versioncmp: use earliest-longest contained suffix to determine sorting order

When comparing tagnames, it is possible that a tagname contains more
than one of the configured prerelease suffixes around the first
different character.  After fixing a bug in the previous commit such a
tagname is sorted according to the contained suffix which comes first
in the configuration.  This is, however, not quite the right thing to
do in the following corner cases:

  1.   $ git -c versionsort.suffix=-bar
             -c versionsort.suffix=-foo-baz
             -c versionsort.suffix=-foo-bar
             tag -l --sort=version:refname 'v1*'
       v1.0-foo-bar
       v1.0-foo-baz

     The suffix of the tagname 'v1.0-foo-bar' is clearly '-foo-bar',
     so it should be listed last.  However, as it also contains '-bar'
     around the first different character, it is listed first instead,
     because that '-bar' suffix comes first the configuration.

  2. One of the configured suffixes starts with the other:

       $ git -c versionsort.prereleasesuffix=-pre \
             -c versionsort.prereleasesuffix=-prerelease \
             tag -l --sort=version:refname 'v2*'
       v2.0-prerelease1
       v2.0-pre1
       v2.0-pre2

     Here the tagname 'v2.0-prerelease1' should be the last.  When
     comparing 'v2.0-pre1' and 'v2.0-prerelease1' the first different
     characters are '1' and 'r', respectively.  Since this first
     different character must be part of the configured suffix, the
     '-pre' suffix is not recognized in the first tagname.  OTOH, the
     '-prerelease' suffix is properly recognized in
     'v2.0-prerelease1', thus it is listed first.

Improve version sort in these corner cases, and

  - look for a configured prerelease suffix containing the first
    different character or ending right before it, so the '-pre'
    suffixes are recognized in case (2).  This also means that
    when comparing tagnames 'v2.0-pre1' and 'v2.0-pre2',
    swap_prereleases() would find the '-pre' suffix in both, but then
    it will return "undecided" and the caller will do the right thing
    by sorting based in '1' and '2'.

  - If the tagname contains more than one suffix, then give precedence
    to the contained suffix that starts at the earliest offset in the
    tagname to address (1).

  - If there are more than one suffixes starting at that earliest
    position, then give precedence to the longest of those suffixes,
    thus ensuring that in (2) the tagname 'v2.0-prerelease1' won't be
    sorted based on the '-pre' suffix.

Add tests for these corner cases and adjust the documentation
accordingly.

Signed-off-by: SZEDER Gábor <szeder.dev@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/config.txt

@@ -3049,8 +3049,10 @@ order of suffixes in the config file determines the sorting order
 (e.g. if "-pre" appears before "-rc" in the config file then 1.0-preXX
 is sorted before 1.0-rcXX).
 If more than one suffixes match the same tagname, then that tagname will
-be sorted according to the matching suffix which comes first in the
-configuration.
+be sorted according to the suffix which starts at the earliest position in
+the tagname.  If more than one different matching suffixes start at
+that earliest position, then that tagname will be sorted according to the
+longest of those suffixes.
 The sorting order between different suffixes is undefined if they are
 in multiple config files.
 

t/t7004-tag.sh

@@ -1564,6 +1564,37 @@ test_expect_success 'version sort with prerelease reordering, multiple suffixes
 	test_cmp expect actual
 '
 
+test_expect_success 'version sort with prerelease reordering, multiple suffixes match the same tag' '
+	test_config versionsort.prereleaseSuffix -bar &&
+	git config --add versionsort.prereleaseSuffix -foo-baz &&
+	git config --add versionsort.prereleaseSuffix -foo-bar &&
+	git tag foo1.8-foo-bar &&
+	git tag foo1.8-foo-baz &&
+	git tag foo1.8 &&
+	git tag -l --sort=version:refname "foo1.8*" >actual &&
+	cat >expect <<-\EOF &&
+	foo1.8-foo-baz
+	foo1.8-foo-bar
+	foo1.8
+	EOF
+	test_cmp expect actual
+'
+
+test_expect_success 'version sort with prerelease reordering, multiple suffixes match starting at the same position' '
+	test_config versionsort.prereleaseSuffix -pre &&
+	git config --add versionsort.prereleaseSuffix -prerelease &&
+	git tag foo1.9-pre1 &&
+	git tag foo1.9-pre2 &&
+	git tag foo1.9-prerelease1 &&
+	git tag -l --sort=version:refname "foo1.9*" >actual &&
+	cat >expect <<-\EOF &&
+	foo1.9-pre1
+	foo1.9-pre2
+	foo1.9-prerelease1
+	EOF
+	test_cmp expect actual
+'
+
 test_expect_success 'version sort with very long prerelease suffix' '
 	test_config versionsort.prereleaseSuffix -very-looooooooooooooooooooooooong-prerelease-suffix &&
 	git tag -l --sort=version:refname

versioncmp.c

@@ -27,14 +27,18 @@ static int initialized;
 /*
  * off is the offset of the first different character in the two strings
  * s1 and s2. If either s1 or s2 contains a prerelease suffix containing
- * that offset, then that string will be forced to be on top.
+ * that offset or a suffix ends right before that offset, then that
+ * string will be forced to be on top.
  *
  * If both s1 and s2 contain a (different) suffix around that position,
  * their order is determined by the order of those two suffixes in the
  * configuration.
  * If any of the strings contains more than one different suffixes around
  * that position, then that string is sorted according to the contained
- * suffix which comes first in the configuration.
+ * suffix which starts at the earliest offset in that string.
+ * If more than one different contained suffixes start at that earliest
+ * offset, then that string is sorted according to the longest of those
+ * suffixes.
  *
  * Return non-zero if *diff contains the return value for versioncmp()
  */
@@ -44,27 +48,40 @@ static int swap_prereleases(const char *s1,
 			    int *diff)
 {
 	int i, i1 = -1, i2 = -1;
+	int start_at1 = off, start_at2 = off, match_len1 = -1, match_len2 = -1;
 
 	for (i = 0; i < prereleases->nr; i++) {
 		const char *suffix = prereleases->items[i].string;
-		int j, start, suffix_len = strlen(suffix);
+		int j, start, end, suffix_len = strlen(suffix);
 		if (suffix_len < off)
-			start = off - suffix_len + 1;
+			start = off - suffix_len;
 		else
 			start = 0;
-		for (j = start; j <= off; j++)
-			if (i1 == -1 && starts_with(s1 + j, suffix)) {
+		end = match_len1 < suffix_len ? start_at1 : start_at1-1;
+		for (j = start; j <= end; j++)
+			if (starts_with(s1 + j, suffix)) {
 				i1 = i;
+				start_at1 = j;
+				match_len1 = suffix_len;
 				break;
 			}
-		for (j = start; j <= off; j++)
-			if (i2 == -1 && starts_with(s2 + j, suffix)) {
+		end = match_len2 < suffix_len ? start_at2 : start_at2-1;
+		for (j = start; j <= end; j++)
+			if (starts_with(s2 + j, suffix)) {
 				i2 = i;
+				start_at2 = j;
+				match_len2 = suffix_len;
 				break;
 			}
 	}
 	if (i1 == -1 && i2 == -1)
 		return 0;
+	if (i1 == i2)
+		/* Found the same suffix in both, e.g. "-rc" in "v1.0-rcX"
+		 * and "v1.0-rcY": the caller should decide based on "X"
+		 * and "Y". */
+		return 0;
+
 	if (i1 >= 0 && i2 >= 0)
 		*diff = i1 - i2;
 	else if (i1 >= 0)