Correct return type for initcap scalar function with utf8view (#13909) (#13934)

* Set utf8view as return type when input type is the same

* Verify that the returned type from call to scalar function matches the return type specified in the return_type function

* Match return type to utf8view

Co-authored-by: Tim Saucer <timsaucer@gmail.com>

Author: alamb

datafusion/functions/src/unicode/initcap.rs

@@ -63,7 +63,11 @@ impl ScalarUDFImpl for InitcapFunc {
     }
 
     fn return_type(&self, arg_types: &[DataType]) -> Result<DataType> {
-        utf8_to_str_type(&arg_types[0], "initcap")
+        if let DataType::Utf8View = arg_types[0] {
+            Ok(DataType::Utf8View)
+        } else {
+            utf8_to_str_type(&arg_types[0], "initcap")
+        }
     }
 
     fn invoke_batch(
@@ -188,7 +192,7 @@ mod tests {
     use crate::unicode::initcap::InitcapFunc;
     use crate::utils::test::test_function;
     use arrow::array::{Array, StringArray, StringViewArray};
-    use arrow::datatypes::DataType::Utf8;
+    use arrow::datatypes::DataType::{Utf8, Utf8View};
     use datafusion_common::{Result, ScalarValue};
     use datafusion_expr::{ColumnarValue, ScalarUDFImpl};
 
@@ -247,7 +251,7 @@ mod tests {
             )))],
             Ok(Some("Hi Thomas")),
             &str,
-            Utf8,
+            Utf8View,
             StringViewArray
         );
         test_function!(
@@ -257,7 +261,7 @@ mod tests {
             )))],
             Ok(Some("Hi Thomas With M0re Than 12 Chars")),
             &str,
-            Utf8,
+            Utf8View,
             StringViewArray
         );
         test_function!(
@@ -270,7 +274,7 @@ mod tests {
                 "Đẹp Đẽ Êm Ả Ñandú Árbol Олег Иванович Íslensku Þjóðarinnar Ελληνική"
             )),
             &str,
-            Utf8,
+            Utf8View,
             StringViewArray
         );
         test_function!(
@@ -280,15 +284,15 @@ mod tests {
             )))],
             Ok(Some("")),
             &str,
-            Utf8,
+            Utf8View,
             StringViewArray
         );
         test_function!(
             InitcapFunc::new(),
             vec![ColumnarValue::Scalar(ScalarValue::Utf8View(None))],
             Ok(None),
             &str,
-            Utf8,
+            Utf8View,
             StringViewArray
         );
 

datafusion/functions/src/utils.rs

@@ -154,6 +154,7 @@ pub mod test {
 
                     let result = result.unwrap().to_array(cardinality).expect("Failed to convert to array");
                     let result = result.as_any().downcast_ref::<$ARRAY_TYPE>().expect("Failed to convert to type");
+                    assert_eq!(result.data_type(), &$EXPECTED_DATA_TYPE);
 
                     // value is correct
                     match expected {