Improve collect_default_updates

[ricardoV94]

This is part of some work to make CustomDist more powerful, specially for timeseries distributions.

Immediate changes:

• It works with nested RNGs
• It raises error if RNG used in SymbolicRandomVariable is not given an update
• It raises warning if same RNG is used in multiple nodes

[codecov]

Codecov Report

Merging #6620 (87c4fe7) into main (46f8e2f) will decrease coverage by 0.50%.
The diff coverage is 100.00%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6620      +/-   ##
==========================================
- Coverage   91.94%   91.44%   -0.50%     
==========================================
  Files          94       94              
  Lines       15831    15845      +14     
==========================================
- Hits        14556    14490      -66     
- Misses       1275     1355      +80     

Impacted Files	Coverage Δ
pymc/distributions/distribution.py	96.30% <100.00%> (-0.31%)	⬇️
pymc/pytensorf.py	88.78% <100.00%> (-3.57%)	⬇️

... and 4 files with indirect coverage changes

[michaelosthege]

Extracting this iterator into a local variable would make it easier to read.

Extracting it into a function could make it easier to test too?

[ricardoV94]

Removed the TODO, by adding a direct test. I think this test makes the behavior of the function pretty clear, including the hard to read iterator?

https://github.com/pymc-devs/pymc/blob/d8c57f4af5e272a0d924c76caae625d6f1d0fd1f/tests/test_pytensorf.py#L542-L553

[michaelosthege]

I still find the iterator hard to read, but proceed on your discretion

[ricardoV94]

I am still being stubborn, but added a comment and renamed the iterator variable to be a bit more obvious. Will merge when tests pass again :)

pymc/pymc/pytensorf.py

Lines 1062 to 1073 in 87c4fe7

	# Iterate over input RNGs. Only consider shared RNGs if `must_be_shared==True`
	for input_rng in (
	inp
	for inp in graph_inputs(outputs, blockers=inputs)
	if (
	(not must_be_shared or isinstance(inp, SharedVariable))
	and isinstance(inp.type, RandomType)
	)
	):
	# Even if an explicit default update is provided, we call it to
	# issue any warnings about invalid random graphs.
	default_update = find_default_update(clients, input_rng)

Thanks!