@matheusbsbs / matheus-bagliano / commits / 0324e8fc6b

word diff: handle zero length matches

If find_word_boundaries() encounters a zero length match (which can be caused by matching a newline or using '*' instead of '+' in the regex) we stop splitting the input into words which generates an inaccurate diff. To fix this increment the start point when there is a zero length match and try a new match. This is safe as posix regular expressions always return the longest available match so a zero length match means there are no longer matches available from the current position. Commit bf82940dbf1 (color-words: enable REG_NEWLINE to help user, 2009-01-17) prevented matching newlines in negated character classes but it is still possible for the user to have an explicit newline match in the regex which could cause a zero length match. One could argue that having explicit newline matches or using '*' rather than '+' are user errors but it seems to be better to work round them than produce inaccurate diffs. Signed-off-by: Phillip Wood <phillip.wood@dunelm.org.uk> Signed-off-by: Junio C Hamano <gitster@pobox.com>

Phillip Wood committed May 4, 2021 at 09:27 UTC 0324e8fc6b297c9e61745dc4e7d110780334157d

2 files changed +12 -3

diff.c

+7 -3

@@ -2053,7 +2053,7 @@ static void fn_out_diff_words_aux(void *priv,

2053 static int find_word_boundaries(mmfile_t *buffer, regex_t *word_regex,

2054 int *begin, int *end)

2055 {

2056 - if (word_regex && *begin < buffer->size) {

2056 + while (word_regex && *begin < buffer->size) {

2057 regmatch_t match[1];

2058 if (!regexec_buf(word_regex, buffer->ptr + *begin,

2059 buffer->size - *begin, 1, match, 0)) {

@@ -2061,9 +2061,13 @@ static int find_word_boundaries(mmfile_t *buffer, regex_t *word_regex,

2061 '\n', match[0].rm_eo - match[0].rm_so);

2062 *end = p ? p - buffer->ptr : match[0].rm_eo + *begin;

2063 *begin += match[0].rm_so;

2064 - return *begin >= *end;

2064 + if (*begin == *end)

2065 + (*begin)++;

2066 + else

2067 + return *begin > *end;

2068 + } else {

2069 + return -1;

2070 }

2066 - return -1;

2071 }

2072

2073 /* find the next word */

t/t4034-diff-words.sh

@@ -184,6 +184,11 @@ test_expect_success 'word diff with a regular expression' '

184 word_diff --color-words="[a-z]+"

185 '

186

187 +test_expect_success 'word diff with zero length matches' '

188 + cp expect.letter-runs-are-words expect &&

189 + word_diff --color-words="[a-z${LF}]*"

190 +'

191 +

192 test_expect_success 'set up a diff driver' '

193 git config diff.testdriver.wordRegex "[^[:space:]]" &&

194 cat <<-\EOF >.gitattributes