generate_package_config.dart needs to treat missing sdk lower bounds as 2.7

[leafpetersen]

Per language team discussion (summarized briefly here we are changing the interpretation of a pubspec sdk constraint with a missing lower bound (or in general no sdk constraint at all, though that will become a pub error) to imply a language version of 2.7. I believe that tools/generate_package_config.dart is one of the few tools that reads pubspec.yaml directly, and hence this will need to be changed there.

This is blocker for beta, and will need to be cherry picked if it doesn't make the beta branch cut.

cc @athomas @jonasfj @munificent If it is possible for one of you to do this tomorrow AAR time, that would be great (you might consider combining this and the DEP roll into a single CL that can be cherry-picked). If not @munificent or I will do this tomorrow.

cc @pcsosinski @mit-mit @franklinyow

[jonasfj]

Playing with this we found that .dart_tool/package_config.json has manually modified in:

• d9bb487
• a6faf8f

I think we should fix this separately, and allow language-version overrides in generate_package_config.dart. I suspect we'll be able to get rid of those overrides rather quickly.

In any case, I don't think updating tools/generate_package_config.dart in a beta blocker.
(nor should we cherry pick such change into the beta release as it's unlikely to affect the generated SDK)

[franklinyow]

Remove from Beta Epic because it is not a blocker

[munificent]

Closing this. The package config generator now reports an error if any of the packages in the repo don't have a fully-specified SDK constraint. There's no need to provide a default to handle missing data when we can just maintain our own packages such that the data isn't missing. :)