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new e6fb133e50 fix(arrow-array): reset NullBuilder length in finish
(#11110)
e6fb133e50 is described below
commit e6fb133e506012e683f6f4207bfcf039a7221194
Author: ranflarion <[email protected]>
AuthorDate: Wed Sep 16 20:00:06 2026 -0400
fix(arrow-array): reset NullBuilder length in finish (#11110)
# Which issue does this PR close?
- Closes #11109.
# Rationale for this change
`NullBuilder::finish` is documented to reset the builder but its body is
the same as `finish_cloned`, so a builder reused across `finish` calls
emits cumulative lengths. Every other builder resets on `finish`.
# What changes are included in this PR?
`finish` takes the length with `std::mem::take`, leaving the builder
empty. `finish_cloned` is unchanged.
# Are these changes tested?
Yes. `test_null_array_builder_finish_resets` finishes twice and checks
the builder is empty in between; it fails on `main` (`left: 0, right:
10`) and passes with the change. `cargo test -p arrow-array`, `-p
arrow-csv` and `-p parquet-variant-compute` pass; the two other in-tree
callers of `NullBuilder::finish` each finish a fresh builder once, so
their output does not change.
# Are there any user-facing changes?
`NullBuilder::finish` now resets the builder as documented. Code that
relied on the previous non-resetting behavior would see shorter arrays
from subsequent `finish` calls; that behavior contradicted the doc
comment and every other builder. No API changes.
---
arrow-array/src/builder/null_builder.rs | 18 +++++++++++++++++-
1 file changed, 17 insertions(+), 1 deletion(-)
diff --git a/arrow-array/src/builder/null_builder.rs
b/arrow-array/src/builder/null_builder.rs
index 9dab231b40..0f52be9ae9 100644
--- a/arrow-array/src/builder/null_builder.rs
+++ b/arrow-array/src/builder/null_builder.rs
@@ -85,7 +85,7 @@ impl NullBuilder {
/// Builds the [NullArray] and reset this builder.
pub fn finish(&mut self) -> NullArray {
- let len = self.len();
+ let len = std::mem::take(&mut self.len);
let builder = ArrayData::new_null(&DataType::Null, len).into_builder();
// SAFETY: ArrayData::new_null produces valid null array data, so all
builder invariants hold
@@ -169,4 +169,20 @@ mod tests {
array = builder.finish();
assert_eq!(10, array.len());
}
+
+ #[test]
+ fn test_null_array_builder_finish_resets() {
+ let mut builder = NullBuilder::new();
+ builder.append_nulls(10);
+
+ let array = builder.finish();
+ assert_eq!(10, array.len());
+ assert_eq!(0, builder.len());
+ assert!(builder.is_empty());
+
+ builder.append_nulls(3);
+ let array = builder.finish();
+ assert_eq!(3, array.len());
+ assert_eq!(0, builder.len());
+ }
}
