pub outdated: added clear message for null safe packages

[tusharojha]

Description

The pub outdated --mode=null-safety command gives confusing comments for packages that are already null safe. I have added a message i.e. All dependencies opt in to null-safety. in a case when there are no dependencies shown inside the table.

Fixes #2745

@sigurdm PTAL and suggest changes if any.

[sigurdm]

This will also need some testing.

Look in test/outdated/outdated_test.dart and see if you can make a test-case that prints this.

[tusharojha]

I have added the message to mode please review it!

Also, for adding a unit test I tried creating a test case as follows:

 test('null-safety already migrated', () async {
    await servePackages((builder) => builder
      ..serve('foo', '1.0.0', pubspec: {
        'environment': {'sdk': '>=2.9.0 < 3.0.0'}
      })
      ..serve('foo', '2.0.0', deps: {
        'bar': '2.0.0'
      }, pubspec: {
        'environment': {'sdk': '>=2.12.0 < 3.0.0'}
      })
      ..serve('bar', '1.0.0', pubspec: {
        'environment': {'sdk': '>=2.9.0 < 3.0.0'}
      })
      ..serve('bar', '2.0.0', deps: {
        'foo': '2.0.0'
      }, pubspec: {
        'environment': {'sdk': '>=2.12.0 < 3.0.0'}
      }));

    await d.dir(appPath, [
      d.pubspec({
        'name': 'app',
        'version': '1.0.0',
        'dependencies': {
          'foo': '^2.0.0',
          'bar': '^2.0.0',
        },
        'environment': {'sdk': '>=2.12.0 < 3.0.0'},
      }),
    ]).create();

    await pubGet(environment: {'_PUB_TEST_SDK_VERSION': '2.13.0'});

    await variations('null_safety_already_migrated',
        environment: {'_PUB_TEST_SDK_VERSION': '2.13.0'});
  });

But I am facing a problem in creating the golden file for it! Can you please guide me on how to create a golden file for the same?

[sigurdm]

Yes - you should be able to create the golden file by running the test. If the golden file doesn't exist it will be created. If it exists the actual value will be compared with the file.

[tusharojha]

@sigurdm I have added the test case. Kindle review, and suggest changes if any.

[sigurdm]

LGTM

[sigurdm]

Big thanks for the contribution!