Remove need for Union_init and Union_stop - #2655
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Union instruments previously required a Union_init component placed first
and a Union_stop component placed last. Union_init inlined the shared
union-lib.c header (types) and union-init.c (the global list state,
accessed through COMP_GETPAR3(Union_init, init, ...)); Union_stop inlined
union-suffix.c (the dispatch switch) exactly once, after every
PROCESS_*_DETECTOR macro had already been defined. This made the required
first/last ordering fragile.
cogen now injects that shared front/back automatically, so Union_init and
Union_stop are no longer required. The change is applied to both mcstas and
mcxtrace in lockstep.
Detection
cogen_instr_uses_union() returns true when the instrument contains a
Union_master or Union_master_GPU component (the master is mandatory when any
Union component is used). The shared code is injected only in that case, so
non-union instruments are byte-for-byte unchanged.
Injection (mccode/src/cogen.c.in)
- Front, at the top of cogen_decls (before the SHARE loop): emit
"#define Union 1", then embed_file("union-lib.c") and
embed_file("union-init.c").
- Back, after the SHARE loop: embed_file("union-suffix.c").
- embed_file() is include-once (via the symtab) and searches the system
directory before the component path, so each shared file is emitted
exactly once even when many union components are present.
Shared state (union-init.c, both compilers)
The file-scope globals are renamed to a g_ prefix so they cannot collide
with the component-local pointers of the same name, e.g.
global_process_list -> g_process_list. Each component keeps its local
pointer but sets it to &g_FOO, so all ->, . and * usages (and the
..._master LHS names) are left untouched.
- mcstas: 13 globals (incl. g_surface_list, g_mantid_min_pixel_id)
- mcxtrace: 11 globals (no surface / mantid_min_pixel_id)
Components (mcstas-comps/union, mcxtrace-comps/union)
- Every union .comp now uses &g_FOO instead of
COMP_GETPAR3(Union_init, init, global_FOO); the
"if (_getcomp_index(init) < 0) {...}" guard blocks are removed.
- mcxtrace components no longer %include union-init.c (cogen injects it);
Template_process.comp's bare &global_process_list becomes &g_process_list.
- Int special case: Union_abs_logger_1D_space_event.comp now reads
g_mantid_min_pixel_id directly (no &, cast dropped).
- Function parameters named global_* in SHARE signatures are untouched.
- Union_init.comp / Union_stop.comp are converted to inert no-ops (empty
SHARE/DECLARE/INITIALIZE), so existing .instr files that still place them
compile and run unchanged. The deprecated string init="init" parameter is
kept so old instruments still parse.
Include guards
union-lib.c, union-init.c and union-suffix.c each gained a guard
(UNION_LIB_C / UNION_INIT_C / UNION_SUFFIX_C) in both mcstas and mcxtrace.
Verification
- mcstas mctest passes: old-style instruments (with init/stop) unchanged;
new-style (no init/stop) reproduce the exact detector value (4.55997e-10);
non-union instruments show no injection markers; the dispatch switch is
emitted once with the PROCESS_*_DETECTOR macros defined before it.
- mcxtrace: Geometry_test compiles with the injection and runs to completion
(Union_master initialized, trace saved; no .nxs counts because all
DETECTORs are commented out in that example). Its meshfile mcrun prompt is
pre-existing (the example requires an external torus.STL it does not ship)
and reproduces identically on the unmodified baseline.
Every Union component (except the no-op Union_init/Union_stop) now emits a clear #error when the shared Union library was not injected, which happens when the instrument contains no Union_master / Union_master_GPU. Previously mcstas carried a stale message pointing at the now-optional Union_init component, and mcxtrace silently defined Union so a masterless instrument failed only with cryptic 'incomplete type' errors. Also drop the dead, never-referenced length_to_boundery_fp declaration in Union_master (mcxtrace, missing semicolon) and Union_master_GPU (mcstas).
mads-bertelsen-agentic
marked this pull request as draft
September 11, 2026 15:21
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Free-form text area
Please describe what your PR is adding in terms of features or bugfixes:
This is a suggestion on how to avoid the need for the Union_init and Union_stop components. Today they serve
two functions:
This branch simply does these things in the cogen by checking if a Union_master or Union_master_GPU is in the instrument. This is to avoid more invasive things like tagging all the Union components, but other suggestions for detecting when to trigger including union globals and libraries.
Instruments with Union_init and Union_stop will continue to work, just show deprecation warnings. Instruments that use the init parameter on Union components explicitly will break as that parameter is not available anymore (mcstas-pygen generated instruments might be extra susceptible to this, as all parameters are always specified).
Declaration of use of AI-tools
Development OS / boundary conditions
Please describe what OS you developed and tested your additions on, and if any special dependencies are required:
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
mcdocutility and rendered a reasonable documentation page for the component (please attach as screenshot in comments!)mctestutility to test one or more instruments making use of the component (please attachmcviewtestreport as screenshot in comments)mccode-clangformattool to apply the standard McCode component indentation schememcrun --c-lint"linter" and followed advice to remove most / all warnings that are raisedMy contribution includes patches to an existing instrument file
mcdocutility and rendered a reasonable documentation page for the instrument (please attach as screenshot in comments!)mctestutility to test the instrument (please attachmcviewtestreport as screenshot in comments)mcrun --c-lint"linter" and followed advice to remove most / all warnings that are raisedMy contribution includes a new component file
mcdocutility and rendered a reasonable documentation page for the component (please attach as screenshot in comments!)mccode-clangformattool to apply the standard McCode component indentation schemecontribcomponent categoryMy contribution includes a new instrument file
mcdocutility and rendered a reasonable documentation page for the instrument (please attach as screenshot in comments!)%Example:line to describe expected behaviourmcrun --c-lint"linter" and followed advice to remove most / all warnings that are raisedexampleshierarchy in a folder in the style ofexamples/ESS/New_stuff/New_stuff.instrexamplefolder, but if general use I have placed it in the globaldatafolder.My work touches the code-generator in mccode/src
My work touches / adds to the runtime lib code (.c,.h etc in multiple locations
My PR is meant to fix a specific, existing issue
My contribution contains something else