Fix ScalarStructBuilder::build() for an empty struct (#16205)

* Fix ScalarStructBuilder::build() when the struct is empty

This had been broken by apache/arrow-rs#7247 in Arrow 55.1.0

* fix test for error

Author: Blizzara

datafusion/common/src/scalar/mod.rs

@@ -4179,7 +4179,7 @@ mod tests {
 
     #[test]
     #[should_panic(
-        expected = "Error building ScalarValue::Struct. Expected array with exactly one element, found array with 4 elements"
+        expected = "InvalidArgumentError(\"Incorrect array length for StructArray field \\\"bool\\\", expected 1 got 4\")"
     )]
     fn test_scalar_value_from_for_struct_should_panic() {
         let _ = ScalarStructBuilder::new()

datafusion/common/src/scalar/struct_builder.rs

@@ -17,7 +17,6 @@
 
 //! [`ScalarStructBuilder`] for building [`ScalarValue::Struct`]
 
-use crate::error::_internal_err;
 use crate::{Result, ScalarValue};
 use arrow::array::{ArrayRef, StructArray};
 use arrow::datatypes::{DataType, Field, FieldRef, Fields};
@@ -109,17 +108,8 @@ impl ScalarStructBuilder {
     pub fn build(self) -> Result<ScalarValue> {
         let Self { fields, arrays } = self;
 
-        for array in &arrays {
-            if array.len() != 1 {
-                return _internal_err!(
-                    "Error building ScalarValue::Struct. \
-                Expected array with exactly one element, found array with {} elements",
-                    array.len()
-                );
-            }
-        }
-
-        let struct_array = StructArray::try_new(Fields::from(fields), arrays, None)?;
+        let struct_array =
+            StructArray::try_new_with_length(Fields::from(fields), arrays, None, 1)?;
         Ok(ScalarValue::Struct(Arc::new(struct_array)))
     }
 }
@@ -181,3 +171,15 @@ impl IntoFields for Vec<Field> {
         Fields::from(self)
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    // Other cases are tested by doc tests
+    #[test]
+    fn test_empty_struct() {
+        let sv = ScalarStructBuilder::new().build().unwrap();
+        assert_eq!(format!("{sv}"), "{}");
+    }
+}