Index alias on another alias does not retain the initial filter

[athanikkal]

If we create an alias on an index with a filter and then subsequently create another alias on the first alias, the second alias does not retain the original filter.

The steps to reproduce.

// create index
curl -XPOST localhost:9200/test -d '{
    "settings" : {
        "number_of_shards" : 1
    },
    "mappings" : {
        "type1" : {
            "properties" : {
                "field1" : { "type" : "string", "index" : "not_analyzed" }
            }
        }
    }
}'

// create first alias
curl -XPOST 'http://localhost:9200/_aliases' -d '{
    "actions" : [
        {
            "add" : {
                 "index" : "test",
                 "alias" : "alias1",
                 "filter" : { "term" : { "field1" : "kimchy" } }
            }
        }
    ]
}'

// create secons alias
curl -XPOST 'http://localhost:9200/_aliases' -d '{
    "actions" : [
        {
            "add" : {
                 "index" : "alias1",
                 "alias" : "alias2"
            }
        }
    ]
}'

// Retrieve the first alias definition
curl -XGET http://localhost:9200/_alias/alias1?pretty

{
  "test" : {
    "aliases" : {
      "alias1" : {
        "filter" : {
          "term" : {
            "field1" : "kimchy"
          }
        }
      }
    }
  }
}

// Retrieve the second alias definition
curl -XGET http://localhost:9200/_alias/alias2
{
  "test" : {
    "aliases" : {
      "alias2" : { }
    }
  }
}

Please see that there is no filter associated with the second alias.

[javanna]

I think this is more of a documentation issue, which we already have an issue for: #10106 . Alias to alias is not supported and will just create an alias that points to the indices that the target alias points to at creation time. We should document this better so people are not too surprised when this happens. Closing in favor of #10106 .