Add submodule mpi

[wdeconinck]

This pull request introduces a new atlas4py.mpi Python submodule, providing comprehensive MPI communicator management from eckit and interoperability with mpi4py and other MPI libraries. It includes the C++ implementation, Python bindings, CMake integration, version parsing utilities, and extensive test coverage. The changes are grouped below by theme.

---

New MPI Python Submodule and Bindings

• Added a new mpi submodule to atlas4py, exposing MPI communicator management, registration, and context management in Python, with support for interoperability with mpi4py and handling communicators as integer handles or objects.

CMake Integration and Version Utilities

• Introduced a reusable CMake function (lifted from ecbuild) and helper file for parsing version strings and exporting version components as variables, including an integer encoding for version comparison (src/atlas4py/cmake/atlas4py_parse_version.cmake). This is needed for ensuring forward/backward compatibility with different atlas versions for an API change.
• Updated the main CMake configuration to build and link the new MPI submodule, include source directories, and propagate version information for conditional compilation (src/atlas4py/CMakeLists.txt).

Testing

• Added comprehensive tests for all new MPI submodule features, including communicator creation, registration, conversion to/from integers and mpi4py, context management with Scope, and communicator splitting (tests/test_bindings.py).

---

These changes provide robust MPI support in atlas4py, enable seamless integration with existing Python MPI workflows, and ensure correctness and maintainability through improved build tooling and thorough testing.

[Copilot]

Pull request overview

Adds MPI communicator management and interoperability to the atlas4py Python bindings.

Changes:

• Adds communicator bindings, registration, scoping, splitting, and mpi4py conversion.
• Adds Atlas version parsing and conditional compilation support.
• Adds MPI binding tests.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
tests/test_bindings.py	Tests MPI APIs and interoperability.
src/atlas4py/mpi/_mpi.hpp	Declares MPI wrappers.
src/atlas4py/mpi/_mpi.cpp	Implements and binds MPI functionality.
src/atlas4py/CMakeLists.txt	Builds the MPI binding sources.
src/atlas4py/cmake/atlas4py_parse_version.cmake	Parses version components.
src/atlas4py/cmake/atlas4py_add_atlas.cmake	Integrates Atlas version detection.
src/atlas4py/_atlas4py.cpp	Registers the MPI submodule.

Suppressed comments (1)

tests/test_bindings.py:497

• The repository runs this suite with plain pytest and has no mpiexec/mpirun test invocation, so world.size is one and color is always zero here. The test only covers the degenerate serial split and cannot detect multi-rank grouping/collective failures. Add an MPI-launched multi-process case with ranks assigned to both colors.

    color = world.rank % 2
    split_comm = world.split(color, "split_comm")

---

💡 Add a code-review agent skill or configure MCP servers for context-aware, tailored reviews. Learn more in the docs.