Fix rrule for broadcasted over empty Tuple{}#834
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ChrisRackauckas merged 4 commits intoJuliaDiff:mainfrom Feb 11, 2026
Merged
Fix rrule for broadcasted over empty Tuple{}#834ChrisRackauckas merged 4 commits intoJuliaDiff:mainfrom
ChrisRackauckas merged 4 commits intoJuliaDiff:mainfrom
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When broadcasting over an empty tuple, `Broadcast.combine_eltypes` returns
`Union{}`. Since `Union{} <: Number` is true, the code entered
`may_bc_derivatives` which tried to construct `Tuple{Union{}, ...}` and
errored. Fix by treating `Union{}` as a trivial non-differentiable case
alongside `Bool`.
Fixes JuliaDiff#830
Co-Authored-By: Chris Rackauckas <accounts@chrisrackauckas.com>
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
devmotion
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Feb 11, 2026
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Is it possible to also come up with an example with more arguments?
Co-authored-by: David Müller-Widmann <devmotion@users.noreply.github.com>
Co-authored-by: David Müller-Widmann <devmotion@users.noreply.github.com>
Test atan.((), ()) to cover the multi-arg path through the trivial
broadcast rrule when eltype is Union{}.
Co-Authored-By: Chris Rackauckas <accounts@chrisrackauckas.com>
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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How about that? |
devmotion
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Feb 11, 2026
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Summary
rruleforBroadcast.broadcastedcrashing when broadcasting over an emptyTuple{}(e.g.isone.(()))argscontains an empty tuple,Broadcast.combine_eltypes(f, args)returnsUnion{}. SinceUnion{} <: Numberistrue, the code enteredmay_bc_derivativeswhich tried to constructTuple{Union{}, ...}and errored with "Tuple field type cannot be Union{}"T === Union{}as a trivial non-differentiable case alongsideT === Bool, since empty containers produce empty results with zero gradientsisoneandsinbroadcasted over()Fixes #830
Test plan
Pkg.test(; test_args=["broadcast"])) - all 2679 tests passisone,sin) over empty tuple🤖 Generated with Claude Code