When using ConfigStringLoader, a default stdout can be added out of nowhere

[lucabelluccini]

In case someone uses the following config in pipeline.yml:

- pipeline.id: "demo"
  pipeline.ecs_compatibility: disabled
  pipeline.workers: 3
  pipeline.batch.size: 5
  config.string: |
    input {
      generator {
        lines => [
          '{"hello": "world"}'
        ]
        count => 1
      }
    }

    filter
    {
      json {
        source => "message"
        remove_field => [ "message" ]
      }

    output
    {
      file {
        path => "/tmp/somefile.ndjson"
        codec => json_lines
      }
    }

Note the:

output
{
    ...

Then, a default stdout output is added.

This is confusing as this behavior is not documented.

Possible solutions:

1. Make the regex

   logstash/logstash-core/lib/logstash/config/source/local.rb

   Line 36 in 0875e0b

   OUTPUT_BLOCK_RE = /output *{/

   match also newlines or spaces between output and {
2. Log a WARN if the default output is added