ModelGraph only stops ancestry check at model defined named_vars

pymc/model_graph.py

@@ -62,8 +62,11 @@ def _filter_non_parameter_inputs(var):
                 # Otherwise return all inputs
                 return node.inputs
 
+        blockers = set(self.model.named_vars)
+
         def _expand(x):
-            if x.name:
+            nonlocal blockers
+            if x.name in blockers:
                 return [x]
             if isinstance(x.owner, Apply):
                 return reversed(_filter_non_parameter_inputs(x))

pymc/tests/test_model_graph.py

@@ -407,3 +407,18 @@ def test_subgraph(self, var_names, vars_to_plot, compute_graph):
 
 class TestModelNonRandomVariableRVs(BaseModelGraphTest):
     model_func = model_non_random_variable_rvs
+
+
+def test_model_graph_with_intermediate_named_variables():
+    # Issue 6421
+    with pm.Model() as m1:
+        a = pm.Normal("a", 0, 1, shape=3)
+        pm.Normal("b", a.mean(axis=-1), 1)
+    assert dict(ModelGraph(m1).make_compute_graph()) == {"a": set(), "b": {"a"}}
+
+    with pm.Model() as m2:
+        a = pm.Normal("a", 0, 1)
+        b = a + 1
+        b.name = "b"
+        pm.Normal("c", b, 1)
+    assert dict(ModelGraph(m2).make_compute_graph()) == {"a": set(), "c": {"a"}}