From e17342cc6801f341eba8ee8262785c21dd0a9c2a Mon Sep 17 00:00:00 2001
From: Andy Grove <agrove@apache.org>
Date: Tue, 10 Dec 2024 08:55:26 -0700
Subject: [PATCH] Deprecate ScalarUDFImpl::return_type and revert a breaking
 API change

---
 datafusion/expr/src/udf.rs                     | 4 ++++
 datafusion/functions/src/datetime/date_part.rs | 4 +++-
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/datafusion/expr/src/udf.rs b/datafusion/expr/src/udf.rs
index 809c78f30eff..238bc3bcbeca 100644
--- a/datafusion/expr/src/udf.rs
+++ b/datafusion/expr/src/udf.rs
@@ -174,6 +174,7 @@ impl ScalarUDF {
     ///
     /// See [`ScalarUDFImpl::return_type`] for more details.
     pub fn return_type(&self, arg_types: &[DataType]) -> Result<DataType> {
+        #[allow(deprecated)]
         self.inner.return_type(arg_types)
     }
 
@@ -450,6 +451,7 @@ pub trait ScalarUDFImpl: Debug + Send + Sync {
     /// is recommended to return [`DataFusionError::Internal`].
     ///
     /// [`DataFusionError::Internal`]: datafusion_common::DataFusionError::Internal
+    #[deprecated(since = "44.0.0", note = "Use `return_type_from_exprs` instead")]
     fn return_type(&self, arg_types: &[DataType]) -> Result<DataType>;
 
     /// What [`DataType`] will be returned by this function, given the
@@ -483,6 +485,7 @@ pub trait ScalarUDFImpl: Debug + Send + Sync {
         _schema: &dyn ExprSchema,
         arg_types: &[DataType],
     ) -> Result<DataType> {
+        #[allow(deprecated)]
         self.return_type(arg_types)
     }
 
@@ -756,6 +759,7 @@ impl ScalarUDFImpl for AliasedScalarUDFImpl {
     }
 
     fn return_type(&self, arg_types: &[DataType]) -> Result<DataType> {
+        #[allow(deprecated)]
         self.inner.return_type(arg_types)
     }
 
diff --git a/datafusion/functions/src/datetime/date_part.rs b/datafusion/functions/src/datetime/date_part.rs
index b8c58a11d999..03387d58b44d 100644
--- a/datafusion/functions/src/datetime/date_part.rs
+++ b/datafusion/functions/src/datetime/date_part.rs
@@ -148,7 +148,9 @@ impl ScalarUDFImpl for DatePartFunc {
     }
 
     fn return_type(&self, _arg_types: &[DataType]) -> Result<DataType> {
-        internal_err!("return_type_from_exprs shoud be called instead")
+        // return type could be Float32 or Int32 depending on the input arguments
+        // return_type_from_exprs should be called instead
+        Ok(DataType::Float64)
     }
 
     fn return_type_from_exprs(