haohuaijin opened a new issue, #23083:
URL: https://github.com/apache/datafusion/issues/23083
### Describe the bug
`HashJoinExec.projection: Option<Vec<usize>>` (and the same field on
`NestedLoopJoinExec`) is serialized as a bare `repeated uint32`. Proto3 cannot
tell `None` from `Some(vec![])`, and the decoder treats empty as `None`:
```rust
let projection = if !hashjoin.projection.is_empty() {
Some(hashjoin.projection.iter().map(|i| *i as usize).collect())
} else {
None // Some(vec![]) folded in here
};
```
`Some(vec![])` means "emit zero columns"; `None` means "emit the full join
schema". The round-trip silently changes the output schema. `FilterExec`
already has a workaround for the same proto3 limitation — these two execs were
missed.
### To Reproduce
_No response_
### Expected behavior
_No response_
### Additional context
_No response_
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