Xpress missing _license_probe: licensed_solvers includes xpress with an out-of-date licence, breaking local tests

[FabianHofmann]

Local testing should be stable despite the xpress licence problem.

Note

The following content was generated by AI.

Issue Description

With a local Xpress licence that predates the pip wheel (here: XPAUTH_PATH pointing to a licence valid up to release 9.4, wheel resolves xpress==9.9.1 via the solvers extra), pytest produces ~683 failures, all Xpress. xpress still counts as licensed, so every solver-parametrized test runs it.

Workaround -k "not xpress" is broken as well: it also deselects every test with expression in its name.

Reproducible Example

uv sync --extra dev --extra solvers        # xpress 9.9.1, Python 3.13, Linux
export XPAUTH_PATH=/opt/xpress/xpauth.xpr  # licence valid up to 9.4
uv run python -c "import linopy; print(list(linopy.licensed_solvers)); print(linopy.solvers.check_solver_licenses('xpress'))"
# ['gurobi', 'highs', 'scip', 'cplex', 'xpress']
# {'xpress': LicenseStatus(solver='xpress', ok=True, message=None)}
uv run python -c "import xpress; xpress.init()"
# xpress.InterfaceError: Xpress licensing error 21: Your license only authorizes up to release 9.4. Please contact support@fico.com to upgrade it.

With env -u XPAUTH_PATH the wheel's bundled community licence is used and everything passes, so CI (no XPAUTH_PATH) never hits this.

Root cause

Solver.license_status() / licensed_solvers rely on the per-solver _license_probe hook. Gurobi, Knitro, Mosek, COPT, MindOpt, cuPDLPx and cuOpt implement it; Xpress does not, so the no-op default reports it as licensed. On top of that, most test modules (15 files, e.g. test_io.py, test_sos_*.py, test_infeasibility.py) parametrize over available_solvers (importable only) rather than licensed_solvers like test_optimization.py does.

Expected Behavior / proposed solution

A solver that cannot acquire a licence is not in licensed_solvers, and tests that solve only parametrize over licensed_solvers:

class Xpress(Solver[None]):
    @classmethod
    def _license_probe(cls) -> None:
        xpress.init()

# test modules that actually solve
from linopy import licensed_solvers
@pytest.mark.parametrize("solver", licensed_solvers)

Stays fail-fast and visible: available_solvers keeps its importable-only semantics (no licence at import), the probe error is exposed via check_solver_licenses(), and test_optimization.py already prints the tested solvers in its header.

Alternatives considered:

• Probe the licence in available_solvers: breaks the documented "no licence at import/membership" contract.
• Pin xpress<9.5: pins everyone to an old release to fit one local licence; the community licence covers newer releases.
• Pytest --exclude-solver option: treats the symptom; still reports an unlicensed solver as licensed to users.

Related: mypy

uv run mypy linopy reports 28 errors in linopy/solvers.py when xpress 9.9.1 is installed. The wheel ships py.typed/__init__.pyi, and the flagged lines are mostly the pre-9.8 fallback branches (chgobjsense, addnames, postsolve, getDual, readbasis, xpress.maximize, ...) plus Optional arrays passed to loadMIQP. CI does not see it because the mypy job installs [dev,spec] without solvers. Related to #533.

mypy output (xpress 9.9.1, mypy 2.3.1)

linopy/solvers.py:2730: error: Module has no attribute "maximize"  [attr-defined]
linopy/solvers.py:2755: error: Argument 1 to "enter_context" of "_BaseExitStack" has incompatible type "problem"; expected "AbstractContextManager[Never, bool | None]"  [arg-type]
linopy/solvers.py:2854: error: Argument "objqcol1" to "loadMIQP" of "problem" has incompatible type "ndarray[...] | None"; expected "Iterable[var | int | str]"  [arg-type]
linopy/solvers.py:2876: error: "problem" has no attribute "loadproblem"  [attr-defined]
linopy/solvers.py:2909: error: "problem" has no attribute "chgobjsense"; maybe "chgObjSense"?  [attr-defined]
linopy/solvers.py:2922: error: "problem" has no attribute "addnames"; maybe "addNames"?  [attr-defined]
linopy/solvers.py:3015: error: Argument 1 to "setControl" of "problem" has incompatible type "dict[str, Any]"; expected "dict[str | int, str | float]"  [arg-type]
linopy/solvers.py:3021: error: "problem" has no attribute "setlogfile"; maybe "setLogFile"?  [attr-defined]
linopy/solvers.py:3027: error: "problem" has no attribute "readbasis"; maybe "readBasis"?  [attr-defined]
linopy/solvers.py:3035: error: "problem" has no attribute "postsolve"; maybe "postSolve"?  [attr-defined]
linopy/solvers.py:3042: error: "problem" has no attribute "writebasis"; maybe "writeBasis"?  [attr-defined]
linopy/solvers.py:3051: error: "problem" has no attribute "writebinsol"; maybe "writeBinSol"?  [attr-defined]
linopy/solvers.py:3080: error: "problem" has no attribute "getDual"; maybe "getDuals"?  [attr-defined]
... (28 errors total)

Installed Versions

linopy master / spec-whole-model (0.9.1.post1.dev89), xpress 9.9.1, mypy 2.3.1, Python 3.13.11, Ubuntu 24.04.