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alamb pushed a commit to branch 59_maintenance
in repository https://gitbox.apache.org/repos/asf/arrow-rs.git


The following commit(s) were added to refs/heads/59_maintenance by this push:
     new c8a8df5e72 [59_maintenance] fix(arrow-array): preserve type params in 
`PrimitiveArray::into_builder` (#11448)
c8a8df5e72 is described below

commit c8a8df5e7236085753c7ed643900bdb0ec25e82f
Author: Jeffrey Vo <[email protected]>
AuthorDate: Fri Oct 9 03:26:13 2026 +0900

    [59_maintenance] fix(arrow-array): preserve type params in 
`PrimitiveArray::into_builder` (#11448)
    
    - Backport #11310 and #11321
    - For inclusion in https://github.com/apache/arrow-rs/issues/11352
    
    Cherry-pick of
    
https://github.com/apache/arrow-rs/commit/2f3cd82bea9f5baabdcc5b76efb4624620eeeb15
    and
    
https://github.com/apache/arrow-rs/commit/38054b7713eade3bd8092bbf0fc3eaad69d4ce65
    
    These are combined into a single PR since the fixes work on the same
    function
    
    ---------
    
    Co-authored-by: Neil Conway <[email protected]>
---
 arrow-array/src/array/dictionary_array.rs        | 22 +++++++++++++++++++++-
 arrow-array/src/array/primitive_array.rs         | 24 ++++++++++++++++++++++--
 arrow-array/src/builder/primitive_run_builder.rs | 11 +++++++++++
 3 files changed, 54 insertions(+), 3 deletions(-)

diff --git a/arrow-array/src/array/dictionary_array.rs 
b/arrow-array/src/array/dictionary_array.rs
index 0c465ec144..382af1a152 100644
--- a/arrow-array/src/array/dictionary_array.rs
+++ b/arrow-array/src/array/dictionary_array.rs
@@ -1061,7 +1061,7 @@ impl<K: ArrowDictionaryKeyType> AnyDictionaryArray for 
DictionaryArray<K> {
 mod tests {
     use super::*;
     use crate::cast::as_dictionary_array;
-    use crate::{Int8Array, Int16Array, Int32Array, RunArray, UInt8Array};
+    use crate::{Decimal128Array, Int8Array, Int16Array, Int32Array, RunArray, 
UInt8Array};
     use arrow_buffer::{Buffer, ToByteSlice};
 
     #[test]
@@ -1448,6 +1448,26 @@ mod tests {
         assert_eq!(expected, returned);
     }
 
+    #[test]
+    fn test_unary_mut_keeps_value_type() {
+        let values = || {
+            Decimal128Array::from(vec![123, 456])
+                .with_precision_and_scale(5, 2)
+                .unwrap()
+        };
+        let keys = Int8Array::from_iter_values([0, 1, 0]);
+        let dict = DictionaryArray::new(keys, Arc::new(values()));
+        let data_type = dict.data_type().clone();
+        let updated = dict.unary_mut::<_, Decimal128Type>(|x| x + 1).unwrap();
+        assert_eq!(updated.data_type(), &data_type);
+
+        // When the keys are shared, the original array is returned
+        let keys = Int8Array::from_iter_values([0, 1, 0]);
+        let dict = DictionaryArray::new(keys.clone(), Arc::new(values()));
+        let returned = dict.unary_mut::<_, Decimal128Type>(|x| x + 
1).unwrap_err();
+        assert_eq!(returned, DictionaryArray::new(keys, Arc::new(values())));
+    }
+
     #[test]
     fn test_occupancy() {
         let keys = Int32Array::new((100..200).collect(), None);
diff --git a/arrow-array/src/array/primitive_array.rs 
b/arrow-array/src/array/primitive_array.rs
index 8946af2b74..de20aaa271 100644
--- a/arrow-array/src/array/primitive_array.rs
+++ b/arrow-array/src/array/primitive_array.rs
@@ -1138,6 +1138,7 @@ impl<T: ArrowPrimitiveType> PrimitiveArray<T> {
     /// `Err(self)`
     pub fn into_builder(self) -> Result<PrimitiveBuilder<T>, Self> {
         let len = self.len();
+        let data_type = self.data_type.clone();
         let data = self.into_data();
         let null_bit_buffer = data.nulls().map(|b| b.inner().sliced());
 
@@ -1177,9 +1178,9 @@ impl<T: ArrowPrimitiveType> PrimitiveArray<T> {
         };
 
         match try_mutable_buffers {
-            Ok(builder) => Ok(builder),
+            Ok(builder) => Ok(builder.with_data_type(data_type)),
             Err((buffer, null_bit_buffer)) => {
-                let builder = ArrayData::builder(T::DATA_TYPE)
+                let builder = ArrayData::builder(data_type)
                     .len(len)
                     .add_buffer(buffer)
                     .null_bit_buffer(null_bit_buffer);
@@ -2869,6 +2870,25 @@ mod tests {
         }
     }
 
+    #[test]
+    fn test_into_builder_keeps_data_type() {
+        let array = Decimal128Array::from(vec![1, 2])
+            .with_precision_and_scale(10, 2)
+            .unwrap();
+        let data_type = array.data_type().clone();
+
+        // Shared buffers: the array is returned
+        let shared = array.clone();
+        let array = array.into_builder().unwrap_err();
+        assert_eq!(array.data_type(), &data_type);
+        drop(shared);
+
+        // Unshared buffers: the buffers are reused by the builder
+        let mut builder = array.into_builder().unwrap();
+        builder.append_value(3);
+        assert_eq!(builder.finish().data_type(), &data_type);
+    }
+
     #[test]
     fn test_into_builder_on_sliced_array() {
         let array: Int32Array = vec![1, 2, 3].into_iter().map(Some).collect();
diff --git a/arrow-array/src/builder/primitive_run_builder.rs 
b/arrow-array/src/builder/primitive_run_builder.rs
index 17beffdffa..832c40bb9b 100644
--- a/arrow-array/src/builder/primitive_run_builder.rs
+++ b/arrow-array/src/builder/primitive_run_builder.rs
@@ -378,4 +378,15 @@ mod tests {
         let values = array.values();
         assert_eq!(values.timezone(), Some("Europe/Paris"));
     }
+
+    #[test]
+    fn test_finish_cloned_keeps_data_type() {
+        let data_type = DataType::Decimal128(5, 2);
+        let mut builder = PrimitiveRunBuilder::<Int16Type, 
Decimal128Type>::new()
+            .with_data_type(data_type.clone());
+        // Leave the run open, so `finish_cloned` has to add it to a copy of 
the values
+        builder.append_value(123);
+        let array = builder.finish_cloned();
+        assert_eq!(array.values().data_type(), &data_type);
+    }
 }

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