BUG: model.debug(fn=‘logp’) doesn’t work with Potentials

[jonsedar]

Describe the issue:

model.debug() errors out when I have models that contain a Potential:

ValueError: Length of {name_of_potential} cannot be determined

There seems to be something going on in https://github.com/pymc-devs/pytensor/blob/7bb18f3a3590d47132245b7868b3a4a6587a4667/pytensor/tensor/__init__.py#L59 which fails for Potentials. Possibly because this one has shape None ?

_.type
$> TensorType(float64, shape=(None,))

See more discussion here: https://discourse.pymc.io/t/possible-bug-model-debug-fn-logp-doesnt-work-with-potentials/13150/3

Reproduceable code example:

import matplotlib.pyplot as plt
import numpy as np
import pymc as pm

rng = np.random.default_rng(42)
n = 100
y_obs = rng.normal(size=n)

with pm.Model() as mdl:
    y = pm.MutableData('y', y_obs)
    
    mu = pm.Normal('mu', mu=0.0, sigma=1.0)
    sigma = pm.InverseGamma('sigma', alpha=5.0, beta=4.0)
    norm_d = pm.Normal.dist(mu=mu, sigma=sigma, size=n)
    _ = pm.Potential('pot_yhat', pm.logp(norm_d, y))

print('Random:\n')
mdl.debug(fn='random', verbose=True)

print('\n\nlogP:\n')
mdl.debug(fn='logp', verbose=True)

Error message:

ValueError: Length of pot_yhat cannot be determined

PyMC version information:

Python implementation: CPython
Python version       : 3.10.12
IPython version      : 8.16.1

pymc    : 5.9.0
pytensor: 2.17.3

Compiler    : Clang 15.0.7 
OS          : Darwin
Release     : 22.6.0
Machine     : x86_64
Processor   : i386
CPU cores   : 8
Architecture: 64bit

Context for the issue:

This could be reclassified as a 1) a feature request to allow model.debug() to work on models with Potentials, and 2) a bug to be most easily fixed by a try/catch and a user warning