minor: Make FunctionRegistry udafs and udwfs methods mandatory (#17847)

* make FunctionRegistry `udaf` and `udwf` methods mandatory

* update upgrading guide

Author: milenkovicm

datafusion/core/tests/user_defined/user_defined_aggregates.rs

@@ -53,6 +53,7 @@ use datafusion::{
 };
 use datafusion_common::{assert_contains, exec_datafusion_err};
 use datafusion_common::{cast::as_primitive_array, exec_err};
+
 use datafusion_expr::expr::WindowFunction;
 use datafusion_expr::{
     col, create_udaf, function::AccumulatorArgs, AggregateUDFImpl, Expr,
@@ -297,10 +298,12 @@ async fn deregister_udaf() -> Result<()> {
     ctx.register_udaf(my_avg);
 
     assert!(ctx.state().aggregate_functions().contains_key("my_avg"));
+    assert!(datafusion_execution::FunctionRegistry::udafs(&ctx).contains("my_avg"));
 
     ctx.deregister_udaf("my_avg");
 
     assert!(!ctx.state().aggregate_functions().contains_key("my_avg"));
+    assert!(!datafusion_execution::FunctionRegistry::udafs(&ctx).contains("my_avg"));
 
     Ok(())
 }

datafusion/core/tests/user_defined/user_defined_scalar_functions.rs

@@ -775,10 +775,12 @@ async fn deregister_udf() -> Result<()> {
     ctx.register_udf(cast2i64);
 
     assert!(ctx.udfs().contains("cast_to_i64"));
+    assert!(FunctionRegistry::udfs(&ctx).contains("cast_to_i64"));
 
     ctx.deregister_udf("cast_to_i64");
 
     assert!(!ctx.udfs().contains("cast_to_i64"));
+    assert!(!FunctionRegistry::udfs(&ctx).contains("cast_to_i64"));
 
     Ok(())
 }

datafusion/core/tests/user_defined/user_defined_window_functions.rs

@@ -128,10 +128,12 @@ async fn test_deregister_udwf() -> Result<()> {
     OddCounter::register(&mut ctx, Arc::clone(&test_state));
 
     assert!(ctx.state().window_functions().contains_key("odd_counter"));
+    assert!(datafusion_execution::FunctionRegistry::udwfs(&ctx).contains("odd_counter"));
 
     ctx.deregister_udwf("odd_counter");
 
     assert!(!ctx.state().window_functions().contains_key("odd_counter"));
+    assert!(!datafusion_execution::FunctionRegistry::udwfs(&ctx).contains("odd_counter"));
 
     Ok(())
 }

datafusion/expr/src/registry.rs

@@ -31,20 +31,10 @@ pub trait FunctionRegistry {
     fn udfs(&self) -> HashSet<String>;
 
     /// Returns names of all available aggregate user defined functions.
-    fn udafs(&self) -> HashSet<String> {
-        // This default implementation is provided temporarily
-        // to maintain backward compatibility for the 50.1 release.
-        // It will be reverted to a required method in future versions.
-        HashSet::default()
-    }
+    fn udafs(&self) -> HashSet<String>;
 
     /// Returns names of all available window user defined functions.
-    fn udwfs(&self) -> HashSet<String> {
-        // This default implementation is provided temporarily
-        // to maintain backward compatibility for the 50.1 release.
-        // It will be reverted to a required method in future versions.
-        HashSet::default()
-    }
+    fn udwfs(&self) -> HashSet<String>;
 
     /// Returns a reference to the user defined scalar function (udf) named
     /// `name`.

docs/source/library-user-guide/upgrading.md

@@ -31,6 +31,25 @@ The Minimum Supported Rust Version (MSRV) has been updated to [`1.87.0`].
 
 [`1.87.0`]: https://releases.rs/docs/1.87.0/
 
+### `FunctionRegistry` exposes two additional methods
+
+`FunctionRegistry` exposes two additional methods `udafs` and `udwfs` which expose set of registered user defined aggregation and window function names. To upgrade implement methods returning set of registered function names:
+
+```diff
+impl FunctionRegistry for FunctionRegistryImpl {
+      fn udfs(&self) -> HashSet<String> {
+         self.scalar_functions.keys().cloned().collect()
+     }
++    fn udafs(&self) -> HashSet<String> {
++        self.aggregate_functions.keys().cloned().collect()
++    }
++
++    fn udwfs(&self) -> HashSet<String> {
++        self.window_functions.keys().cloned().collect()
++    }
+}
+```
+
 ### `datafusion-proto` use `TaskContext` rather than `SessionContext` in physical plan serde methods
 
 There have been changes in the public API methods of `datafusion-proto` which handle physical plan serde.