NeXus File Handling Consolidation

[martyngigg]

Summary

Consolidate NeXus file access into a single layer within the codebase. A prompt for this work is the freeze/deprecation of the NeXus code bindings by the standards committee. This is related to the fact that nexus API had its last release in September 2016 and has had no changes since January 2020.

Intended outcome

Mantid currently accesses NeXus files through a variety of mechanisms:

• NeXus C/C++ API
• HDF5 C/C++ API
• Internal NeXus access layer

This spread of methods to access files presents challenges:

• increased maintenance
• confusion for developers
• potential for bugs to my repeated in near duplicate code
• all modern files are HDF5 and the indirect layers such as our own or NeXus provide performance bottlenecks

The benefits of addressing these issues are focused around decreasing the maintenance burden and mental overhead for developers. It is likely we would be able to address performance issues in certain areas too.

Acceptance criteria

A document should be produced describing first the issues with the current solution in more detail followed by the requirements and scope of the solution to be designed to address the problems.