"bad line xxx of yyy.nl file" error with AmplNLWriter (but solves with Ipopt.jl)

Specific Domains Optimization (Mathematical)
4

It’s a bug in the MOI.FileFormats.NL: FileFormats.NL does not support univariate OPMULT · Issue #1886 · jump-dev/MathOptInterface.jl · GitHub.

We don’t handle prod with a single element correctly.

Here’s the minimal reproducer:

using JuMP
import AmplNLWriter
import Ipopt_jll

function main()
    model = Model(() -> AmplNLWriter.Optimizer(Ipopt_jll.amplexe))
    @variable(model, x)
    @NLobjective(model, Min, prod(x for j=1:1))
    optimize!(model)
    return
end

main()
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