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Compile capturing regexes with the backtracking matcher

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irregex builds a POSIX leftmost-longest DFA for a pattern when it can, and jolt
used it for everything. For a pattern with an alternation whose branches have
capturing groups, that DFA leaks a non-participating branch's group: e.g.
#"(?:([0-9])|([0-9])r([0-9]+))" on "2r11" left group 1 = "2" instead of nil, so
tools.reader (rewrite-clj's dep) misread 2r1100 as 2 and 16rFF as 16.

java.util.regex is itself a leftmost-first backtracking engine, so compile a
capturing pattern with irregex's backtracking matcher ('backtrack): its submatch
semantics match the JVM and it clears a losing branch's group. Non-capturing
patterns keep the DFA — with no groups to read, its whole-match result is all a
caller sees, and it avoids backtracking's worst case. The submatch count comes
from a first cheap compile; a capturing pattern recompiles once and caches.

This clears the last rewrite-clj parser-test failure (now 772/0/0). Corpus rows
for the alternation-group case and the radix read. make test green.
This commit is contained in:
Yogthos 2026-07-01 12:48:12 -04:00
parent e2d842b073
commit 7c4f9bb974
2 changed files with 17 additions and 2 deletions
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test/chez/corpus.edn
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@ -1,5 +1,7 @@
[
{:suite "host-interop / reify ILookup" :label "(get reify k) / (:k reify) / (get reify k d) route to valAt" :expected "[1 1 :dflt]" :actual "(let [r (reify clojure.lang.ILookup (valAt [_ k] (get {:a 1} k)) (valAt [_ k d] (get {:a 1} k d)))] [(:a r) (get r :a) (get r :z :dflt)])"}
{:suite "regex / alternation submatch" :label "a non-participating alternation group is nil, not a stale capture" :expected "[\"2r11\" nil \"2\" \"11\"]" :actual "(re-matches #\"(?:([0-9])|([0-9])r([0-9]+))\" \"2r11\")"}
{:suite "regex / radix read" :label "tools.reader-style radix parse: winning branch's groups, not the losing one's" :expected "[12 255]" :actual "[(read-string \"2r1100\") (read-string \"16rFF\")]"}
{:suite "numbers / comparison error class" :label "nil operand is NPE, non-number is CCE" :expected "[\"java.lang.NullPointerException\" \"java.lang.ClassCastException\"]" :actual "[(try (> nil 5) (catch Throwable e (.getName (class e)))) (try (> :k 5) (catch Throwable e (.getName (class e))))]"}
{:suite "reader / quoted #inst constructs a value" :label "a quoted #inst literal is the constructed Date, not a tagged form" :expected "\"(f #inst \\\"1939-01-01T00:00:00.000-00:00\\\")\"" :actual "(pr-str (quote (f #inst \"1939\")))"}
{:suite "fn / kwargs trailing map" :label "(f :k v {map}) and (f {map}) both bind & {:as m}" :expected "[{:x 1 :y 2} {:x 1 :y 2}]" :actual "[((fn [a & {:as m}] m) 1 :x 1 {:y 2}) ((fn [a & {:as m}] m) 1 {:x 1 :y 2})]"}