Support pub upgrade --dry-run

[timolehto]

The issue has mostly been resolved on the dart side already and it actually supports the --dry-run option dart-lang/sdk#15243. However, flutter does not. So in a dart project one can run:

pub upgrade --dry-run

But with a flutter project you can't do that. If you try using the pub command from dart sdk, you get this error:

Resolving dependencies...
Because card_communicator depends on flutter_test any from sdk which doesn't exist (the Flutter SDK is not available), version
  solving failed.

Flutter users should run `flutter pub get` instead of `pub get`.

And on the other hand:

$ flutter pub upgrade --dry-run
Could not find an option named "dry-run".


Run 'flutter -h' (or 'flutter <command> -h') for available flutter commands and options.

So, yeah would be super nice to get this feature also available for flutter side. @munificent you were heavily involved with the dart side of things. Maybe you know how this could be made to work for flutter? It sounds like the heavy lifting for this has already been done and supporting this on flutter side might be almost trivial?

[munificent]

It should be doable as far as I know, but I don't know much about flutter pub.

[jonahwilliams]

Interestingly flutter pub pub upgrade --dry-run works fine

[mit-mit]

@jonahwilliams this is a general problem with all flags on pub commands. It looks like the overall Flutter flags parser errors out if you try to pass flags, even though the pub command implementation tries to just pass them onto to pub.