patch 9.1.0645: regex: wrong match when searching multi-byte char case-insensitive Commit: https://github.com/vim/vim/commit/22e8e12d9f5034e1984db0c567b281fda4de8dd7 Author: Christian Brabandt <cb@256bit.org> Date: Tue Jul 30 20:39:18 2024 +0200 patch 9.1.0645: regex: wrong match when searching multi-byte char case-insensitive Problem: regex: wrong match when searching multi-byte char case-insensitive (diffsetter) Solution: Apply proper case-folding for characters and search-string This patch does the following 4 things: 1) When the regexp engine compares two utf-8 codepoints case insensitive 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' 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 There is one tricky thing for the backtracing engine. We also need to calculate correctly the number of bytes to compare the 2 different utf-8 strings s1 and s2. So we will count the number of characters in s1 that the byte len specified. Then we count the number of bytes to step over the same number of characters in string s2 and then we can correctly compare the 2 utf-8 strings. 2) A similar 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. 3) 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. 4) When comparing characters using collections, we must also apply case folding to each character in the collection and not just to the current character from the search string. This doesn't apply to the NFA engine, because internally it converts collections to branches [abc] -> a\|b\|c fixes: #14294 closes: #14756 Signed-off-by: Christian Brabandt <cb@256bit.org>