unxt 2.0.1 makes `ty` report phantom `missing-argument` errors in downstream dataclass constructors

[nstarman]

Upgrading unxt 2.0.0 → 2.0.1 (no other change) makes ty emit 13 false missing-argument errors in coordinax, failing its type-check gate. Runtime is unaffected — the full test suite passes.

Reproduction

In coordinax at 2680b1a (pristine, no source change), bump only the unxt floor:

-  "unxt>=2.0",
+  "unxt>=2.0.1",

$ uv run ty check .
src/coordinax/vectors/_src/point.py:206:12: error[missing-argument] No argument provided for required parameter `rep`
src/coordinax/vectors/_src/point.py:239:12: ...
src/coordinax/vectors/_src/point.py:273:12: ...
src/coordinax/vectors/_src/point.py:304:12: ...
src/coordinax/vectors/_src/register_cx.py:361:12: ...
src/coordinax/vectors/_src/tangent.py:198:12: ...
packages/coordinaxs.interop.astropy/.../frames.py:344:14: ...
packages/coordinaxs.interop.astropy/.../vec_constructors.py:  (5 sites)
packages/coordinaxs.interop.astropy/.../vec_converters.py:388:12: error[missing-argument] No arguments provided for required parameters `basis`, `semantic`

With unxt==2.0.0 the same tree reports 6 diagnostics, all warnings, and the gate passes.

The errors are wrong

The flagged call is

return cls(data=data, chart=chart)

and Point has no rep field at all:

>>> [f.name for f in dataclasses.fields(cxv.Point)]
['data', 'chart', 'frame']

data and chart have no default, frame does. So the call is complete, and rep is not a constructor parameter. Every test passes on 2.0.1 — this is inference, not behaviour.

Likely cause

2.0.1 backports #816 (adopt quax-blocks v5 __make__ for unchecked quantity construction, PR #817), which changes how the unchecked constructor is attached:

src/unxt/_src/quantity/base.py:199
    _mk = quax_blocks.SupportsUncheckedMake.__dict__["__make__"]

That appears to change the __init__ signature ty synthesises for downstream subclasses of the affected bases.

Why it matters now

This blocks the ustrip work from #880. The chain is:

1. unxts.linalg 2.0.4 ships the new ustrip/unit_of dispatches — the thing downstream wants.
2. 2.0.4 calls QuantityMatrix._mk, which needs unxt >= 2.0.1 (its declared unxt>=2.0.0 floor is wrong — unxts.linalg 2.0.4 is unusable with any released unxt: QuantityMatrix._mk does not exist #886).
3. unxt 2.0.1 fails coordinax's ty gate with the phantom errors above.

So there is currently no combination that gives a downstream user the new ustrip and a passing type-check. Reverted the pins in GalacticDynamics/coordinax#716 pending this.

[nstarman]

Closing this — it is resolved, and on reflection it was filed against the wrong project.

Resolved. The 13 errors were all one cause: coordinax's AbstractVector.rep was declared as an equinox.AbstractVar. To a type checker that is Annotated[T, "AbstractVar"], indistinguishable from a real field, so dataclass_transform counted it in the synthesised __init__ and demanded it at every construction site. GalacticDynamics/coordinax#725 fixed it at the root by making rep a derived abstract property — subclasses compute it rather than store it, so it was never an __init__ parameter. GalacticDynamics/coordinax#747 then removed the [[tool.ty.overrides]] blocks that had been added to suppress the symptom.

Verified on current coordinax main with the toolchain that produces the errors — quax 0.4.3, quax-blocks 0.5.0, unxt 2.0.2, jax 0.10.0, ty 0.0.34:

$ uv run ty check | grep -cE "missing-argument|unknown-argument"
0

Wrong project. unxt 2.0.1 did not introduce this; it only raised the quax floor to >=0.4.2, and quax 0.4.2 is where the metaclass __call__ went from -> Any to type[_T] -> _T and stopped erasing the synthesised constructor signature. That change is correct — it is what made these constructor calls checkable at all. The remaining upstream gap is equinox's, that AbstractVar cannot be expressed statically as "not a field": patrick-kidger/equinox#1256.

So there is nothing for unxt to do here. Anyone landing on this from a downstream missing-argument break: the fix is to derive the attribute rather than declare it AbstractVar, not to suppress the rule.