924060929 commented on PR #64064:
URL: https://github.com/apache/doris/pull/64064#issuecomment-4841547593
Nice optimization — the pattern-shape guards (escape handling, char-class
tracking, inline-flag detection) are careful. One correctness issue on the
`regexp_replace` → `regexp_replace_one` rewrite:
**A quantified leading anchor defeats the "single match" assumption.**
`startsWithUnescapedCaret()` only checks `charAt(0) == '^'`, not whether the
`^` is an *effective* anchor. When the leading `^` can match zero times (`^?`,
`^*`, `^{0,n}`), the anchor is optional and the pattern can match at multiple
positions, so `GlobalReplace` ≠ `Replace`. These patterns still pass every
current guard (`charAt(0) == '^'`, no `|`, no `(?m)`) and get rewritten.
Verified on a live instance (RE2 behavior, independent of this PR):
```sql
regexp_replace('aa','^?a','X') -- 'XX' -> regexp_replace_one: 'Xa'
(wrong)
regexp_replace('aaa','^*a','X') -- 'XXX' -> 'Xaa' (wrong)
regexp_replace('aa','^{0,2}a','X') -- 'XX' -> 'Xa' (wrong)
```
Suggestion: treat the leading `^` as an anchor only when it is **not**
immediately followed by a zero-allowing quantifier (`?`, `*`, `{0,…}`); `^+` /
`^{1,}` stay safe. The trailing-`$` side isn't affected (a quantifier would
push `$` off the last position), and the `regexp_extract` `.*$` trim doesn't
rely on anchoring (verified equivalent).
Param handling otherwise looks good: arity (3/4 for replace, fixed-3 for
extract) is safe, and the group-index `>= 1` check is correct — no upper bound
needed, since the BE returns empty for out-of-range groups identically
before/after the rewrite.
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