Fix spurious KeyReuseError under vmap over a zero-sized key array#38174
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Lawson-Darrow wants to merge 1 commit into
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Fix spurious KeyReuseError under vmap over a zero-sized key array#38174Lawson-Darrow wants to merge 1 commit into
Lawson-Darrow wants to merge 1 commit into
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With jax_debug_key_reuse enabled, vmap over a zero-sized PRNG key array raised a spurious KeyReuseError even when the function did no key reuse. In _SourceSinkBase.__init__ an all-True mask collapses to scalar True, but np.all() is vacuously True for an empty array, so a mask from a zero-sized vmap axis (which affects no keys) wrongly became True, i.e. full consumption. Check `not np.any(mask)` before `np.all(mask)` so an empty mask collapses to False, a no-op.
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This pull request fixes an issue where vmap over a zero-sized key axis raised a spurious KeyReuseError. It reorders the mask checks in jax/experimental/key_reuse/_core.py so that empty masks (where np.all is vacuously True) are correctly handled first as a no-op. A regression test has also been added to verify this behavior. There are no review comments, so I have no additional feedback to provide.
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Fixes #37859.
When
jax_debug_key_reuseis enabled,vmap-ing a function over a zero-sized PRNG key array raised a spuriousKeyReuseError, even when the function did no key reuse (e.g. it split its key and consumed each derived sub-key exactly once).In
_SourceSinkBase.__init__, an all-True mask is collapsed to scalarTrue. Butnp.all()is vacuouslyTruefor an empty array, so a mask coming from a zero-sizedvmapaxis (which affects no keys) was wrongly collapsed toTrue, i.e. full consumption, which then tripped the reuse check.Checking
not np.any(mask)beforenp.all(mask)makes an empty mask collapse toFalse(a no-op) while leaving every non-empty mask unchanged (for any non-empty mask exactly one of the two branches was already taken). Adds a regression test.