Analyzer thinks import of extension operator is unused when it is used.

[joshualitt]

SDK:
Dart SDK version: 3.1.0-edge.fad51247fcd2810955a9a927d5f44618a30cad34 (be) (Thu May 4 17:50:22 2023 +0000) on "linux_x64"

Repro:

// foo.dart:
class Foo {
  Map<String, String> data = {};
}

// ext.dart:
import 'foo.dart';
  
extension FooExt on Foo {
  void operator[]=(String p, String v) => this.data[p] = v;
}

// main.dart
import 'foo.dart';
import 'ext.dart';

void main() {
  final foo = Foo();
  foo['a'] = 'b';
}

dart analyze produces:

warning • main.dart:2:8 • Unused import: 'ext.dart'. Try removing the import directive. •
          unused_import

[scheglov]

https://dart-review.googlesource.com/c/sdk/+/306123