moreniius parity¶

Historical

The code this page audits has since been removed. niess converted McCode instruments to NeXus by reading the emitted instrument back; it converts niess instruments by reading the object tree, and once every target did that, the instrument-reading route was two thousand lines of reconstructing what the tree states. It went with the McStas demotion.

This page is kept as the record of the port, because the port is why the NeXus output looks the way it does, and because the classification of differences below is still the argument for each of them. The module paths named here no longer exist. Nothing in niess reads a .instr to convert it — niess.io.mccode.load_instr still parses one so its placements can be inspected, which is a different thing.

niess replaced moreniius, which converted McCode instruments to ESS NeXus Structure JSON through a nexusformat object model. This page records what happened to every part of it, so nothing was lost silently.

The module paths below were relative to niess/nexus/via_instr/, the subpackage that held the instrument-reading route.

The regression baseline that pins the two against each other, and the classification of every remaining difference, is documented in the golden baseline notes.

Audit¶

Every public piece of moreniius (13 modules, ~2200 lines), and where it went. Nothing is left unaccounted for: each entry is ported, subsumed (the need disappeared with nexusformat), or dropped with a reason.

moreniius itself is untouched and still installable; retiring the repository is a separate, human step.

Ported¶

moreniius	where it went (since removed)	Notes
`mccode/orientation.py` — `NXPart`, `NXParts`, `NXOrient`	`orientation.py`	Same algebra, emitting transformation dicts instead of `NXfield`s
`mccode/instr.py` — `make_transformations`, `resolve_target`, `build_graph`, `inputs`/`outputs`, `guess_origin`, `to_nx`	`instrument.py::NexusContext`	`guess_origin` → `_find_origin`; `to_nx` → the `mcstas` dataset
`mccode/instr.py::expr2nx`	`expression.py::resolve` + `parameter_node`	Split into "decide" and "build"; returns a typed result rather than four unrelated shapes
`mccode/instance.py` — two-tier dispatch, `register_translator`	`registry.py` over `niess.dispatch.NiessRegistry`	Now three tiers (niess source type → niess role → McCode type); shared with `niess.brep`. Where `register_translator` mutated one global table, a registry may instead extend another via `parent=`, so instrument-specific translators are chosen per conversion with `to_nexus_structure(registry=...)` rather than by whatever the process imported
`mccode/instance.py` — `COMPONENT_*_TO_NEXUS`, `get_nx_type`	`instrument.py` — same maps, `default_nx_class`
`mccode/instance.py` — `NEXUS_TO_COMPONENT`	`instrument.py::NEXUS_CLASS_PARAMETERS` + `fallback_body`	Only `NXfermi_chopper` ever populated anything; the other three entries mapped to `{}`
`mccode/comp.py` — `slit`, `guide`, `collimator_linear`, `diskchopper`, `elliptic_guide_gravity`, `monitor` translators	`translators.py`
`additions.py` — `monochromator_rowland_translator`, `detector_tubes_offsets_and_one_cylinder`, `bifrost_detector_collector`, `Frame_monitor`, pixel/`WHEN` helpers	`bifrost.py`, on its own `BIFROST_REGISTRY`	The `ESS_butterfly` → `NXmoderator` mapping went to the generic table in `instrument.py` instead: `niess.components.moderator.ESSModerator` emits it for every instrument, not just BIFROST
`utils.py` — `ess_flatbuffer_specifier`, `ev44_event_data_group`, `link_specifier`, `nxlog_data_links`, `linked_nxlog`	`streams.py`	Minus `NotNXdict`
`utils.py::outer_transform_dependency`	`instrument.py`	Reads `depends_on` from node attributes
`writer.py::convert_types`	`nodes.py::convert_type`	Minus the `NXattr`/`NXfield` branches
`writer.py::_to_absolute`	`nodes.py::to_absolute` + `absolutize_depends_on`	The recursive rewrite is now its own pass rather than part of serialization
`nxoff.py` — `NXoff.from_wedge`, `to_nexus`	`components/geometry.py::Off`	Geometry is a property of the component, not of the NeXus target, so it sits with the components and each target renders it. `sphere` came across with no caller and has not been carried over
`nexus_structure.py` — `load_instr`	`io/mccode.py`	Reading a file survives; see below for `convert`. It is not a NeXus concern, so it lives with the other McCode readers rather than under `nexus/`
`MorEniius.from_mccode` / `to_nexus_structure`	`to_nexus_structure(instr, ...)`	One function; there was never a reason for the two-stage object

Subsumed — the need disappeared with `nexusformat`¶

moreniius	Why it is gone
`utils.NotNXdict`	Existed only to smuggle raw dicts through `NXfield`. Nothing to smuggle through now.
`writer.Writer` and `_to_json_dict`	The tree-walk that turned `nexusformat` objects into JSON. Translators build the JSON directly.
`utils.resolve_parameter_links`	Renamed a link's `config.name` after the fact. `parameter_node` names links correctly when it builds them.
`mccode/instance.NXInstance.make_nx`	Wrapped values in `NXfield`s. Also the source of the group-flattening bug documented in `tests/data/bifrost_nexus_structure_golden.md`.
`utils.dict2NXobj`, `_sanitize`	Rebuilt `nexusformat` objects from JSON blobs.
`only_nx` flag (threaded through nearly every function)	Meant "raise if a non-NeXus object is in the tree". There is no object tree.

Dropped, deliberately¶

moreniius	Reason
`additions.readout_translator` and `BIFROST_DETECTOR_MODULES`	The translator's registration is commented out in `additions.py`, so the module-level cache was written on every detector translation and never read. Reviving it needs the `Readout` component to exist in an instrument first.
`additions.detector_tubes_only_cylinder`	Unregistered alternative giving each pixel its own cylinder. The registered variant (one shared cylinder plus per-pixel offsets) is ported.
`additions.bifrost_pixel_regex_20230703`	Superseded by the `..._20230911` variant, which is the one used.
`mccode/instr.py` `CTargetVisitor` re-run	Unnecessary and wrong — see `variables.py`. Replaced by parsing `Instr.declare` directly, which also fixes the DECLARE folding bug.
`NXInstance.dump_mcstas`	Debug flag, default off, never set by anything.
`utils.get_mcstasscript_component_eniius_data`, `decode_component_eniius_data`, `mccode_component_eniius_data`	The legacy `eniius_data` escape hatch: a JSON blob under METADATA name `eniius_data`/mimetype `json`, or scraped out of an EXTEND block with a regex. niess never used it (only a stale TODO in `components/monitors.py` mentioned it), and `nexus_structure_stream_data` supersedes it for the streaming case it was mostly used for. If a non-niess instrument ever needs arbitrary extra NeXus content per component, add it as a fourth tier in `streams.resolve_stream` rather than reviving the EXTEND-block regex.
`nxoff.NXoff.from_nexus`, `get_guide_params`, `_get_width_height`	Read geometry back out of NeXus; no consumer in the conversion path.
`path_navigator.NexusStructureNavigator`	A reader for navigating finished NeXus Structure JSON — a consumer-side convenience, not conversion. `nodes.find_child` / `nodes.get_attribute` cover what the tests need. Worth porting properly if users want it.
`Writer.to_json`	Wrote the structure to a file. Callers hold a plain dict and can `json.dump` it.
`nexus_structure.convert` — the `instr2ns` script	Removed. It translated an instrument niess did not build, which meant every target carried a second front-end forever. niess translates niess instruments; a `.instr` is not the source of truth in a niess world. `load_instr` survives for reading a file — see Translate a McStas `.instr`, which is the migration story this served.

Dependencies¶

niess never depended on moreniius, so there is nothing to remove from its pyproject.toml — the dependency ran the other way, via moreniius's [project.optional-dependencies] test = [..., 'niess', ...]. Retiring moreniius also retires its nexusformat, networkx, zenlog and platformdirs requirements; niess already had networkx of its own and needs none of the others for this work.