[typing] Add find_assigned_value helper func to typing.rs to retrieve value of a given variable id

[qdegraaf]

Summary

Adds find_assigned_value a function which gets the &Expr assigned to a given id if one exists in the semantic model.

Open TODOs:

• Handle binding.kind.is_unpacked_assignment(): I am bit confused by this one. The snippet from its documentation does not appear to be counted as an unpacked assignment and the only ones I could find for which that was true were invalid Python like:

x, y = 1 

• How to handle AugAssign. Can we combine statements like:

(a, b) = [(1, 2, 3), (4,)]
a += (6, 7)

to get the full value for a? Code currently just returns None for these assign types

• Multi target assigns

m_c = (m_d, m_e) = (0, 0)
trio.sleep(m_c)  # OK
trio.sleep(m_d)  # TRIO115
trio.sleep(m_e)  # TRIO115

Test Plan

Used the function in two rules:

• TRIO115
• PERF101

Expanded both their fixtures for explicit multi target check

[github-actions]

ruff-ecosystem results

Linter (stable)

✅ ecosystem check detected no linter changes.

Linter (preview)

✅ ecosystem check detected no linter changes.

[qdegraaf]

@charliermarsh I'm thinking the binding.kind.is_unpacked_assignment() can be left as a TODO for later when it is necessary? Let me know if that is acceptable. I think it would be good to review current set-up and logic first regardless, before expanding further.

[charliermarsh]

What happens here in the case of multi-target assignments?

[qdegraaf]

Good catch. It works for

x = y = 0

Added example of that to TRIO115 fixture

Does not work for

(x, y) = [a, b] = (0, 0)

Which will only manage to retrieve the values for x and y right now.

Would it be an idea to set up unit tests for this and the other new func in the module? If so, is there a leading example of non plugin unit tests I can have a look at?

[charliermarsh]

Is it able to detect y in x = y = 0?

[charliermarsh]

Yeah, we don't have great infrastructure for this. I'd probably just recommend adding more trio test cases as a means of testing this behavior.

[qdegraaf]

Is it able to detect y in x = y = 0?

Yeah this one works. But if one of the targets is a collection there are issues. e.g.

a = (x, y) = (0, 0)
(a, b) = [c, d] = [0, 0]

Not entirely sure how to best fix that. Flag it as a multi assign if the top-level targets has a length larger than 1 and add a separate branch for that? Or are there single target scenarios that could be mistaken then?

[charliermarsh]

I think there's one more case to consider:

m_c = (m_d, m_e) = (0, 0)
trio.sleep(m_c)  # OK
trio.sleep(m_d)  # TRIO115
trio.sleep(m_e)  # TRIO115

Right now, these all get matched to (0, 0).

[qdegraaf]

I think there's one more case to consider:

m_c = (m_d, m_e) = (0, 0)
trio.sleep(m_c)  # OK
trio.sleep(m_d)  # TRIO115
trio.sleep(m_e)  # TRIO115

Right now, these all get matched to (0, 0).

Ho missed this one when I posted #8583 (comment)

Added it to TODOs. Gonna look at this again, see if there's a way to be aware of the multi target nature of the assign before drilling down.