[BUG] `Detect Breaking Changes` check does not fail on new method added to an @PublicApi interface

[sachinpkale]

Describe the bug

• Today, Detect Breaking Changes runs on each PR build to avoid introducing any breaking changes to 2.x branch.
• But it does not detect breaking change to a public interface where a new method is added.
• Example: https://github.com/opensearch-project/OpenSearch/pull/15569/files#diff-15dd2c1859d8b3091b1b702af9c5bbdd680224671444870daf9f392d4e838fa1R194

Related component

Build

To Reproduce

• Add a method to any public interface.
  • It is possible that the bug exists only if the new method is overloaded method of existing method.
• Raise PR against 2.x branch.
• Detect Breaking Changes will not fail.

Expected behavior

• For any new method introduced in a public interface, Detect Breaking Changes should fail unless a default implementation is provided.

[reta]

Thanks @sachinpkale for bringing it up, I believe the API check does binary compatible changes at the moment: adding a new method to the interface is binary compatible change. We may need to make the check more strict by enforcing source compatibility.

[dblock]

[Catch All Triage - 1, 2]