regexp/syntax: extract maxRepeat constant and document nested repetition limit by kunwar-vikrant · Pull Request #78232 · golang/go

kunwar-vikrant · 2026-03-19T18:15:41Z

The repeat count limit of 1000 was hardcoded as a magic number in
multiple places. Extract it into a named constant maxRepeat for clarity.

Additionally, the documentation stated that repeat counts above 1000
are rejected, but did not mention that nested repetitions have their
counts multiplied. For example, (?:[a-z]{4}){0,251} is rejected
because the product 4*251=1004 exceeds 1000, even though neither
individual count does. Document this behavior.

Add test cases for the exact boundary: {4}{250} (product 1000, valid)
and {4}{251} (product 1004, invalid).

Fixes #78222

google-cla · 2026-03-19T18:15:52Z

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gopherbot · 2026-03-19T18:30:03Z

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gopherbot · 2026-03-19T18:41:35Z

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gopherbot · 2026-04-02T23:39:23Z

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gopherbot · 2026-04-03T02:39:16Z

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gopherbot · 2026-04-04T07:09:01Z

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gopherbot · 2026-04-04T07:17:58Z

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gopherbot · 2026-04-04T07:26:51Z

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gopherbot · 2026-04-04T12:16:54Z

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gopherbot · 2026-04-04T12:35:11Z

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gopherbot · 2026-04-05T12:37:07Z

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Extract the magic number 1000 used as the maximum repetition count into a named constant maxRepeat in parse.go. This improves code clarity and makes the limit easier to find and reason about. The constant is used both in the repeat() method (via repeatIsValid) and in the parse() function's bounds check for {n,m} forms. Document the nested repetition product limit in doc.go: for nested repetitions, the product of the repetition counts must not exceed 1000. This is a Go-specific implementation restriction enforced by repeatIsValid in parse.go, extending the base restriction documented in the RE2 distribution's syntax.txt: https://github.com/google/re2/blob/main/doc/syntax.txt#L40 doc.go is generated by mksyntaxgo from the RE2 distribution: https://github.com/google/re2/blob/main/doc/mksyntaxgo The nested repetition product limit is Go-specific behavior not present in RE2's syntax.txt, similar to the Go-specific Unicode character class notes already added directly to doc.go. Fixes golang#78222

gopherbot · 2026-04-05T17:48:01Z

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gopherbot · 2026-04-05T17:57:06Z

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kunwar-vikrant force-pushed the fix/regexp-maxrepeat-constant branch from 35415d9 to fde35b5 Compare April 4, 2026 12:09

kunwar-vikrant force-pushed the fix/regexp-maxrepeat-constant branch from fde35b5 to a4b25cd Compare April 5, 2026 17:42

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