bigluck opened a new pull request, #25944:
URL: https://github.com/apache/datafusion/pull/25944
## Which issue does this PR close?
- Closes #25937.
## Rationale for this change
The optimizer reduces queries like `SELECT * FROM t LIMIT 0` or `... WHERE
false` to an `EmptyRelation` that keeps the schema of its input, but
`EmptyRelationNode` only stored `produce_one_row`. After a protobuf round trip
the plan came back without columns, and plans where another node refers to
those columns, like `SELECT max(id), count(*) FROM t WHERE false`, failed to
decode.
## What changes are included in this PR?
- Add a `schema` field to `EmptyRelationNode`, encoded and decoded like
`DropViewNode`.
- Fall back to the previous empty schema for older payloads without it.
- Regenerate the prost and pbjson models.
- Add `roundtrip_empty_relation_schema` and update the expected JSON in
`plan_to_json`.
- Document the new generated field in the 56.0.0 upgrade guide.
## Are these changes tested?
Yes:
- `cargo test -p datafusion-proto --features json,avro --test
proto_integration`
- `cargo fmt --all -- --check`
- `cargo clippy -p datafusion-proto -p datafusion-proto-models --all-targets
--all-features -- -D warnings`
- `./dev/rust_lint.sh`
`json_to_plan` still decodes `{"emptyRelation":{}}`, which covers payloads
from older versions.
## Are there any user-facing changes?
Logical plans reduced to an `EmptyRelation` keep their schema across
protobuf round trips. The wire format remains backward compatible; the
generated `EmptyRelationNode` struct gains a `schema` field, documented in the
upgrade guide.
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