build: print out the number of warnings after completing a rule check

[daghack]

Atm when building with --check, when there are no warnings we generate the output
Check completed, no warnings found.

 => => transferring context: 88B                                                                                                                         0.0s
Check completed, no warnings found.

When there are warnings, we leap right into displaying them.

 => => transferring context: 88B 

WARNING: FromAsCasing - https://docs.docker.com/go/dockerfile/rule/from-as-casing/ ....

This updates the output in the later case to contain a similar "Check completed" message which lists the warning count.

 => => transferring context: 88B 
Check completed, 1 warning found!

WARNING: FromAsCasing - https://docs.docker.com/go/dockerfile/rule/from-as-casing/ ....

[crazy-max]

Can we have an integration test for both running check with and without warning to validate this?

[daghack]

Can we have an integration test for both running check with and without warning to validate this?

Added!

[daghack]

@crazy-max @tonistiigi ping

[tonistiigi]

@daghack Did you check the output of this for buildx bake as well?

[daghack]

@tonistiigi Good catch. Will update!

[crazy-max]

@daghack Did you check the output of this for buildx bake as well?

Yes another integration for bake would be ideal to make sure

[daghack]

@crazy-max @tonistiigi Added matching integration checks for bake! :)