fix(udf): name property reports FFI capsule name, not the ignored ctor arg

Previously `ScalarUDF.name`, `AggregateUDF.name`, and `WindowUDF.name`
cached the `name` argument passed to `__init__`. The FFI-capsule branch
discards that argument and constructs from the capsule directly, so the
cached value was wrong — e.g. `udf(IsNullUDF()).name` returned
`"<class 'datafusion_ffi_example.IsNullUDF'>"` (the factory-synthesized
string from `from_pycapsule`) rather than the capsule's own
`my_custom_is_null`.

Expose a `name` getter on `PyScalarUDF`, `PyAggregateUDF`, `PyWindowUDF`
that forwards to the underlying `UDF::name()`, and have each Python
property delegate to it. Same path for Python-defined and
FFI-imported UDFs, no stale cache.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: timsaucer

crates/core/src/udaf.rs

@@ -368,4 +368,9 @@ impl PyAggregateUDF {
     fn __repr__(&self) -> PyResult<String> {
         Ok(format!("AggregateUDF({})", self.function.name()))
     }
+
+    #[getter]
+    fn name(&self) -> &str {
+        self.function.name()
+    }
 }

crates/core/src/udf.rs

@@ -261,4 +261,9 @@ impl PyScalarUDF {
     fn __repr__(&self) -> PyResult<String> {
         Ok(format!("ScalarUDF({})", self.function.name()))
     }
+
+    #[getter]
+    fn name(&self) -> &str {
+        self.function.name()
+    }
 }

crates/core/src/udwf.rs

@@ -273,6 +273,11 @@ impl PyWindowUDF {
     fn __repr__(&self) -> PyResult<String> {
         Ok(format!("WindowUDF({})", self.function.name()))
     }
+
+    #[getter]
+    fn name(&self) -> &str {
+        self.function.name()
+    }
 }
 
 #[derive(Debug)]

python/datafusion/user_defined.py

@@ -132,7 +132,6 @@ def __init__(
 
         See helper method :py:func:`udf` for argument details.
         """
-        self._name = name
         if hasattr(func, "__datafusion_scalar_udf__"):
             self._udf = df_internal.ScalarUDF.from_pycapsule(func)
             return
@@ -144,8 +143,13 @@ def __init__(
 
     @property
     def name(self) -> str:
-        """Return the registered name of this UDF."""
-        return self._name
+        """Return the registered name of this UDF.
+
+        For UDFs imported via the FFI capsule protocol, this is the
+        name the capsule itself reports — not the ``name`` argument
+        passed to the constructor (which is ignored on the FFI path).
+        """
+        return self._udf.name
 
     def __repr__(self) -> str:
         """Print a string representation of the Scalar UDF."""
@@ -400,7 +404,6 @@ def __init__(
         See :py:func:`udaf` for a convenience function and argument
         descriptions.
         """
-        self._name = name
         if hasattr(accumulator, "__datafusion_aggregate_udf__"):
             self._udaf = df_internal.AggregateUDF.from_pycapsule(accumulator)
             return
@@ -427,8 +430,13 @@ def __init__(
 
     @property
     def name(self) -> str:
-        """Return the registered name of this UDAF."""
-        return self._name
+        """Return the registered name of this UDAF.
+
+        For UDAFs imported via the FFI capsule protocol, this is the
+        name the capsule itself reports — not the ``name`` argument
+        passed to the constructor (which is ignored on the FFI path).
+        """
+        return self._udaf.name
 
     def __repr__(self) -> str:
         """Print a string representation of the Aggregate UDF."""
@@ -833,7 +841,6 @@ def __init__(
         See :py:func:`udwf` for a convenience function and argument
         descriptions.
         """
-        self._name = name
         if hasattr(func, "__datafusion_window_udf__"):
             self._udwf = df_internal.WindowUDF.from_pycapsule(func)
             return
@@ -843,8 +850,13 @@ def __init__(
 
     @property
     def name(self) -> str:
-        """Return the registered name of this UDWF."""
-        return self._name
+        """Return the registered name of this UDWF.
+
+        For UDWFs imported via the FFI capsule protocol, this is the
+        name the capsule itself reports — not the ``name`` argument
+        passed to the constructor (which is ignored on the FFI path).
+        """
+        return self._udwf.name
 
     def __repr__(self) -> str:
         """Print a string representation of the Window UDF."""