Fix reverse slicing edge case

[rafaelha]

In three places across the kirin code base a slice object would be converted into start,stop,step triples using slice.indices, and then converted back into a slice.

There is a subtle issue with this illustrated by the following snippet:

nums = [0, 1, 2, 3, 4]
sl = slice(None, None, -1)
start, stop, step = sl.indices(len(nums))

print(nums[sl]) # [4, 3, 2, 1, 0]
print(nums[start:stop:step]) # []

Specifically, the following is an example of a incorrect rewrite that happened as a consequence

    @basic_no_opt
    def func():
        ylist = (0, 1, 2, 3, 4)
        return ylist[::-1]

    before = func()
    constprop = const.Propagate(func.dialects)
    frame, _ = constprop.run(func)
    Fixpoint(Walk(WrapConst(frame))).rewrite(func.code)
    inline_getitem = InlineGetItem()
    Fixpoint(Walk(Chain([inline_getitem, DeadCodeElimination()]))).rewrite(func.code)

    after = func()

    assert before == after
    # Failes because (4, 3, 2, 1, 0) != (,)

This PR removes all usage of slice.indices and introduces some new unit tests.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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[github-actions]

☂️ Python Coverage

current status: ✅

Overall Coverage

Lines	Covered	Coverage	Threshold	Status
11463	10208	89%	0%	🟢

New Files

No new covered files...

Modified Files

File	Coverage	Status
src/kirin/dialects/ilist/rewrite/inline_getitem.py	95%	🟢
src/kirin/dialects/py/indexing.py	90%	🟢
src/kirin/rewrite/getitem.py	96%	🟢
TOTAL	94%	🟢

updated for commit: f61f805 by action🐍

[github-actions]

PR Preview Action v1.6.2
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2025-11-03 14:22 UTC

[rafaelha]

This file is almost the same as getitem.py (list vs ilist)

Can code duplication be avoided?

[weinbe58]

LGTM