Support recursive unions in Python servers - #4770
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August 6, 2026 20:56
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Motivation and Context
Smithy recursive-shape boxing correctly adds indirection to direct structure/union cycles, but Python server generation only provides PyO3 conversions for boxed structures. When the cycle requires a
Box<Union>, generated PyO3 methods fail to compile because that type implements neitherFromPyObjectnorIntoPy<PyObject>.Description
Extract the existing boxed-shape PyO3 conversions into a shared renderer and use it for both structures and unions. Boxed union conversion delegates through the union's existing unboxed conversion, preserving the generated Python union representation.
The regression test models a
NativeValueunion andArrayValuestructure that recurse directly through a required member. It generates and compiles the Python server, constructs the recursive value from Python, exercises the boxed getter, and extracts the result back into Rust.Testing
:codegen-server:codegen-server-python:test --tests '*PythonServerUnionGeneratorTest'