Fix a JET error regarding the existence of the local variable reducer at a certain point#169
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DilumAluthge merged 3 commits intomasterfrom Feb 21, 2026
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…r` at a certain point ``` ┌ var"@distributed"(__source__::LineNumberNode, __module__::Module, args::Vararg{Any}) @ Distributed /workpath/Distributed.jl/src/macros.jl:363 │ local variable `reducer` may be undefined: reducer::Any └──────────────────── ``` By the time we get to this location in the code, we know that the local variable `reducer` exists, by the following reasoning. If the number of arguments is 1, then we have already returned before this point. If the number of arguments is neither 1 nor 2, then we have already thrown an exception by this point. Thus, if we reach this line, the number of arguments must be 2. Since the number of arguments is 2, we know that we executed the `reducer = args[1]` line above, which means that `reducer` is defined. (cherry picked from commit cdb1106)
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JamesWrigley
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Feb 20, 2026
src/macros.jl
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| ref | ||
| end | ||
| else | ||
| @assert @isdefined reducer # Fixes a JET warning |
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Nitpicking, I dislike this kind of control-flow where variables are only sometimes created. I would prefer initializing reducer to e.g. identity and removing the assert.
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Alright, we now initialize reducer = identity in the na == 1 branch.
And I manually confirmed that this still fixes the JET error.
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…r` at a certain point (#169) This is a forward-port of JuliaLang/Distributed.jl#169 (JuliaLang/Distributed.jl@1bc91f9). ``` ┌ var"@distributed"(__source__::LineNumberNode, __module__::Module, args::Vararg{Any}) @ Distributed /workpath/Distributed.jl/src/macros.jl:363 │ local variable `reducer` may be undefined: reducer::Any └──────────────────── ``` (cherry picked from commit 1bc91f97a75c1ac321ed28dfca072cbabfad7b4c)
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In the
na == 1branch, we just definereducer = identity.Old PR description:
By the time we get to this location in the code, we know that the local variablereducerexists, by the following reasoning. If the number of arguments is 1, then we have already returned before this point. If the number of arguments is neither 1 nor 2, then we have already thrown an exception by this point. Thus, if we reach this line, the number of arguments must be 2. Since the number of arguments is 2, we know that we executed thereducer = args[1]line above, which means thatreduceris defined.