From 04673bbe160e8e52025d2ad022d4c344ec79122a Mon Sep 17 00:00:00 2001
From: Leonardo Scappatura <95079472+Leonard013@users.noreply.github.com>
Date: Sun, 12 Jul 2026 07:08:44 +0200
Subject: [PATCH] [FIX] Assign recalculated node state to backing field in
 _create_graph (#845)

`Workflow._create_graph` runs both over definition `Node`s (via `graph()`)
and over `NodeExecution` wrappers (via `execution_graph()`). Both expose
`state` as a read-only property, so recalculating a node's connection state
with `node.state = state.State(...)` raised

    AttributeError: property 'state' of 'NodeExecution' object has no setter

whenever a stateless node consumed the combined outputs of two upstream
split/combine nodes -- e.g. nested workflows using `.split(...).combine(...)`.

Assign to the `_state` backing field instead. For definition `Node`s this
sets the state exactly as before. For the transient `NodeExecution` wrapper
the write is inert, which is the correct behaviour: the underlying node's
state is already finalised during construction, and overwriting it in the
execution-graph pass mis-splits the node and produces empty results.

Adds a regression test that reproduces the reported nested split/combine
scenario (fails with AttributeError before, passes after).

Fixes #845

Co-authored-by: Claude <noreply@anthropic.com>
---
 pydra/compose/tests/test_workflow_run.py | 35 ++++++++++++++++++++++++
 pydra/engine/workflow.py                 |  2 +-
 2 files changed, 36 insertions(+), 1 deletion(-)

diff --git a/pydra/compose/tests/test_workflow_run.py b/pydra/compose/tests/test_workflow_run.py
index 7c34bdb4d..05609d819 100644
--- a/pydra/compose/tests/test_workflow_run.py
+++ b/pydra/compose/tests/test_workflow_run.py
@@ -867,6 +867,41 @@ def Worky(x, y):
     assert outputs.out == [11, 12, 22, 24, 33, 36]
 
 
+def test_wf_ndst_combine_two_upstreams(worker: str, tmp_path: Path):
+    """Regression test for GH#845.
+
+    A node with no splitter of its own that takes inputs from two separate
+    upstream nodes which have each been split and combined used to raise
+    ``AttributeError: property 'state' of 'NodeExecution' object has no setter``
+    while building the execution graph (``Workflow._create_graph``).
+    """
+
+    @python.define
+    def Step1(a: int) -> int:
+        return a
+
+    @python.define
+    def Step2(a: int, b: int) -> int:
+        return a + b
+
+    @python.define
+    def Step3(a: list, b: list) -> list:
+        return a
+
+    @workflow.define
+    def Worky(a: list):
+        step1 = workflow.add(Step1().split(a=a).combine("a"))
+        step2 = workflow.add(Step2().split(("a", "b"), a=a, b=step1.out).combine("a"))
+        step3 = workflow.add(Step3(a=step2.out, b=step1.out))
+        return step3.out
+
+    worky = Worky(a=[1, 2, 3])
+
+    outputs = worky(worker=worker, cache_root=tmp_path)
+
+    assert outputs.out == [2, 4, 6]
+
+
 # workflows with structures A ->  B -> C
 
 
diff --git a/pydra/engine/workflow.py b/pydra/engine/workflow.py
index c9e2d151f..8207c1782 100644
--- a/pydra/engine/workflow.py
+++ b/pydra/engine/workflow.py
@@ -388,7 +388,7 @@ def _create_graph(
                         new_other_states=other_states, new_combiner=combiner
                     )
                 else:
-                    node.state = state.State(
+                    node._state = state.State(
                         node.name,
                         splitter=None,
                         other_states=other_states,