MOF broken with new NLP backend

[jd-lara]

After updating to PowerModels 0.21 with the new NL backend. It seems that the mof export broke

I'll update this issue with a minimum example but in the mean time here is the stack trace in case is obvious.

MethodError: no method matching _convert_nonlinear_to_mof(::Type{OrderedDict{String, Any}}, ::MathOptInterface.ScalarQuadraticFunction{Float64}, ::Vector{Any}, ::Dict{MathOptInterface.VariableIndex, String})
│    
│    Closest candidates are:
│      _convert_nonlinear_to_mof(::Type{T}, ::Complex, ::Vector{Any}, ::Dict{MathOptInterface.VariableIndex, String}) where T<:Union{Dict{String, Any}, OrderedDict{String, Any}}
│       @ MathOptInterface ~/.julia/packages/MathOptInterface/3JqTJ/src/FileFormats/MOF/write.jl:270
│      _convert_nonlinear_to_mof(::Type{T}, ::Real, ::Vector{Any}, ::Dict{MathOptInterface.VariableIndex, String}) where T<:Union{Dict{String, Any}, OrderedDict{String, Any}}
│       @ MathOptInterface ~/.julia/packages/MathOptInterface/3JqTJ/src/FileFormats/MOF/write.jl:261
│      _convert_nonlinear_to_mof(::Type{T}, ::MathOptInterface.VariableIndex, ::Vector{Any}, ::Dict{MathOptInterface.VariableIndex, String}) where T<:Union{Dict{String, Any}, OrderedDict{String, Any}}
│       @ MathOptInterface ~/.julia/packages/MathOptInterface/3JqTJ/src/FileFormats/MOF/write.jl:252
│      ...
│    
│    Stacktrace:
│      [1] _convert_nonlinear_to_mof(::Type{OrderedDict{String, Any}}, f::MathOptInterface.ScalarNonlinearFunction, node_list::Vector{Any}, name_map::Dict{MathOptInterface.VariableIndex, String}) (repeats 2 times)
│        @ MathOptInterface.FileFormats.MOF ~/.julia/packages/MathOptInterface/3JqTJ/src/FileFormats/MOF/write.jl:243
│      [2] moi_to_object
│        @ MathOptInterface.FileFormats.MOF ~/.julia/packages/MathOptInterface/3JqTJ/src/FileFormats/MOF/write.jl:295 [inlined]
│      [3] moi_to_object(index::MathOptInterface.ConstraintIndex{MathOptInterface.ScalarNonlinearFunction, MathOptInterface.EqualTo{Float64}}, model::MathOptInterface.Utilities.UniversalFallback{MathOptInterface.Utilities.GenericModel{Float64, MathOptInterface.Utilities.ObjectiveContainer{Float64}, MathOptInterface.Utilities.VariablesContainer{Float64}, MathOptInterface.FileFormats.MOF.InnerModelFunctionConstraints{Float64}}}, name_map::Dict{MathOptInterface.VariableIndex, String})
│        @ MathOptInterface.FileFormats.MOF ~/.julia/packages/MathOptInterface/3JqTJ/src/FileFormats/MOF/write.jl:184
│      [4] write_constraints(object::OrderedDict{String, Any}, model::MathOptInterface.Utilities.UniversalFallback{MathOptInterface.Utilities.GenericModel{Float64, MathOptInterface.Utilities.ObjectiveContainer{Float64}, MathOptInterface.Utilities.VariablesContainer{Float64}, MathOptInterface.FileFormats.MOF.InnerModelFunctionConstraints{Float64}}}, name_map::Dict{MathOptInterface.VariableIndex, String})
│        @ MathOptInterface.FileFormats.MOF ~/.julia/packages/MathOptInterface/3JqTJ/src/FileFormats/MOF/write.jl:143
│      [5] write(io::IOStream, model::MathOptInterface.Utilities.UniversalFallback{MathOptInterface.Utilities.GenericModel{Float64, MathOptInterface.Utilities.ObjectiveContainer{Float64}, MathOptInterface.Utilities.VariablesContainer{Float64}, MathOptInterface.FileFormats.MOF.InnerModelFunctionConstraints{Float64}}})

[odow]

I think it's because we've since allowed ScalarAffineFunction and ScalarQuadraticFunctions as nodes in the graph, which I didn't plan on when I originally wrote this. Let me fix.

[odow]

julia> import MathOptInterface as MOI

julia> model = MOI.FileFormats.MOF.Model()
A MathOptFormat Model

julia> x = MOI.add_variable(model)
MOI.VariableIndex(1)

julia> f = 1.0 * x + 2.0
2.0 + 1.0 MOI.VariableIndex(1)

julia> g = MOI.ScalarNonlinearFunction(:log, Any[f])
log(2.0 + 1.0 MOI.VariableIndex(1))

julia> MOI.set(model, MOI.ObjectiveSense(), MOI.MIN_SENSE)

julia> MOI.set(model, MOI.ObjectiveFunction{typeof(g)}(), g)

julia> MOI.write_to_file(model, "test.mof.json")
ERROR: MethodError: no method matching _convert_nonlinear_to_mof(::Type{OrderedCollections.OrderedDict{String, Any}}, ::MathOptInterface.ScalarAffineFunction{Float64}, ::Vector{Any}, ::Dict{MathOptInterface.VariableIndex, String})

Closest candidates are:
  _convert_nonlinear_to_mof(::Type{T}, ::Complex, ::Vector{Any}, ::Dict{MathOptInterface.VariableIndex, String}) where T<:Union{Dict{String, Any}, OrderedCollections.OrderedDict{String, Any}}
   @ MathOptInterface ~/.julia/packages/MathOptInterface/3JqTJ/src/FileFormats/MOF/write.jl:270
  _convert_nonlinear_to_mof(::Type{T}, ::Real, ::Vector{Any}, ::Dict{MathOptInterface.VariableIndex, String}) where T<:Union{Dict{String, Any}, OrderedCollections.OrderedDict{String, Any}}
   @ MathOptInterface ~/.julia/packages/MathOptInterface/3JqTJ/src/FileFormats/MOF/write.jl:261
  _convert_nonlinear_to_mof(::Type{T}, ::MathOptInterface.VariableIndex, ::Vector{Any}, ::Dict{MathOptInterface.VariableIndex, String}) where T<:Union{Dict{String, Any}, OrderedCollections.OrderedDict{String, Any}}
   @ MathOptInterface ~/.julia/packages/MathOptInterface/3JqTJ/src/FileFormats/MOF/write.jl:252
  ...

Stacktrace:
  [1] _convert_nonlinear_to_mof(::Type{OrderedCollections.OrderedDict{String, Any}}, f::MathOptInterface.ScalarNonlinearFunction, node_list::Vector{Any}, name_map::Dict{MathOptInterface.VariableIndex, String})
    @ MathOptInterface.FileFormats.MOF ~/.julia/packages/MathOptInterface/3JqTJ/src/FileFormats/MOF/write.jl:243
  [2] moi_to_object(foo::MathOptInterface.ScalarNonlinearFunction, name_map::Dict{MathOptInterface.VariableIndex, String})
    @ MathOptInterface.FileFormats.MOF ~/.julia/packages/MathOptInterface/3JqTJ/src/FileFormats/MOF/write.jl:295
  [3] write_objective(object::OrderedCollections.OrderedDict{…}, model::MathOptInterface.Utilities.UniversalFallback{…}, name_map::Dict{…})
    @ MathOptInterface.FileFormats.MOF ~/.julia/packages/MathOptInterface/3JqTJ/src/FileFormats/MOF/write.jl:130
  [4] write(io::IOStream, model::MathOptInterface.Utilities.UniversalFallback{MathOptInterface.Utilities.GenericModel{…}})
    @ MathOptInterface.FileFormats.MOF ~/.julia/packages/MathOptInterface/3JqTJ/src/FileFormats/MOF/write.jl:27
  [5] #9
    @ ~/.julia/packages/MathOptInterface/3JqTJ/src/FileFormats/FileFormats.jl:114 [inlined]
  [6] open(::MathOptInterface.FileFormats.var"#9#10"{MathOptInterface.Utilities.UniversalFallback{MathOptInterface.Utilities.GenericModel{…}}}, ::String, ::Vararg{String}; kwargs::@Kwargs{})
    @ Base ./io.jl:396
  [7] open(::Function, ::String, ::String)
    @ Base ./io.jl:393
  [8] compressed_open(f::Function, filename::String, mode::String, ::MathOptInterface.FileFormats.NoCompression)
    @ MathOptInterface.FileFormats ~/.julia/packages/MathOptInterface/3JqTJ/src/FileFormats/utils.jl:213
  [9] compressed_open(f::Function, filename::String, mode::String, ::MathOptInterface.FileFormats.AutomaticCompression)
    @ MathOptInterface.FileFormats ~/.julia/packages/MathOptInterface/3JqTJ/src/FileFormats/utils.jl:251
 [10] write_to_file(model::MathOptInterface.Utilities.UniversalFallback{MathOptInterface.Utilities.GenericModel{…}}, filename::String)
    @ MathOptInterface.FileFormats ~/.julia/packages/MathOptInterface/3JqTJ/src/FileFormats/FileFormats.jl:113
 [11] top-level scope
    @ REPL[224]:1