Property merging in component template fails on subobjects:false

[flash1293]

Elasticsearch Version

main

Installed Plugins

No response

Java Version

bundled

OS Version

macOS Catalina

Problem Description

When using subobjects: false in a component template and adding a field into the same object via dotted field name, an error is thrown even though valid mappings can be built and are built correctly when using two separate component templates

Steps to Reproduce

PUT _component_template/broken_template
{
  "template": {
    "mappings": {
      "properties": {
        "foo": {
          "type": "object",
          "subobjects": false
        },
        "foo.bar": {
          "type": "keyword"
        }
      }
    }
  }

fails with the [subobjects] parameter can't be updated for the object mapping [foo].

However, defining foo and foo.bar in the exact same way in two component templates works correctly:

PUT _component_template/working_template1
{
  "template": {
    "mappings": {
      "properties": {
        "foo": {
          "type": "object",
          "subobjects": false
        }
      }
    }
  }
}

PUT _component_template/working_template2
{
  "template": {
    "mappings": {
      "properties": {
        "foo.bar": {
          "type": "keyword"
        }
      }
    }
  }
}

PUT _index_template/working_match
{
  "index_patterns": ["mytest"],
  "priority": 1000,
  "composed_of": [
    "working_template1",
    "working_template2"
  ]
}

PUT mytest

GET mytest

After this mytest has the mappings:

    "mappings": {
      "properties": {
        "foo": {
          "subobjects": false,
          "properties": {
            "bar": {
              "type": "keyword"
            }
          }
        }
      }
    }

I would expect the broken_template from above to result in the same mapping instead of failing with an error.

Logs (if relevant)

No response

[flash1293]

My hunch is that

"foo.bar": {
          "type": "keyword"
        }

is implicitly creating foo as an object with implicit subobjects: true, then the actual definition breaks that by switching to subobjects: false. Maybe we can validate afterwards instead?

[elasticsearchmachine]

Pinging @elastic/es-storage-engine (Team:StorageEngine)