[finsberg]

Summary

write_mesh and write_function get an on_input_mesh: bool = False argument, the same as write_meshtags, write_cell_data and write_point_data already have. Writing everything in the input ordering is now one flag on every call:

io4dolfinx.write_mesh(filename, mesh, on_input_mesh=True)
io4dolfinx.write_function(filename, u, on_input_mesh=True)
io4dolfinx.write_meshtags(filename, mesh, tags, on_input_mesh=True)
io4dolfinx.write_cell_data(filename, f0, 0.0, mode, args, backend, on_input_mesh=True)

Before, the mesh and function needed separate functions (write_mesh_input_order, write_function_on_input_mesh), while tags and data used a flag.

Changes

• write_mesh(..., on_input_mesh=True) builds the mesh data with create_original_mesh_data, and write_function(..., on_input_mesh=True) builds the function data with create_function_data_on_original_mesh. These are the same builders the old functions use. mesh_name now works in both orderings.
• write_mesh(..., on_input_mesh=True, store_partition_info=True) raises a ValueError, because partition info has no meaning for a mesh in the input ordering.
• Deprecation: write_mesh_input_order and write_function_on_input_mesh keep their signatures and are still exported from io4dolfinx. They now call the new keyword and emit a DeprecationWarning, following the pattern of reconstruct_mesh.
• The old functions moved from original_checkpoint.py to checkpointing.py, to avoid a circular import. original_checkpoint.py keeps the data builders. Only code that imports the old functions from io4dolfinx.original_checkpoint directly is affected; nothing in the repo does.
• Tests, docs (quickstart, input-order tutorial, openCARP backend) and docstrings now use the new keyword.

Testing

• The existing original-checkpoint tests, which run under MPI through ipyparallel, now use write_mesh/write_function with on_input_mesh=True, and pass.
• The openCARP tests write the mesh with write_mesh(on_input_mesh=...) in both orderings, and pass serially and on 3 ranks.
• Checked by hand:
  • the old and new calls write byte-identical files;
  • the deprecation warnings point at the caller's line;
  • store_partition_info=True with on_input_mesh=True raises.
• Full suite: 2646 passed. The 4 failures in test_legacy_readers.py also fail without these changes and come from the local legacy data. ruff and mypy pass.

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