Predeclaration of subdomainIDs with GeneratedMeshGenerator

[rnpratoori]

I have the following mesh block -

[Mesh]
    [2d]
        # generate a 2D mesh
        type = GeneratedMeshGenerator
        dim = 2
        nx = ${nx}
        ny = ${ny}
        xmax = ${dx}
        ymax = ${dy}
        add_subdomain_ids = '0  1   2'
    []
    # Subdomain for ramp
    [c3_domain]
        type = ParsedSubdomainMeshGenerator
        block_id = 2
        combinatorial_geometry = 'y > 1'
        input = 2d
    []
[]
[MeshModifiers]
  [void]
    type = CoupledVarThresholdElementSubdomainModifier
    coupled_var = eta
    criterion_type = ABOVE
    subdomain_id = 1
    threshold = 1e-6
    execute_on = 'INITIAL'
  []
[]

I want to create 2 subdomains from the starting rectangle mesh (2d). One subdomain is based on geometry and I use ParsedSubdomainMeshGenerator. For the other, I want to use CoupledVarThresholdElementSubdomainModifier. This gives me an error that - the following blocks (ids) do not exist on the mesh: 1. Blocks names (resp. ids) that do exist: , (0, 2).

I believe this is because, there is no add_subdomains_ids in GeneratedMeshGenerator. I can't use GeneratedMesh as I cannot use nested mesh object to create subdomain using ParsedSubdomainMeshGenerator.

[GiudGiud]

Hello

You can do

[Mesh]
  add_subdomain_ids = '1'
  [2d]
        # generate a 2D mesh
        type = GeneratedMeshGenerator
        dim = 2
        nx = ${nx}
        ny = ${ny}
  ...