patch 9.1.0296: regexp: engines do not handle case-folding well Commit: https://github.com/vim/vim/commit/7a27c108e0509f3255ebdcb6558e896c223e4d23 Author: Christian Brabandt <cb@256bit.org> Date: Tue Apr 9 22:53:19 2024 +0200 patch 9.1.0296: regexp: engines do not handle case-folding well Problem: Regex engines do not handle case-folding well Solution: Correctly calculate byte length of characters to skip When the regexp engine compares two utf-8 codepoints case insensitively it may match an adjacent character, because it assumes it can step over as many bytes as the pattern contains. This however is not necessarily true because of case-folding, a multi-byte UTF-8 character can be considered equal to some single-byte value. Let's consider the pattern '?' and the string 's'. When comparing and ignoring case, the single character 's' matches, and since it matches Vim will try to step over the match (by the amount of bytes of the pattern), assuming that since it matches, the length of both strings is the same. However in that case, it should only step over the single byte value 's' so by 1 byte and try to start matching after it again. So for the backtracking engine we need to ensure: - we try to match the correct length for the pattern and the text - in case of a match, we step over it correctly The same thing can happen for the NFA engine, when skipping to the next character to test for a match. We are skipping over the regstart pointer, however we do not consider the case that because of case-folding we may need to adjust the number of bytes to skip over. So this needs to be adjusted in find_match_text() as well. A related issue turned out, when prog->match_text is actually empty. In that case we should try to find the next match and skip this condition. fixes: #14294 closes: #14433 Signed-off-by: Christian Brabandt <cb@256bit.org>