Consistent support of setting the origin in meshes

[j-bowhay]

Describe the current issue

RectangleMesh is unique in that is has originX and originY arguments however many other meshes (e.g. SquareMesh, CubeMesh) don't.

Describe the solution you'd like

It would be convenient if other meshes also supported this consistently.

Describe alternatives you've considered

Just calling TensorBoxMesh etc directly.

Additional info

I completely understand if you don't want to grow the surface area of the api but I though I would raise this as a matter of consistency.

[connorjward]

This is a good idea. I see no reason to not have these. The changes are backwards compatible which is a plus.

[j-bowhay]

@connorjward what is Firedrakes backwards compatibility policy? I see c17ce3e which introduced originX and originY put the argument after Ly but before quadrilateral which would break anyone's code who was passing quadrilateral as a positional argument. I assume any new originX etc arguments would have to go at the end of the signature to ensure backwards compatibility?

[connorjward]

That's an excellent point and something that we haven't really considered. I think that we should be using keyword-only arguments much more extensively through the codebase and here is a great example. I'll bring this to the meeting this week and see what the team say.

[connorjward]

I think users are very unlikely to be using positional arguments for the many many arguments the utility meshes expose. That's why I made my comment about backwards compatibility.

[connorjward]

I'll bring this to the meeting this week and see what the team say.

Actually I think that this is fine. This change can be accomplished in accordance with our deprecation policy. It'll end up being quite verbose but you could have something like:

def UnitSquareMesh(
    nx,
    ny,
    *args,
    reorder=None,
    diagonal="left",
    quadrilateral=False,
    distribution_parameters=None,
    comm=COMM_WORLD,
    name=DEFAULT_MESH_NAME,
    distribution_name=None,
    permutation_name=None,
):
    if args:
        warn("No longer!")
        reorder = args[0]
        if len(args) > 2:  # awful style but this is the concept
            diagonal = args[1]
        ...

We can then remove it all after the next major release.

[connorjward]

In the meeting today we agreed that we should move to keyword-only arguments for most of the arguments for the utility meshes. So my deprecation suggestion is a go.