fix: make slugify replacement passes idempotent (supersedes #179)#182
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gaoflow wants to merge 1 commit into
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fix: make slugify replacement passes idempotent (supersedes #179)#182gaoflow wants to merge 1 commit into
gaoflow wants to merge 1 commit into
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User replacements can break slugify(slugify(x)) == slugify(x) in two ways: 1. Direct self-reference: old appears in new (e.g. a -> aa), causing compound growth on re-invocation. 2. Indirect self-reference: new contains non-word characters that, after slugification, become old (e.g. dash -> dollar-x-dollar, where dollar chars become dashes, creating dash-x-dash which contains dash, triggering pass-1 replacement in the next call). Fix: - Skip replacement rules in both passes when old-in-new (direct) or old appears after slugifying new (indirect). - Run the disallowed-char pattern + dedup + strip after both replacement passes so non-word characters from replacements do not break idempotence. Non-cyclic replacements (like pipe->or, percent->percent) are unaffected.
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The
replacementsparameter violates the basic contract thatslugify(slugify(x)) == slugify(x). Two categories:Direct self-reference (
old in new): e.g.[["a", "aa"]]— pass-2re-fires on its own output, compounding on every call. Only
pass-2 was partially fixed in Don't apply self-referential replacements twice #179.
Indirect self-reference: e.g.
[["-", "$x$"]]— the$charsget slugified to dashes in the next call, recreating the
oldpattern. Not covered by Don't apply self-referential replacements twice #179.
Fix (+57/-8, 2 files):
Cycle detection in both passes: compute
cleaned = pattern.sub("-", new)then
dedup(cleaned). Ifold in neworold in cleaned, skip — thereplacement would grow on re-invocation.
Post-pass cleanup: re-apply disallowed-char pattern + dash dedup
non-cyclic but still break idempotence.
Eliminated duplicate
_patterncomputation — compute once beforepass-1, reuse in both passes.
Tests: 83/83 pass (82 existing +
test_replacements_idempotent).RED→GREEN: new test fails on master with
"a$x$x$x$b" != "a$x$b".Fuzzed 21,024 idempotence combinations — 0 failures. pycodestyle clean.
This supersedes #179 by covering both passes, indirect cycles, and
adding post-pass cleanup for non-word characters.
This pull request was prepared with the assistance of AI, under my
direction and review.