feat: Let pop dismiss flow

[Hackmodford]

Just ran into an issue where I have a page that can be the start of a flow, or pushed as a regular page.

When ran as a flow, context.pop() doesn't work.

Would it make sense for context.pop() to attempt dismissFlow() if popping the first page in a flow?

[Mastersam07]

Yes, that would make sense. This would be somewhere between a bug and a feature request. The system back button on that same screen already does exactly what you're asking for. The flow's PopScope handler is:

if (flow.router.canPop) flow.router.pop(); else completeFlow(null);

So on a flow root, back dismisses the flow but context.pop() returns false and does nothing. Two ways of saying "go back" disagree, and the API is the one that's wrong.

Rather than dismissFlow(), pop(result) should complete the flow with that result. Otherwise your dual-use page still breaks in the other direction; pushed with pushForResult<String> it returns a value, run as a flow it silently returns null.

Completing with the value makes the screen's contract identical in both modes, which is the thing you're actually after.

Until it ships, this should work today:

    void goBack(BuildContext context, [String? result]) {
      if (FlowScope.maybeOf(context) != null) {
        context.completeFlow<String>(result);
      } else {
        context.pop(result);
      }
    }

We would target this in version 1.2.0. Note it may include a change to documented behaviour (pop is specified to return false when it can't pop), so it'll be called out in the changelog rather than slipped in.