fix[next]: register jax.core.Tracer for embedded field dispatch on jax >= 0.11 - #2867
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…x >= 0.11 common._field / common._connectivity are functools.singledispatch and the embedded JAX backend registers them for jnp.ndarray (== jax.Array). Since jax 0.11, jax.Array is built by ArrayMeta and Tracer is no longer in its MRO; only isinstance() reports it as a jax.Array. singledispatch resolves on the MRO, so constructing a field from a traced array under jit/grad/scan fell through to the base implementation and raised NotImplementedError. Register jax.core.Tracer explicitly; it is a no-op on older jax where Tracer already subclasses jax.Array. Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01HVrnd8v75kACJXMcdNovAN
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September 9, 2026 13:20
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LGTM. Would it make sense to also bump the minimum required version of jax ?
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common._field/common._connectivityarefunctools.singledispatchfunctions; the embedded JAX backend registers them forjnp.ndarray(which isjax.Array). Since jax 0.11jax.Arrayis built by a metaclass (ArrayMeta) andjax.core.Traceris no longer in its MRO; onlyisinstance()still reports a tracer as ajax.Array, viaArrayMeta.__instancecheck__.singledispatchresolves on the class hierarchy, so constructing a field from a traced array (insidejax.jit,jax.grad,jax.lax.scan, ...) falls through to the base implementation and raises a bareNotImplementedError.Fix: additionally register
jax.core.Tracer. On older jax, whereTraceralready subclassesjax.Array, the extra registration resolves to the same implementation and is a no-op.