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CFnV2: GetAtt function searches first into resource results #13280

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Merged
merged 2 commits into from
Oct 23, 2025
Merged

CFnV2: GetAtt function searches first into resource results #13280

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CFnV2: GetAtt looks first into resource results
pinzon Oct 17, 2025
6620515
nit improvment
pinzon Oct 22, 2025
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29 changes: 16 additions & 13 deletions localstack-core/localstack/services/cloudformation/engine/v2/change_set_model_preproc.py
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Original file line number Diff line number Diff line change
Expand Up @@ -597,26 +597,29 @@ def _resolve_attribute(self, arguments: str | list[str], select_before: bool) ->
f"Template format error: Unresolved resource dependencies [{logical_name_of_resource}] in the Resources block of the template"
)

# Custom Resources can mutate their definition
# So the preproc should search first in the resource values and then check the template
if select_before:
value = self._before_deployed_property_value_of(
resource_logical_id=logical_name_of_resource,
property_name=attribute_name,
)
else:
value = self._after_deployed_property_value_of(
resource_logical_id=logical_name_of_resource,
property_name=attribute_name,
)
if value is not None:
return value

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@simonrw simonrw Oct 21, 2025

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suggestion: perhaps consider an early return here - I think it is clearer to return the value found and not continue with the rest of the function implementation.

node_property: NodeProperty | None = self._get_node_property_for(
property_name=attribute_name, node_resource=node_resource
)
if node_property is not None:
# The property is statically defined in the template and its value can be computed.
property_delta = self.visit(node_property)
value = property_delta.before if select_before else property_delta.after
else:
# The property is not statically defined and must therefore be available in
# the properties deployed set.
if select_before:
value = self._before_deployed_property_value_of(
resource_logical_id=logical_name_of_resource,
property_name=attribute_name,
)
else:
value = self._after_deployed_property_value_of(
resource_logical_id=logical_name_of_resource,
property_name=attribute_name,
)

return value

def visit_node_intrinsic_function_fn_get_att(
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