feat!: CoW X by default when setting i.e., subset.X = ... does not update parent of subset

[ilan-gold]

• Next step in feat!: Unify X and layers #1707 (comment)
• Tests added
• Release note added (or unnecessary)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.78%. Comparing base (6a25200) to head (653998f).
⚠️ Report is 54 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2338      +/-   ##
==========================================
- Coverage   86.95%   86.78%   -0.17%     
==========================================
  Files          46       46              
  Lines        7390     7364      -26     
==========================================
- Hits         6426     6391      -35     
- Misses        964      973       +9     

Files with missing lines	Coverage Δ
src/anndata/_core/anndata.py	81.98% <100.00%> (-1.71%)	⬇️

[ilan-gold]

@Intron7 Can you run this branch in your tests perhaps? I could see you explicitly or implicitly relying on some sort of behavior here that we are not accounting for.

[flying-sheep]

Important

Can we get rid of ArrayView in this PR?

[flying-sheep]

check here that the view has the changed values?

[ilan-gold]

But it's checked below? The oprevious lines I changed i.e., assert adata[:, 0].X.tolist() == np.reshape([1, 4, 7], (3, 1)).tolist() are specifically checking that the parent didn't change despite the update

[flying-sheep]

I mean that adata[:2, 0].X = [0, 0] creates a view, then actualizes it and sets the new non-view AnnData’s values. But I guess that’s tested elsewhere already.

maybe at least check that that line specifically raises the “view as actual” warning

[ilan-gold]

Can we get rid of ArrayView in this PR?

No, I should clarify that this is only making CoW subset.X = ... which previously would have updated the actual anndata. This is distinct from X = subset.X and then X[another_subset] = ... which is CoW. I will update hte PR title. My zulip freakout was about "do we need views at all", which has to do with the later point.