the map after they are
initialized, but before we recursively link them. Now an access to a
library proxy has different guarantees:
* during linking, it guarantees to return an intialized library.
* during program execution, it guarantees to return a linked
library.
Aside from this change, this CL does a minor change to the logic on
`hotReloadEnd` to not change the state of the `libraries` array on a
hot-reload. This change is technically not necessary, but may help us
more clearly track the invariants of the library map: the new logic
keeps updates to the map monotonic over time.
Change-Id: Id2aafa3d94c6bff32b7ddb326f883f978bff6bf0
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/385324
Commit-Queue: Sigmund Cherem <sigmund@google.com>
Reviewed-by: Nicholas Shahan <nshahan@google.com>
Sigmund Cherem
00b11411d6