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`<regex>`: Fix word bounds `\b` and `\B` when applied to the empty string by muellerj2 · Pull Request #5375 · microsoft/STL · GitHub
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<regex>: Fix word bounds \b and \B when applied to the empty string #5375

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Merged
merged 3 commits into from
Apr 10, 2025
Merged

<regex>: Fix word bounds \b and \B when applied to the empty string #5375

merged 3 commits into from
Apr 10, 2025

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@muellerj2
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Fixes #5371.

The ECMAScript standard effectively states that \b matches a position i in the string iff IsWordChar(i-1) xor IsWordChar(i) is true. It also defines that for positions i = -1 and i = length(input), IsWordChar(i) always returns false. Thus, \b does not match anything in the empty string.

Since \b does not match the empty string, the flags match_not_bow and match_not_eow don't matter in this case.

@muellerj2 muellerj2 requested a review from a team as a code owner March 28, 2025 17:31
@github-project-automation github-project-automation bot moved this to Initial Review in STL Code Reviews Mar 28, 2025
@StephanTLavavej StephanTLavavej added bug Something isn't working regex meow is a substring of homeowner labels Mar 29, 2025
@StephanTLavavej StephanTLavavej self-assigned this Mar 29, 2025
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StephanTLavavej reviewed Apr 1, 2025
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Thanks for the fix, test coverage, and clear writeup with citations! I pushed a trivial change to use raw string literals.

@StephanTLavavej StephanTLavavej moved this from Initial Review to Ready To Merge in STL Code Reviews Apr 1, 2025
@StephanTLavavej StephanTLavavej removed their assignment Apr 1, 2025
@StephanTLavavej StephanTLavavej mentioned this pull request Apr 1, 2025
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@StephanTLavavej StephanTLavavej moved this from Ready To Merge to Merging in STL Code Reviews Apr 9, 2025
@StephanTLavavej StephanTLavavej self-assigned this Apr 9, 2025
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I'm mirroring this to the MSVC-internal repo - please notify me if any further changes are pushed.

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Resolved adjacent-add conflict in VSO_0000000_regex_use.

@StephanTLavavej StephanTLavavej merged commit b69d5f5 into microsoft:main Apr 10, 2025
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@github-project-automation github-project-automation bot moved this from Merging to Done in STL Code Reviews Apr 10, 2025
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🐝 🪲 🐞

@muellerj2 muellerj2 deleted the regex-fix-word-bounds-on-empty-string branch April 13, 2025 13:49
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@StephanTLavavej StephanTLavavej StephanTLavavej approved these changes

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bug Something isn't working regex meow is a substring of homeowner

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<regex>: \b and \B are backwards on empty strings

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