False-negative for `ambiguous_import`

[FMorschel]

While working on https://dart-review.googlesource.com/c/sdk/+/386020 I got the following (I'll post the relevant files):

• lib.dart

class Random {}

• root.dart

import 'dart:math'; // To test if this was never used
part 'level1_other.dart';
part 'level1.dart';

• level1.dart

part of 'root.dart';
import 'dart:math';
import 'lib.dart';
part 'level2_other.dart';
part 'test.dart';

• test.dart

part of 'level1.dart';
part 'level3_other.dart';

Random? r;

I was expecting the last line (Random? r;) to give out an ambiguous_import.

Tested with simply the following and it shows the same as above:

import 'dart:math'; // <-- unused_import
import 'lib.dart';

Random? r;

If I comment the import 'lib.dart'; line, nothing goes wrong.

[FMorschel]

Found #58326