Add FutureWarning to SumTo1 transform deprecation

pymc/distributions/transforms.py

@@ -12,6 +12,8 @@
 #   See the License for the specific language governing permissions and
 #   limitations under the License.
 
+import warnings
+
 from functools import singledispatch
 
 import numpy as np
@@ -123,6 +125,14 @@ class SumTo1(Transform):
 
     name = "sumto1"
 
+    def __init__(self):
+        warnings.warn(
+            "SumTo1 is deprecated and will be removed in a future version. "
+            "Use the Simplex transform instead.",
+            FutureWarning,
+            stacklevel=2,
+        )
+
     def backward(self, value, *inputs):
         remaining = 1 - pt.sum(value[..., :], axis=-1, keepdims=True)
         return pt.concatenate([value[..., :], remaining], axis=-1)

tests/distributions/test_transform.py

@@ -160,6 +160,11 @@ def test_sum_to_1():
     )
 
 
+def test_sum_to_1_deprecation_warning():
+    with pytest.warns(FutureWarning, match="SumTo1 is deprecated"):
+        tr.SumTo1()
+
+
 def test_log():
     check_transform(tr.log, Rplusbig)