fix: serialize user-defined window functions to proto

datafusion/physical-plan/src/windows/mod.rs

@@ -198,7 +198,7 @@ pub fn create_udwf_window_expr(
 
 /// Implements [`BuiltInWindowFunctionExpr`] for [`WindowUDF`]
 #[derive(Clone, Debug)]
-struct WindowUDFExpr {
+pub struct WindowUDFExpr {
     fun: Arc<WindowUDF>,
     args: Vec<Arc<dyn PhysicalExpr>>,
     /// Display name
@@ -213,6 +213,12 @@ struct WindowUDFExpr {
     ignore_nulls: bool,
 }
 
+impl WindowUDFExpr {
+    pub fn fun(&self) -> &Arc<WindowUDF> {
+        &self.fun
+    }
+}
+
 impl BuiltInWindowFunctionExpr for WindowUDFExpr {
     fn as_any(&self) -> &dyn std::any::Any {
         self

datafusion/proto/proto/datafusion.proto

@@ -868,6 +868,7 @@ message PhysicalWindowExprNode {
   oneof window_function {
     BuiltInWindowFunction built_in_function = 2;
     string user_defined_aggr_function = 3;
+    string user_defined_window_function = 10;
   }
   repeated PhysicalExprNode args = 4;
   repeated PhysicalExprNode partition_by = 5;

datafusion/proto/src/physical_plan/from_proto.rs

@@ -161,6 +161,12 @@ pub fn parse_physical_window_expr(
                     None => registry.udaf(udaf_name)?
                 })
             }
+            protobuf::physical_window_expr_node::WindowFunction::UserDefinedWindowFunction(udwf_name) => {
+                WindowFunctionDefinition::WindowUDF(match &proto.fun_definition {
+                    Some(buf) => codec.try_decode_udwf(udwf_name, buf)?,
+                    None => registry.udwf(udwf_name)?
+                })
+            }
         }
     } else {
         return Err(proto_error("Missing required field in protobuf"));

datafusion/proto/src/physical_plan/mod.rs

@@ -64,7 +64,7 @@ use datafusion::physical_plan::{
     ExecutionPlan, InputOrderMode, PhysicalExpr, WindowExpr,
 };
 use datafusion_common::{internal_err, not_impl_err, DataFusionError, Result};
-use datafusion_expr::{AggregateUDF, ScalarUDF};
+use datafusion_expr::{AggregateUDF, ScalarUDF, WindowUDF};
 
 use crate::common::{byte_to_string, str_to_byte};
 use crate::physical_plan::from_proto::{
@@ -2119,6 +2119,14 @@ pub trait PhysicalExtensionCodec: Debug + Send + Sync {
     fn try_encode_udaf(&self, _node: &AggregateUDF, _buf: &mut Vec<u8>) -> Result<()> {
         Ok(())
     }
+
+    fn try_decode_udwf(&self, name: &str, _buf: &[u8]) -> Result<Arc<WindowUDF>> {
+        not_impl_err!("PhysicalExtensionCodec is not provided for window function {name}")
+    }
+
+    fn try_encode_udwf(&self, _node: &WindowUDF, _buf: &mut Vec<u8>) -> Result<()> {
+        Ok(())
+    }
 }
 
 #[derive(Debug)]

datafusion/proto/src/physical_plan/to_proto.rs

@@ -19,14 +19,14 @@ use std::sync::Arc;
 
 #[cfg(feature = "parquet")]
 use datafusion::datasource::file_format::parquet::ParquetSink;
-use datafusion::physical_expr::window::SlidingAggregateWindowExpr;
+use datafusion::physical_expr::window::{BuiltInWindowExpr, SlidingAggregateWindowExpr};
 use datafusion::physical_expr::{LexOrdering, PhysicalSortExpr, ScalarFunctionExpr};
 use datafusion::physical_plan::expressions::{
     BinaryExpr, CaseExpr, CastExpr, Column, InListExpr, IsNotNullExpr, IsNullExpr,
     Literal, NegativeExpr, NotExpr, TryCastExpr,
 };
 use datafusion::physical_plan::udaf::AggregateFunctionExpr;
-use datafusion::physical_plan::windows::PlainAggregateWindowExpr;
+use datafusion::physical_plan::windows::{PlainAggregateWindowExpr, WindowUDFExpr};
 use datafusion::physical_plan::{Partitioning, PhysicalExpr, WindowExpr};
 use datafusion::{
     datasource::{
@@ -68,7 +68,7 @@ pub fn serialize_physical_aggr_expr(
                 ordering_req,
                 distinct: aggr_expr.is_distinct(),
                 ignore_nulls: aggr_expr.ignore_nulls(),
-                fun_definition: (!buf.is_empty()).then_some(buf)
+                fun_definition: (!buf.is_empty()).then_some(buf),
             },
         )),
     })
@@ -120,6 +120,25 @@ pub fn serialize_physical_window_expr(
             window_frame,
             codec,
         )?
+    } else if let Some(built_in_window_expr) = expr.downcast_ref::<BuiltInWindowExpr>() {
+        if let Some(expr) = built_in_window_expr
+            .get_built_in_func_expr()
+            .as_any()
+            .downcast_ref::<WindowUDFExpr>()
+        {
+            let mut buf = Vec::new();
+            codec.try_encode_udwf(expr.fun(), &mut buf)?;
+            (
+                physical_window_expr_node::WindowFunction::UserDefinedWindowFunction(
+                    expr.fun().name().to_string(),
+                ),
+                (!buf.is_empty()).then_some(buf),
+            )
+        } else {
+            return not_impl_err!(
+                "User-defined window function not supported: {window_expr:?}"
+            );
+        }
     } else {
         return not_impl_err!("WindowExpr not supported: {window_expr:?}");
     };

datafusion/proto/tests/cases/mod.rs

@@ -15,15 +15,18 @@
 // specific language governing permissions and limitations
 // under the License.
 
+use arrow::datatypes::{DataType, Field};
 use std::any::Any;
-
-use arrow::datatypes::DataType;
+use std::fmt::Debug;
 
 use datafusion_common::plan_err;
 use datafusion_expr::function::AccumulatorArgs;
 use datafusion_expr::{
-    Accumulator, AggregateUDFImpl, ColumnarValue, ScalarUDFImpl, Signature, Volatility,
+    Accumulator, AggregateUDFImpl, ColumnarValue, PartitionEvaluator, ScalarUDFImpl,
+    Signature, Volatility, WindowUDFImpl,
 };
+use datafusion_functions_window_common::field::WindowUDFFieldArgs;
+use datafusion_functions_window_common::partition::PartitionEvaluatorArgs;
 
 mod roundtrip_logical_plan;
 mod roundtrip_physical_plan;
@@ -125,3 +128,54 @@ pub struct MyAggregateUdfNode {
     #[prost(string, tag = "1")]
     pub result: String,
 }
+
+#[derive(Debug)]
+pub(in crate::cases) struct CustomUDWF {
+    signature: Signature,
+    payload: String,
+}
+
+impl CustomUDWF {
+    pub fn new(payload: String) -> Self {
+        Self {
+            signature: Signature::exact(vec![DataType::Int64], Volatility::Immutable),
+            payload,
+        }
+    }
+}
+
+impl WindowUDFImpl for CustomUDWF {
+    fn as_any(&self) -> &dyn Any {
+        self
+    }
+
+    fn name(&self) -> &str {
+        "custom_udwf"
+    }
+
+    fn signature(&self) -> &Signature {
+        &self.signature
+    }
+
+    fn partition_evaluator(
+        &self,
+        _partition_evaluator_args: PartitionEvaluatorArgs,
+    ) -> datafusion_common::Result<Box<dyn PartitionEvaluator>> {
+        Ok(Box::new(CustomUDWFEvaluator {}))
+    }
+
+    fn field(&self, field_args: WindowUDFFieldArgs) -> datafusion_common::Result<Field> {
+        Ok(Field::new(field_args.name(), DataType::UInt64, false))
+    }
+}
+
+#[derive(Debug)]
+struct CustomUDWFEvaluator;
+
+impl PartitionEvaluator for CustomUDWFEvaluator {}
+
+#[derive(Clone, PartialEq, ::prost::Message)]
+pub(in crate::cases) struct CustomUDWFNode {
+    #[prost(string, tag = "1")]
+    pub payload: String,
+}