zhuqi-lucas opened a new issue, #21229:
URL: https://github.com/apache/datafusion/issues/21229
## Description
When `FilterExec` has a `fetch` value (from limit pushdown), the
`TreeRender` display format does not include it in the output, while
`Default`/`Verbose` formats correctly show `fetch=N`.
This means `EXPLAIN FORMAT TREE` output is incomplete — the limit
information is silently dropped from the FilterExec node.
## Steps to Reproduce
```sql
CREATE TABLE t1 (a INT) AS VALUES (1),(2),(3),(4),(5),(6),(7),(8),(9),(10);
-- Default format shows fetch:
EXPLAIN SELECT a FROM t1 WHERE a > 3 LIMIT 5;
-- FilterExec: a@0 > 3, fetch=5 ✅
-- Tree format does NOT show fetch:
EXPLAIN FORMAT TREE SELECT a FROM t1 WHERE a > 3 LIMIT 5;
-- predicate: a > 3 ❌ (missing fetch=5)
```
## Root Cause
In `FilterExec::fmt_as`, the `TreeRender` branch only outputs the predicate:
```rust
DisplayFormatType::TreeRender => {
write!(f, "predicate={}", fmt_sql(self.predicate.as_ref()))
}
```
While `Default`/`Verbose` correctly includes fetch:
```rust
write!(f, "FilterExec: {}{}{}", self.predicate, display_projections, fetch)
```
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