Plugin stopped automatically switching from json to json_lines codec

[newtonne]

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• Version: logstash 7.4.1
• Operating System: Red Hat Enterprise Linux 7.6
• Steps to Reproduce:

1. Start the following pipeline in logstash 6.8.3:

input {
  tcp {
    port    => 10525
    codec => "json"
  }
}
output {
  stdout {}
}

2. In the logs, there will be a message similar to:

[2019-10-30T14:45:38,638][INFO ][logstash.inputs.tcp ] Automatically switching from json to json_lines codec {:plugin=>"tcp"}

3. Start the same pipeline in 7.4.1, there will be no such message since this automatic switching no longer seems to be happening.

I couldn't find this documented as a breaking change anywhere, but I believe it ought to be.