Declined proposal: quantity-valued coordinates / coord_units for evaluate()

Status: Declined — maintainer ruling D7, 2026-07-06 (units-family scope decision, docs/reviews/2026-07/REMEDIATION-WORKLIST.md). Recorded here so the idea is findable if it is ever revisited; the placeholder tests that used to stand in for it were deleted (LE-08, LE-10, LE-11 / WA-23, WA-24).

What was proposed

A family of unit-aware coordinate conveniences, which existed only as skipped test placeholders (never implemented, no design doc):

  1. coord_units= parameter for uw.function.evaluate() — interpret a plain coordinate array in a named unit, e.g. evaluate(T.sym, pts_km, coord_units="km").

  2. Quantity-valued coordinate lists — accept [(uw.quantity(0.5, "m"), uw.quantity(50, "cm"))] (and flat [x_qty, y_qty]) as evaluate/global_evaluate coordinates.

  3. UnitAwareArray returns from coordinate-expression evaluation, and Pint-quantity coordinate support in mesh.points_in_domain() / mesh.get_closest_cells().

  4. Constructor-set mesh units — units= on the Cartesian mesh constructors as a live feature, plus mesh.to_units() conversion.

The ruling

The family is unsupported. The model owns the unit system (docs/developer/design/UNITS_SIMPLIFIED_DESIGN_2025-11.md): coordinates passed to evaluation are plain arrays in model (non-dimensional) units, or whole UnitAwareArray/UWQuantity arrays (which the evaluate gateway non-dimensionalises). Physical locations are converted explicitly with uw.scaling.non_dimensionalise. The mesh-constructor units= kwarg is deprecated (DeprecationWarning) and ignored; mesh.units reports the model’s coordinate unit.

What was removed (Wave A, 2026-07)

  • 16 placeholder skips across 7 units test files (test_0730, test_0800_unit_aware_functions, test_0803_* ×2, test_0804, test_0811); files that contained nothing else were deleted.

  • test_0630_mesh_units_demonstration.py (pure demonstration of the superseded proposal); test_0620_mesh_units_interface.py rewritten to assert the implemented model-owned semantics.

  • test_0812_poisson_with_units.py rewritten with supported coordinate forms (the Poisson-with-units coverage is regained).

If the feature is revisited, start from the deleted tests in git history — they are a usable statement of the intended user experience.