meta.find_undeclared_variables returning variables set in if blocks as of 3.1.5

[alext]

I've observed a change in behaviour between 3.1.4 and 3.1.5 where meta.find_undeclared_variables is now returning variables that are set in all branches of an if statement.

For example with the following:

from jinja2 import Environment, meta

env = Environment()

template = """\
{% if control == 'something' %}
    {% set output = 1 %}
{% elif control == 'something else' %}
    {% set output = 2 %}
{% else %}
    {% set output = 3 %}
{% endif %}
{{ output }}
"""
result = meta.find_undeclared_variables(env.parse(template))
assert result == {'control'}

With jinja2 version 3.1.4, this runs without error. With jinja2 version 3.1.5, this errors becasue result contains both "control" and "output". I believe the 3.1.4 behaviour is correct in this instance.

Reading the changelog, I suspect that the fix for #1253 (PR #1665) looks likely to be the cause of this change.

Environment:

• Python version: 3.10.12
• Jinja version: 3.1.5

[alext]

I've just tested using jinja2 3.1.5 with the changes from #1665 reverted, and this results in the same behaviour as 3.1.4.

[davidism]

I'm happy to review a PR or suggested fix.