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>

1 files changed, 31 insertions, 0 deletions

diff --git a/t/t7004-tag.sh b/t/t7004-tag.sh
index c7aaace8cd..e2efe312dc 100755
--- a/t/t7004-tag.sh
+++ b/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