feat: specify flutter version in shorebird.yaml

[alexobviously]

Description

Currently it is only possible to specify a specific flutter version by passing an argument when calling the Shorebird CLI. This works fine, but for big projects, it would be cleaner if we could specify a version in shorebird.yaml, consistent with how we specify dart/flutter verisons in pubspec.yaml etc.

Requirements

• A parameter in shorebird.yaml that allows specifying a flutter version
• Can still be overridden by --flutter-version, I think?

[eseidel]

Certainly fair. Another alternative would be for us to teach shorebird to read the version from fvm or similar.

#1972 might be another approach to avoid needing to specify? But I agree, it would be nice to specify the flutter version in source control somehow, and we should just respect whatever way already exists to do that in the flutter community (e.g. fvm?).

[alexobviously]

I obviously can't speak for everyone and perhaps my experience is not the standard, but in our case, I'd say explicitly specifying in a single file would actually be the optimal solution, so that we get predictable results regardless of who on the team builds the release/patch, and it's easy to maintain that way too. But yeah maybe I am missing a much better workflow with fvm or similar.

btw I would be happy to have a go at adding this myself, just having a look through the shorebird_cli code and it looks pretty comprehensible

[eseidel]

If there is not a way to currently specify flutter version in source, that does seem reasonable that shorebird release should take the flutter version from shorebird.yaml by default. 🤷 Thanks for the suggestion!

[erickzanardo]

pubspec.yaml actually allows you to specify a flutter version, here is an example.

Its is meant to be used mainly on published packages as state in this comment, and it doesn't force you to pin a version, it allows a range, which I am not sure if can bring some confusion.

Either way, I feel it would bring even more confusion if we added yet another version field to shorebird.yaml that does something similar to the one on pubspec.yaml...

So I would suggest that instead of adding a new field to shorebird's config file, we could read the one on pubspec, respect the range (so if the field says >=3.22.0 and shorebird supports 3.22.1, the later will be used), and it can be overridden by the flag.