Only add dim_length shared variable when adding a new coordinate

pymc/model/core.py

@@ -964,6 +964,7 @@ def add_coord(
         if name in self.coords:
             if not np.array_equal(values, self.coords[name]):
                 raise ValueError(f"Duplicate and incompatible coordinate: {name}.")
+            return
         if length is not None and not isinstance(length, int | Variable):
             raise ValueError(
                 f"The `length` passed for the '{name}' coord must be an int, PyTensor Variable or None."

tests/model/test_core.py

@@ -33,6 +33,7 @@
 import scipy.stats as st
 
 from pytensor.graph import graph_inputs
+from pytensor.graph.basic import get_var_by_name
 from pytensor.raise_op import Assert
 from pytensor.tensor.random.op import RandomVariable
 from pytensor.tensor.variable import TensorConstant
@@ -858,6 +859,19 @@ def test_nested_model_coords():
     assert set(m2.named_vars_to_dims) < set(m1.named_vars_to_dims)
 
 
+def test_multiple_add_coords_with_same_name():
+    coord = {"dim1": ["a", "b", "c"]}
+    with pm.Model(coords=coord) as m:
+        a = pm.Normal("a", dims="dim1")
+        with pm.Model(coords=coord) as nested_m:
+            b = pm.Normal("b", dims="dim1")
+        m.add_coords(coord)
+        c = pm.Normal("c", dims="dim1")
+        d = pm.Deterministic("d", a + b + c)
+    variables = get_var_by_name([d], "dim1")
+    assert len(variables) == 1 and variables[0] is m.dim_lengths["dim1"]
+
+
 class TestSetUpdateCoords:
     def test_shapeerror_from_set_data_dimensionality(self):
         with pm.Model() as pmodel: