Constructing a SphericalRepresentation object with a negative distance is impossible

The explicit kwarg in the error dosen’t seem to work.

In [2]: from astropy.coordinates import Distance, SphericalRepresentation; import astropy.units as u                                                                                                                                 
In [3]: SphericalRepresentation(10*u.deg, 10*u.deg, Distance(-100*u.m, allow_negative=True))    

---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
~/Git/astropy/astropy/coordinates/representation.py in __init__(self, lon, lat, distance, differentials, copy)
   1569             try:
-> 1570                 self._distance = Distance(self._distance, copy=False)
   1571             except ValueError as e:

~/Git/astropy/astropy/coordinates/distances.py in __new__(cls, value, unit, z, cosmology, distmod, parallax, dtype, copy, order, subok, ndmin, allow_negative)
    183         if not allow_negative and np.any(distance.value < 0):
--> 184             raise ValueError("Distance must be >= 0.  Use the argument "
    185                              "'allow_negative=True' to allow negative values.")

ValueError: Distance must be >= 0.  Use the argument 'allow_negative=True' to allow negative values.

During handling of the above exception, another exception occurred:

ValueError                                Traceback (most recent call last)
<ipython-input-3-bc5d4ae3542b> in <module>
----> 1 SphericalRepresentation(10*u.deg, 10*u.deg, Distance(-100*u.m, allow_negative=True))

~/Git/astropy/astropy/coordinates/representation.py in __init__(self, lon, lat, distance, differentials, copy)
   1571             except ValueError as e:
   1572                 if e.args[0].startswith('Distance must be >= 0'):
-> 1573                     raise ValueError("Distance must be >= 0. To allow negative "
   1574                                      "distance values, you must explicitly pass"
   1575                                      " in a `Distance` object with the the "

ValueError: Distance must be >= 0. To allow negative distance values, you must explicitly pass in a `Distance` object with the the argument 'allow_negative=True'.

[astrojuanlu]

This was fixed in #11113:

In [1]: from astropy.coordinates import Distance, SphericalRepresentation; import astropy.units as u

In [2]: SphericalRepresentation(10*u.deg, 10*u.deg, Distance(-100*u.m, allow_negative=True))
Out[2]: 
<SphericalRepresentation (lon, lat, distance) in (deg, deg, m)
    (10., 10., -100.)>

[mhvk]

p.s. Though frankly I’d prefer it if we moved this use of distance out of the representation class altogether, and instead did it inside frames.