PLR5501 and PLW0120 safe fixes delete a trailing comment on the else: line #29395

Summary

The safe fixes for collapsible-else-if (PLR5501) and useless-else-on-loop (PLW0120) delete a comment that
trails the else: they remove. The superfluous-else-* fixes (RET505–RET508) keep such a comment and move it to
its own line.

def f(a, b):
    if a:
        return 1
    else:  # explain the fallback
        if b:
            return 2
        else:
            return 3

ruff check --isolated --select PLR5501 --fix repro.py:

def f(a, b):
    if a:
        return 1
    elif b:
        return 2
    else:
        return 3

def f(xs):
    for x in xs:
        if x:
            return x
    else:  # nothing found
        return None

ruff check --isolated --select PLW0120 --fix repro.py:

def f(xs):
    for x in xs:
        if x:
            return x
    return None

For comparison, ruff check --isolated --select RET505 --fix on

def f(a):
    if a:
        return 1
    else:  # the fallback
        return 2

keeps the comment:

def f(a):
    if a:
        return 1
    # the fallback
    return 2

remove_else in flake8_return/rules/function.rs handles this explicitly ("if there is a comment on the same line as
the Colon, let's keep it"). convert_to_elif (PLR5501) and remove_else in useless_else_on_loop.rs (PLW0120)
replace from the start of the else line and keep only what follows that line. #9779 and #13545 fixed own-line comments
between else: and the nested if; those are kept now, but a comment on the else: line itself is not.

Real-world cases: pydantic 2.14.1, pydantic/deprecated/json.py lines 109 and 132
(else: # We have exited the for loop without finding a suitable encoder), and contourpy 1.4.0,
tests/util_config.py line 445 (else: # !quad_as_tri).

(Found while running Ruff's safe fixes over the top PyPI packages.)

Version

ruff 0.17.0