DM-37534: Ensure that pex_exceptions is imported for afw.fits

[timj]

Without this it is not possible to "import lsst.afw.fits" because the FitsError is not translated to python. Tests passed in afw because other parts of afw were importing pex_exceptions.

[timj]

This is the error without this change:

Traceback:
../../miniconda/envs/lsst-scipipe-5.0.0/lib/python3.10/importlib/__init__.py:126: in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
python/lsst/obs/base/__init__.py:22: in <module>
    from ._fitsRawFormatterBase import *
python/lsst/obs/base/_fitsRawFormatterBase.py:27: in <module>
    import lsst.afw.fits
../../stack/lsst-scipipe-5.0.0/Darwin/afw/g87b8406481+bd7147d3c6/python/lsst/afw/fits/__init__.py:22: in <module>
    from ._fits import *
E   ImportError: generic_type: type "FitsError" referenced unknown base type "lsst::pex::exceptions::IoError"

@mwittgen I was under the impression that this line https://github.com/lsst/afw/blob/main/python/lsst/afw/fits/_fits.cc#L286 means that the python import was not needed. Seems I was wrong.

[timj]

Looking at the code, we currently have explicit mentions of lsst.pex.exceptions in 5 places so we don't seem to attempt to always ensure that it's imported when we have defined a C++ exception. In lsst.afw.fits we have:

wrappers.addSignatureDependency("lsst.pex.exceptions");

and that doesn't seem to have the effect of importing pex_exceptions. In meas_base we have:

py::module::import("lsst.pex.exceptions");

which is explicit about it.

[mwittgen]

afw/python/lsst/afw/fits/_fits.cc

Line 286 in 87b8406

wrappers.addSignatureDependency("lsst.pex.exceptions");

This should be
wrappers.addInheritanceDependency("lsst.pex.exceptions");

The reason is

afw/include/lsst/afw/fits.h

Line 36 in 87b8406

LSST_EXCEPTION_TYPE(FitsError, lsst::pex::exceptions::IoError, lsst::afw::fits::FitsError)

the fitsError class, etc inheriting from lsst::pex::exceptions classes

[timj]

@mwittgen changing does fix the problem. I also fixed afw.geom since that was also trying to export a wrapped exception. Please take another look.

[mwittgen]

Looks good and this is correcting an earlier mistake of mine.