sources property
A mapping from source URIs to directly reachable source URIs. For example,
a file "foo.dart" that imports "bar.dart" would have the corresponding
mapping { "file:///foo.dart" : "file:///bar.dart"
}. If "bar.dart" has
further imports (or exports) there will be a mapping from the URI
"file:///bar.dart" to them. To check if a specific URI is reachable from a
given file, clients can check for its presence in the resulting key set.
Implementation
final Map<String, List<String>> sources;