fix: WPS457 false positive when while True is inside try/except

[stakeswky]

Fixes #3603

Problem

WPS457 (InfiniteWhileLoopViolation) was incorrectly triggered when a while True loop was wrapped in a try/except block:

def factory() -> Iterator[bytes]:
    try:
        while True:
            yield async_to_sync(async_anext)(iterator)
    except StopAsyncIteration:
        pass

This is not an infinite loop — the except handler provides a clear termination path. The previous implementation only checked for break/raise/return/ExceptHandler inside the while body, but missed the case where the enclosing try/except itself acts as the exit mechanism.

Fix

Added is_in_try_except() helper in wemake_python_styleguide/logic/tree/loops.py that walks up the AST parent chain to detect if the while node is directly inside a try block that has at least one except handler.

In _check_infinite_while_loop, if is_in_try_except() returns True, the violation is suppressed.

Note: A try/finally without except still triggers WPS457, since finally does not catch exceptions and cannot terminate the loop.

Tests

Added three new correct cases (correct_while8/9/10) covering the reported pattern, and one new wrong case (wrong_while3) for try/finally without except.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (bf05af9) to head (b2813ca).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##            master     #3604   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          368       368           
  Lines        12291     12302   +11     
  Branches       853       854    +1     
=========================================
+ Hits         12291     12302   +11     

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[sobolevn]

Thanks! If you are using AI, please, double check the produced results :)

[sobolevn]

Please, move correct examples to correct examples' section.

[stakeswky]

Done — moved correct examples up to the correct section.

[sobolevn]

All these examples are the same from the AST's point of view.

Please, remove duplicates.

[stakeswky]

Good point. Removed the duplicates — kept one simple case (correct_while9) and replaced the other with a nested variant (correct_while10) so they're structurally distinct.

[sobolevn]

Why not using get_closest_parent()?

[stakeswky]

Refactored to use get_closest_parent() — much cleaner. Thanks for the pointer.

[sobolevn]

Please, add more nesting in the tests. But, keep them minimal.

[stakeswky]

Added correct_while10 with nested try/except inside the while loop to cover deeper nesting, kept it minimal.

[stakeswky]

Thanks for the detailed review! I've addressed all four points:

1. get_closest_parent(): Refactored is_in_try_except() to use walk.get_closest_parent(node, (*_SCOPE_BOUNDARIES, ast.Try)) — finds the nearest Try or scope-boundary parent in one call, then checks if it's a Try with handlers.

2. Correct examples section: Moved correct_while8/9/10 above the # Do raise: section where they belong.

3. Removed duplicate: correct_while9 (same AST as correct_while8 — both are def fn(): try: while True: yield; except: pass) has been removed and replaced with a simpler top-level try/except case.

4. More nesting: Added correct_while10 with a nested try/except inside the while True body, inside an outer try/except.

[sobolevn]

Suggested change

	try:
	while True:
	yield some()
	except StopIteration:
	pass
	try:
	if some:
	while True:
	yield some
	except StopIteration:
	pass

[stakeswky]

Applied your suggestion — replaced with try: if some: while True: yield some; except StopIteration: pass to test deeper nesting.

[sobolevn]

You don't need a variable for a single use of values.

[stakeswky]

Done — removed _SCOPE_BOUNDARIES and inlined the tuple directly in the get_closest_parent() call.

[sobolevn]

you never test try being further in hierarchy then scope boundaries.

[stakeswky]

Added wrong_while4: a while True inside a function that is itself inside a try/except — the scope boundary (function def) should block the try from exempting the loop, so it raises InfiniteWhileLoopViolation. Included in test_wrong_while_loops_with_try.

[sobolevn]

This comment is not required.

[stakeswky]

Removed.