union system updated for McXtrace 3

[ebknudsen]

Including new Compton and Powder scattering process

Free-form text area

Please describe what your PR is adding in terms of features or bugfixes:

This PR adds work done for HALO-Xray in terms of implementing the Union system also for McXtrace 3 and include Compton and Powder scattering processes.

It is currently in a draft stage (i.e. not cleared for merge), using the old Union structure with Geometry_functions.c etc. in separate files. This is intended to be merged into a union-lib.c style description.

---

Development OS / boundary conditions

Please describe what OS you developed and tested your additions on, and if any special dependencies are required:
Debian buster

---

PR Checklist for contributing to McStas/McXtrace

For a coherent and useful contribution to McStas/McXtrace, please fill in relevant parts of the checklist:

• My contribution includes patches to an existing component file

  • I have used the mcdoc utility and rendered a reasonable documentation page for the component (please attach as screenshot in comments!)
  • I have ensured that basic use of the component is OK (e.g. an instrument using it compiles?)
  • I have used the mctest utility to test one or more instruments making use of the component (please attach mcviewtest report as screenshot in comments)
  • I have used the mcrun --c-lint "linter" and followed advice to remove most / all warnings that are raised

• My contribution includes patches to an existing instrument file

  • I have used the mcdoc utility and rendered a reasonable documentation page for the instrument (please attach as screenshot in comments!)
  • I have used the mctest utility to test the instrument (please attach mcviewtest report as screenshot in comments)
  • I have used the mcrun --c-lint "linter" and followed advice to remove most / all warnings that are raised

• My contribution includes a new component file

  • I have ensured that naming of parameters are in the style of existing components. (Please check the McStas or McXtrace NOMENCLATURE docs.)
  • I have ensured that component parameters are in the usually units of McStas or McXtrace (SI + neutron/x-ray 'usual' units)
  • I have used the mcdoc utility and rendered a reasonable documentation page for the component (please attach as screenshot in comments!)
  • I have ensured that basic use of the component is OK (e.g. an instrument using it compiles?)
  • I have included a corresponding example instrument and will fill in the new instrument section below
  • My new component is added within the contrib component category

• My contribution includes a new instrument file

  • I have used the mcdoc utility and rendered a reasonable documentation page for the instrument (please attach as screenshot in comments!)
  • I have ensured that basic use of the instrument is OK (e.g. it compiles?)
  • ... and provided reasonable default parameters in that instrument that produce reasonable output
  • ... and maybe even added a %Example: line to describe expected behaviour
  • I have used the mcrun --c-lint "linter" and followed advice to remove most / all warnings that are raised
  • My new instrument is added within the examples hierarchy in a folder in the style of examples/ESS/New_stuff/New_stuff.instr
  • My new instrument has a new, unique filename, not clashing with existing example instruments
  • My new instrument requires a data/input file. If the datafile is specific for my instrument I have left it in the same example folder, but if general use I have placed it in the global data folder.

• My work touches the code-generator in mccode/src

  • I have added reasoning and documentation for the change through an ADR record in our GRAMMAR section
  • I am attaching test output in the comments

• My work touches / adds to the runtime lib code (.c,.h etc in multiple locations

  • I am have added reasoning and documentation for the change below
  • I am attaching test output in the comments

• My PR is meant to fix a specific, existing issue

  • I have indicated the issue number here:
  • I have added documentation for the fix and possible side effects

• My contribution contains something else

  • Explanation is added in free form text above or below the checklist

---

[ebknudsen]

also this description does not yet contain surface refraction

[willend]

@ebknudsen great, thanks! As discussed elsewhere I will see if I can merge / cut / paste / add some of the improvements from the neutron side later. (Will very likely not happen this side of new years...)

[ebknudsen]

@willend Thanks - this will come at its own pace. Remaining to be done:

1. real regression test instrument(s)
2. adding in the malloc protections in union-lib
3. switching over to union-lib description.
   ... other things that I can't think of right now

In the longer term it could be desirable to split union-lib into a common and a neutron/X-ray specific description, to avoid falling out of sync, but that's not for now/this PR

[willend]

Agree on all of the above