Allow interpolation on Distributed architectures (#3499)

* bugfix

* allow interpolation on Distributed

src/Fields/interpolate.jl

@@ -7,6 +7,8 @@ using Oceananigans.Grids: topology, node,
                           ZRegOrthogonalSphericalShellGrid,
                           RectilinearGrid, LatitudeLongitudeGrid
 
+using Oceananigans.Architectures: child_architecture
+
 # GPU-compatile middle point calculation
 @inline middle_point(l, h) = Base.unsafe_trunc(Int, (l + h) / 2)
 
@@ -313,6 +315,12 @@ function interpolate!(to_field::Field, from_field::AbstractField)
 
     to_arch   = architecture(to_field)
     from_arch = architecture(from_field)
+
+    # In case architectures are `Distributed` we 
+    # verify that the fields are on the same child architecture
+    to_arch   = child_architecture(to_arch)
+    from_arch = child_architecture(from_arch)
+
     if !isnothing(from_arch) && to_arch != from_arch
         msg = "Cannot interpolate! because from_field is on $from_arch while to_field is on $to_arch."
         throw(ArgumentError(msg))