Add binary compatibility validator

[twyatt]

Fixes #40.

Use binary-compatibility-validator for validating binary compatibility between releases.

[codecov[bot]]

Codecov Report

Merging #56 into develop will not change coverage. The diff coverage is n/a.

@@            Coverage Diff             @@
##             develop      #56   +/-   ##
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  Coverage      83.23%   83.23%           
  Complexity        57       57           
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  Files             14       14           
  Lines            352      352           
  Branches          34       34           
==========================================
  Hits             293      293           
  Misses            48       48           
  Partials          11       11           

[twyatt]

Are the *.api files autogenerated?

They are generated via ./gradlew apiDump (task provided by binary-compatibility-validator).

After you commit the *.api you can easily make code changes and see how your API changed by re-running ./gradlew apiDump and looking at the diff in git. 😄

./gradlew apiCheck fails if your API differs from the existing *.api files. It's not a feature rich as japicmp in that it will fail for any change, not just incompatible changes. It's up to the maintainer to determine if the change warrants a version bump.

[twyatt]

I especially like this approach as I examine the *.api files and realized that I had some of the logging methods exposed on the public API.

Makes it easy to evaluate how your public API surface looks.