using ModelingToolkit
using ModelingToolkit: t_nounits as t, D_nounits as D
using OrdinaryDiffEq
using JuliaSimCompiler
function inner(; a = 0, name)
    @parameters a = a
    @variables x(t) = 0
    ODESystem([D(x) ~ a], t; name)
end

function outer(; name)
    @parameters a = 1
    systems = @named begin
        i = inner(a=a)
    end
    @variables y(t) = 0
    ODESystem([D(y) ~ a], t; name, systems)
end

@named o = outer()
o = complete(o)
prob = ODEProblem(structural_simplify(o), [], (0, 1))
sol = solve(prob, Tsit5())
@assert sol[o.y] ≈ sol[o.i.x]

julia> sol = solve(prob, Tsit5())
ERROR: UndefVarError: `i₊a` not defined
Stacktrace:
...
  [7] (::RuntimeGeneratedFunctions.RuntimeGeneratedFunction{…})(::Vector{…}, ::Vector{…}, ::Vector{…}, ::Float64)
    @ RuntimeGeneratedFunctions ~/.julia/packages/RuntimeGeneratedFunctions/M9ZX8/src/RuntimeGeneratedFunctions.jl:150
  [8] f
    @ ~/.julia/packages/ModelingToolkit/353ne/src/systems/diffeqs/abstractodesystem.jl:343 [inlined]
...

julia> prob.f.f.f_oop
RuntimeGeneratedFunction(#=in ModelingToolkit=#, #=using ModelingToolkit=#, :((ˍ₋arg1, ˍ₋arg2, t)->begin
          begin
              #= /home/fredrikb/.julia/packages/SymbolicUtils/0opve/src/code.jl:468 =#
              (SymbolicUtils.Code.create_array)(typeof(ˍ₋arg1), nothing, Val{1}(), Val{(2,)}(), ˍ₋arg2[1], i₊a)
          end
      end))