ESQL: unexpected verification_exception for same field name in two indices (union types)

[astefan]

Description

test1 index

{
    "mappings": {
        "properties": {
            "x": {
                "type": "keyword"
            }
        }
    }
}

test2 index

{
    "mappings": {
        "properties": {
            "x": {
                "type": "long"
            },
            "whatever": {
                "type": "text"
            }
        }
    }
}

from test* | rename whatever as foo results in

     "type": "verification_exception",
        "reason": "Found 1 problem\nline 1:1: Cannot use field [x] due to ambiguities being mapped as [2] incompatible types: [keyword] in [test1], [long] in [test2]",
        "stack_trace": "org.elasticsearch.xpack.esql.VerificationException: Found 1 problem\nline 1:1: Cannot use field [x] due to ambiguities being mapped as [2] incompatible types: [keyword] in [test1], [long] in [test2]

[elasticsearchmachine]

Pinging @elastic/es-analytical-engine (Team:Analytics)

[alex-spies]

I can confirm that the given query used to work on 8.14, but breaks on current main and on 8.15.

[alex-spies]

There's a workaround: you can just DROP the offending field before the RENAME.

from test* | drop x | rename whatever as foo