Make lower and upper emit Utf8View for Utf8View input (#20616)

## Which issue does this PR close?

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- Part of #20585

## Rationale for this change

String UDFs should preserve string representation where feasible. lower
and upper previously accepted Utf8View input but emitted Utf8, causing
an unnecessary type downgrade. This aligns both with the expected
behavior of returning the same string type as its primary input.

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in the issue then this section is not needed.
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your changes and offer better suggestions for fixes.
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## What changes are included in this PR?

- Updated lower and upper return type inference to emit Utf8View when
input is Utf8View


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## Are these changes tested?

Yes
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Author: kumarUjjawal

datafusion/functions/src/string/common.rs

@@ -22,7 +22,7 @@ use std::sync::Arc;
 use crate::strings::make_and_append_view;
 use arrow::array::{
     Array, ArrayRef, GenericStringArray, GenericStringBuilder, NullBufferBuilder,
-    OffsetSizeTrait, StringBuilder, StringViewArray, new_null_array,
+    OffsetSizeTrait, StringViewArray, StringViewBuilder, new_null_array,
 };
 use arrow::buffer::{Buffer, ScalarBuffer};
 use arrow::datatypes::DataType;
@@ -358,10 +358,8 @@ where
             >(array, op)?)),
             DataType::Utf8View => {
                 let string_array = as_string_view_array(array)?;
-                let mut string_builder = StringBuilder::with_capacity(
-                    string_array.len(),
-                    string_array.get_array_memory_size(),
-                );
+                let mut string_builder =
+                    StringViewBuilder::with_capacity(string_array.len());
 
                 for str in string_array.iter() {
                     if let Some(str) = str {
@@ -386,7 +384,7 @@ where
             }
             ScalarValue::Utf8View(a) => {
                 let result = a.as_ref().map(|x| op(x));
-                Ok(ColumnarValue::Scalar(ScalarValue::Utf8(result)))
+                Ok(ColumnarValue::Scalar(ScalarValue::Utf8View(result)))
             }
             other => exec_err!("Unsupported data type {other:?} for function {name}"),
         },

datafusion/functions/src/string/lower.rs

@@ -19,7 +19,6 @@ use arrow::datatypes::DataType;
 use std::any::Any;
 
 use crate::string::common::to_lower;
-use crate::utils::utf8_to_str_type;
 use datafusion_common::Result;
 use datafusion_common::types::logical_string;
 use datafusion_expr::{
@@ -82,7 +81,7 @@ impl ScalarUDFImpl for LowerFunc {
     }
 
     fn return_type(&self, arg_types: &[DataType]) -> Result<DataType> {
-        utf8_to_str_type(&arg_types[0], "lower")
+        Ok(arg_types[0].clone())
     }
 
     fn invoke_with_args(&self, args: ScalarFunctionArgs) -> Result<ColumnarValue> {
@@ -97,8 +96,7 @@ impl ScalarUDFImpl for LowerFunc {
 #[cfg(test)]
 mod tests {
     use super::*;
-    use arrow::array::{Array, ArrayRef, StringArray};
-    use arrow::datatypes::DataType::Utf8;
+    use arrow::array::{Array, ArrayRef, StringArray, StringViewArray};
     use arrow::datatypes::Field;
     use datafusion_common::config::ConfigOptions;
     use std::sync::Arc;
@@ -111,7 +109,7 @@ mod tests {
             number_rows: input.len(),
             args: vec![ColumnarValue::Array(input)],
             arg_fields,
-            return_field: Field::new("f", Utf8, true).into(),
+            return_field: Field::new("f", expected.data_type().clone(), true).into(),
             config_options: Arc::new(ConfigOptions::default()),
         };
 
@@ -197,4 +195,21 @@ mod tests {
 
         to_lower(input, expected)
     }
+
+    #[test]
+    fn lower_utf8view() -> Result<()> {
+        let input = Arc::new(StringViewArray::from(vec![
+            Some("ARROW"),
+            None,
+            Some("TSCHÜSS"),
+        ])) as ArrayRef;
+
+        let expected = Arc::new(StringViewArray::from(vec![
+            Some("arrow"),
+            None,
+            Some("tschüss"),
+        ])) as ArrayRef;
+
+        to_lower(input, expected)
+    }
 }

datafusion/functions/src/string/upper.rs

@@ -16,7 +16,6 @@
 // under the License.
 
 use crate::string::common::to_upper;
-use crate::utils::utf8_to_str_type;
 use arrow::datatypes::DataType;
 use datafusion_common::Result;
 use datafusion_common::types::logical_string;
@@ -81,7 +80,7 @@ impl ScalarUDFImpl for UpperFunc {
     }
 
     fn return_type(&self, arg_types: &[DataType]) -> Result<DataType> {
-        utf8_to_str_type(&arg_types[0], "upper")
+        Ok(arg_types[0].clone())
     }
 
     fn invoke_with_args(&self, args: ScalarFunctionArgs) -> Result<ColumnarValue> {
@@ -96,8 +95,7 @@ impl ScalarUDFImpl for UpperFunc {
 #[cfg(test)]
 mod tests {
     use super::*;
-    use arrow::array::{Array, ArrayRef, StringArray};
-    use arrow::datatypes::DataType::Utf8;
+    use arrow::array::{Array, ArrayRef, StringArray, StringViewArray};
     use arrow::datatypes::Field;
     use datafusion_common::config::ConfigOptions;
     use std::sync::Arc;
@@ -110,7 +108,7 @@ mod tests {
             number_rows: input.len(),
             args: vec![ColumnarValue::Array(input)],
             arg_fields: vec![arg_field],
-            return_field: Field::new("f", Utf8, true).into(),
+            return_field: Field::new("f", expected.data_type().clone(), true).into(),
             config_options: Arc::new(ConfigOptions::default()),
         };
 
@@ -196,4 +194,21 @@ mod tests {
 
         to_upper(input, expected)
     }
+
+    #[test]
+    fn upper_utf8view() -> Result<()> {
+        let input = Arc::new(StringViewArray::from(vec![
+            Some("arrow"),
+            None,
+            Some("tschüß"),
+        ])) as ArrayRef;
+
+        let expected = Arc::new(StringViewArray::from(vec![
+            Some("ARROW"),
+            None,
+            Some("TSCHÜSS"),
+        ])) as ArrayRef;
+
+        to_upper(input, expected)
+    }
 }

datafusion/sqllogictest/test_files/functions.slt

@@ -435,6 +435,11 @@ SELECT upper(arrow_cast('foo', 'Dictionary(Int32, Utf8)'))
 ----
 FOO
 
+query T
+SELECT upper(arrow_cast(arrow_cast('foo', 'Dictionary(Int32, Utf8)'), 'Dictionary(Int32, Utf8View)'))
+----
+FOO
+
 query T
 SELECT upper('árvore ação αβγ')
 ----
@@ -445,6 +450,26 @@ SELECT upper(arrow_cast('árvore ação αβγ', 'Dictionary(Int32, Utf8)'))
 ----
 ÁRVORE AÇÃO ΑΒΓ
 
+query T
+SELECT arrow_typeof(upper('foo'))
+----
+Utf8
+
+query T
+SELECT arrow_typeof(upper(arrow_cast('foo', 'LargeUtf8')))
+----
+LargeUtf8
+
+query T
+SELECT arrow_typeof(upper(arrow_cast('foo', 'Utf8View')))
+----
+Utf8View
+
+query T
+SELECT arrow_typeof(upper(arrow_cast(arrow_cast('foo', 'Dictionary(Int32, Utf8)'), 'Dictionary(Int32, Utf8View)')))
+----
+Utf8View
+
 query T
 SELECT btrim('   foo  ')
 ----
@@ -490,6 +515,11 @@ SELECT lower(arrow_cast('FOObar', 'Dictionary(Int32, Utf8)'))
 ----
 foobar
 
+query T
+SELECT lower(arrow_cast(arrow_cast('FOObar', 'Dictionary(Int32, Utf8)'), 'Dictionary(Int32, Utf8View)'))
+----
+foobar
+
 query T
 SELECT lower('ÁRVORE AÇÃO ΑΒΓ')
 ----
@@ -500,6 +530,26 @@ SELECT lower(arrow_cast('ÁRVORE AÇÃO ΑΒΓ', 'Dictionary(Int32, Utf8)'))
 ----
 árvore ação αβγ
 
+query T
+SELECT arrow_typeof(lower('FOObar'))
+----
+Utf8
+
+query T
+SELECT arrow_typeof(lower(arrow_cast('FOObar', 'LargeUtf8')))
+----
+LargeUtf8
+
+query T
+SELECT arrow_typeof(lower(arrow_cast('FOObar', 'Utf8View')))
+----
+Utf8View
+
+query T
+SELECT arrow_typeof(lower(arrow_cast(arrow_cast('FOObar', 'Dictionary(Int32, Utf8)'), 'Dictionary(Int32, Utf8View)')))
+----
+Utf8View
+
 query T
 SELECT ltrim('   foo')
 ----