Can't directly access a sub-subcomponents variables

[AnalogBitTwiddler]

Is your feature request related to a problem? Please describe.

When attempting to make a top level variable that summarizes leaf variables, the leaf variables required duplicating at all intermediate levels.

Describe the solution you’d like

Treat the components of a subcomponent as accessible elements. See commented version below.

Describe alternatives you’ve considered

Workaround is available by introducing intermediate variables at all intermediate levels of hierarchy.

Additional context

using ModelingToolkit  

@mtkmodel AMdl begin
    @description "A Model"
    @variables begin
        a(t)::Float64 = 0
    end
    @equations begin  
        a ~ sin(2π * t / 10) 
    end
end
@mtkmodel Bmdl begin
    @description "B Model"
    @components begin
        a = [AMdl() for i in 1:2]
    end
    @variables begin  # added to show accessing through a variable
        b(t)[1:2]
    end
    @equations begin  # added to show accessing through a variable
        [b[i] ~ a[i].a for i in 1:2]
    end
end
@mtkmodel Cmdl begin
    @description "C Model"
    @components begin
        b = Bmdl()
    end
    @variables begin
        c(t)[1:2]
    end
    @equations begin  
        # [c[i] ~ b.a[i].a for i in 1:2]  # does not work - accessing through a component
        [c[i] ~ b.b[i].a for i in 1:2]  # works - accessing through a variable
    end
end
@mtkbuild cmdl = Cmdl()
observed(cmdl) # Check the observed variables

[cstjean]

Maybe see #2674 (comment) ? Component arrays are sadly not indexable, but you can get around it with getproperty. I agree that it should be fixed though.