Hi Yuepeng, Rui, Thanks for the inventory. This is a cleanup I'd like to see too.
One question: does the doc separate withDeprecatedKeys from withFallbackKeys? Only the first sets FallbackKey.isDeprecated, and Configuration#loggingFallback branches on it, so a deprecated key logs WARN while a plain fallback logs INFO. It matters because most withFallbackKeys sites on master (e01bbca) are not old names at all. rest.address falls back to jobmanager.rpc.address, taskmanager.slot.timeout to pekko.ask.timeout, process.*.working-dir to process.working-dir. Those are cross-option defaults, and removing them would change behaviour for users who never set a deprecated key. A few really are old names, just declared as plain fallbacks: s3.access.key, s3.secret.key, s3.path.style.access, web.address behind rest.bind-address, and schema-registry.url / .subject / .schema in avro-confluent. Those never logged a deprecation warning, only an INFO line calling them a supported fallback. Does the "deprecated before 1.20.0" reasoning still cover keys that were never announced as deprecated, or should they be marked deprecated first and removed a release later? I'm a contributor, not a committer, so this is just input. I can help work through the list if that's useful. Best regards, Sai Krishna Sepuri
