[Don-Yin]

B909 currently visits only the body of an if, so mutations in its condition or elif/else branches go unnoticed. For example:

items = [1, 2, 3]
for item in items:
    if item == 1:
        pass
    else:
        items.remove(item)

flake8 --isolated --select=B909 example.py reports nothing on main; with this change it reports the mutation on line 6.

This adds the missing visits and keeps alternate branches in separate mutation blocks, preserving the existing handling of unconditional break. The existing B909 fixture now covers elif, else, a mutating condition, and unconditional/conditional break controls.

Validation:

• RED on main: the updated fixture is missing four expected diagnostics; GREEN with the fix.
• Tox suites for Python 3.10–3.14 and pep8_naming pass. Python 3.15 was not available locally.
• pre-commit run --all-files passes (isort, Black, flake8, rstcheck).
• py313-mypy reports the same seven errors on pristine base bc1ec773c4bcaf121ca810cb78f5fcb3249d88c9 and this branch.

Measured B909 counts for six small snippets, including unchanged controls (inputs and diagnostic output):

[Copilot]

🟢 Approval recommended

The focused traversal fix has targeted regression coverage and no unresolved review findings.

No open issues 🎉

What changed in this PR

This PR fixes missed B909 diagnostics by extending the mutation checker to visit if conditions and alternate branches.

Changes:

• Visit conditions and elif/else branches while keeping alternate mutation blocks separate.
• Add regression cases for these paths and unconditional versus conditional break behavior.

File	Description
tests/​eval_files/​b909.py	Adds regression coverage for conditions, alternate branches, and break handling.
bugbear.py	Extends B909’s if traversal while preserving separate mutation blocks.

_{Review effort: Balanced}

[cooperlees]

Many thanks for this! Good enchancement

@copilot Can you add a CHANGE LOG entry for this?

[cooperlees]

@copilot Can you add a change log entry for this on to the PR in a new commit please.