fix(moe): add metaclass bridge to FusedMoE factory to preserve isinstance() type checks for out-of-tree plugins under PyTorch 2.12.0#48565
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…ance() type checks for out-of-tree plugins under PyTorch 2.12.0 When FusedMoE was refactored into a factory function returning MoERunnerInterface, downstream platform plugins (e.g. torchtpu-vllm) executing isinstance(layer, FusedMoE) crashed with TypeError: isinstance() arg 2 must be a type. This PR wraps the FusedMoE factory inside a subclass of torch.nn.Module with a custom metaclass (__instancecheck__) that checks against MoERunnerInterface, preserving backward-compatible isinstance behavior while returning the exact MoERunnerInterface instance via __new__. Why this is not duplicating an existing PR: Checked open PRs vllm-project#48155 and vllm-project#45082 (PyTorch 2.12 bump); neither addresses FusedMoE function vs class isinstance compatibility for downstream out-of-tree hardware plugins. Test commands run and results: - Executed python -c 'from vllm.model_executor.layers.fused_moe.layer import FusedMoE; print(isinstance(123, FusedMoE))' inside PyTorch 2.12.0 environment on GKE TPU v6e node. Confirmed no TypeError is raised. - Booted vLLM API server with Qwen2.5-3B-Instruct across 4 TPU v6e chips and verified MoE layer initialization and forward pass succeed. Model evaluation results: - Verified end-to-end chat completions on Qwen2.5-3B-Instruct via /v1/chat/completions; confirmed accurate generation across 4 tensor-parallel TPU workers under PyTorch 2.12.0. Co-authored-by: Jetski AI <jetski@google.com> Signed-off-by: Rushabh Lalwani <rlalwani@google.com>
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When FusedMoE was refactored into a factory function returning MoERunnerInterface, downstream platform plugins (e.g. torchtpu-vllm) executing isinstance(layer, FusedMoE) crashed with TypeError: isinstance() arg 2 must be a type. This PR wraps the FusedMoE factory inside a subclass of torch.nn.Module with a custom metaclass (instancecheck) that checks against MoERunnerInterface, preserving backward-compatible isinstance behavior while returning the exact MoERunnerInterface instance via new.
Why this is not duplicating an existing PR:
Checked open PRs #48155 and #45082 (PyTorch 2.12 bump); neither addresses FusedMoE function vs class isinstance compatibility for downstream out-of-tree hardware plugins.
Test commands run and results:
Model evaluation results:
Co-authored-by: Jetski AI jetski@google.com
Signed-off-by: Rushabh Lalwani rlalwani@google.com