[PATCH v2] tag: support --sort=<spec>

["Nguyễn Thái Ngọc Duy" <pclouds@gmail.com>]

--sort=refname:version (or --sort=refname:v for short) sorts tags as
if they are versions. --sort=-refname reverses the order (with or
without ":version"). This syntax is chosen to make it compatible with
future extension in "for-each-ref --sort"

GNU extension strverscmp is used so this is Linux only. Mac and
Windows will need to bundle a compat implementation (and long term we
may want to use compat version only so we can make XXX-rc, XXX-pre...
appear before XXX)

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
 The new prereq GNULINUX is an ugly workaround until people provide
 strverscmp compat implementation. I hope that will happen soon as
 strverscmp.c does not look very complex.

 Documentation/git-tag.txt |  6 +++++
 builtin/tag.c             | 69 +++++++++++++++++++++++++++++++++++++++++++----
 git-compat-util.h         |  7 +++++
 t/t7004-tag.sh            | 43 +++++++++++++++++++++++++++++
 t/test-lib.sh             |  2 ++
 5 files changed, 122 insertions(+), 5 deletions(-)

diff --git a/Documentation/git-tag.txt b/Documentation/git-tag.txt
index 404257d..d8633bb 100644
--- a/Documentation/git-tag.txt
+++ b/Documentation/git-tag.txt
@@ -95,6 +95,12 @@ OPTIONS
 	using fnmatch(3)).  Multiple patterns may be given; if any of
 	them matches, the tag is shown.
 
+--sort=<type>::
+	Sort in a specific order. Supported type is "refname"
+	(lexical order), "refname:version" or "refname:v" (tag names
+	are treated as version strings). Prepend "-" to reverse sorting
+	order.
+
 --column[=<options>]::
 --no-column::
 	Display tag listing in columns. See configuration variable
diff --git a/builtin/tag.c b/builtin/tag.c
index 74d3780..483d293 100644
--- a/builtin/tag.c
+++ b/builtin/tag.c
@@ -27,9 +27,16 @@ static const char * const git_tag_usage[] = {
 	NULL
 };
 
+#define STRCMP_SORT     0	/* must be zero */
+#define STRVERSCMP_SORT 1
+#define SORT_MASK       0x7fff
+#define REVERSE_SORT    0x8000
+
 struct tag_filter {
 	const char **patterns;
 	int lines;
+	int sort;
+	struct string_list tags;
 	struct commit_list *with_commit;
 };
 
@@ -166,7 +173,10 @@ static int show_reference(const char *refname, const unsigned char *sha1,
 			return 0;
 
 		if (!filter->lines) {
-			printf("%s\n", refname);
+			if (filter->sort)
+				string_list_append(&filter->tags, refname);
+			else
+				printf("%s\n", refname);
 			return 0;
 		}
 		printf("%-15s ", refname);
@@ -177,17 +187,39 @@ static int show_reference(const char *refname, const unsigned char *sha1,
 	return 0;
 }
 
+static int sort_by_version(const void *a_, const void *b_)
+{
+	const struct string_list_item *a = a_;
+	const struct string_list_item *b = b_;
+	return strverscmp(a->string, b->string);
+}
+
 static int list_tags(const char **patterns, int lines,
-			struct commit_list *with_commit)
+		     struct commit_list *with_commit, int sort)
 {
 	struct tag_filter filter;
 
 	filter.patterns = patterns;
 	filter.lines = lines;
+	filter.sort = sort;
 	filter.with_commit = with_commit;
+	memset(&filter.tags, 0, sizeof(filter.tags));
+	filter.tags.strdup_strings = 1;
 
 	for_each_tag_ref(show_reference, (void *) &filter);
-
+	if (sort) {
+		int i;
+		if ((sort & SORT_MASK) == STRVERSCMP_SORT)
+			qsort(filter.tags.items, filter.tags.nr,
+			      sizeof(struct string_list_item), sort_by_version);
+		if (sort & REVERSE_SORT)
+			for (i = filter.tags.nr - 1; i >= 0; i--)
+				printf("%s\n", filter.tags.items[i].string);
+		else
+			for (i = 0; i < filter.tags.nr; i++)
+				printf("%s\n", filter.tags.items[i].string);
+		string_list_clear(&filter.tags, 0);
+	}
 	return 0;
 }
 
@@ -427,6 +459,27 @@ static int parse_opt_points_at(const struct option *opt __attribute__((unused)),
 	return 0;
 }
 
+static int parse_opt_sort(const struct option *opt, const char *arg, int unset)
+{
+	int *sort = opt->value;
+	if (*arg == '-') {
+		*sort = REVERSE_SORT;
+		arg++;
+	} else
+		*sort = STRCMP_SORT;
+	if (!starts_with(arg, "refname") ||
+	    (arg[7] != ':' && arg[7] != '\0'))
+		die(_("unsupported sort field %s"), arg);
+	if (arg[7] == ':') {
+		const char *modifier = arg + 8;
+		if (!strcmp(modifier, "version") || !strcmp(modifier, "v"))
+			*sort |= STRVERSCMP_SORT;
+		else
+			die(_("unsupported modifier %s"), modifier);
+	}
+	return 0;
+}
+
 int cmd_tag(int argc, const char **argv, const char *prefix)
 {
 	struct strbuf buf = STRBUF_INIT;
@@ -437,7 +490,7 @@ int cmd_tag(int argc, const char **argv, const char *prefix)
 	struct create_tag_options opt;
 	char *cleanup_arg = NULL;
 	int annotate = 0, force = 0, lines = -1;
-	int cmdmode = 0;
+	int cmdmode = 0, sort = 0;
 	const char *msgfile = NULL, *keyid = NULL;
 	struct msg_arg msg = { 0, STRBUF_INIT };
 	struct commit_list *with_commit = NULL;
@@ -462,6 +515,10 @@ int cmd_tag(int argc, const char **argv, const char *prefix)
 					N_("use another key to sign the tag")),
 		OPT__FORCE(&force, N_("replace the tag if exists")),
 		OPT_COLUMN(0, "column", &colopts, N_("show tag list in columns")),
+		{
+			OPTION_CALLBACK, 0, "sort", &sort, N_("type"), N_("sort tags"),
+			PARSE_OPT_NONEG, parse_opt_sort
+		},
 
 		OPT_GROUP(N_("Tag listing options")),
 		{
@@ -509,7 +566,9 @@ int cmd_tag(int argc, const char **argv, const char *prefix)
 			copts.padding = 2;
 			run_column_filter(colopts, &copts);
 		}
-		ret = list_tags(argv, lines == -1 ? 0 : lines, with_commit);
+		if (lines != -1 && sort)
+			die(_("--sort and -n are incompatible"));
+		ret = list_tags(argv, lines == -1 ? 0 : lines, with_commit, sort);
 		if (column_active(colopts))
 			stop_column_filter();
 		return ret;
diff --git a/git-compat-util.h b/git-compat-util.h
index cbd86c3..22089e9 100644
--- a/git-compat-util.h
+++ b/git-compat-util.h
@@ -721,4 +721,11 @@ void warn_on_inaccessible(const char *path);
 /* Get the passwd entry for the UID of the current process. */
 struct passwd *xgetpwuid_self(void);
 
+#ifndef __GNU_LIBRARY__
+static inline int strverscmp(const char *s1, const char *s2)
+{
+	die("strverscmp() not supported");
+}
+#endif
+
 #endif
diff --git a/t/t7004-tag.sh b/t/t7004-tag.sh
index c8d6e9f..0b7b170 100755
--- a/t/t7004-tag.sh
+++ b/t/t7004-tag.sh
@@ -1380,4 +1380,47 @@ test_expect_success 'multiple --points-at are OR-ed together' '
 	test_cmp expect actual
 '
 
+test_expect_success GNULINUX 'lexical sort' '
+	git tag foo1.3 &&
+	git tag foo1.6 &&
+	git tag foo1.10 &&
+	git tag -l --sort=refname "foo*" >actual &&
+	cat >expect <<EOF &&
+foo1.10
+foo1.3
+foo1.6
+EOF
+	test_cmp expect actual
+'
+
+test_expect_success GNULINUX 'version sort' '
+	git tag -l --sort=refname:version "foo*" >actual &&
+	cat >expect <<EOF &&
+foo1.3
+foo1.6
+foo1.10
+EOF
+	test_cmp expect actual
+'
+
+test_expect_success GNULINUX 'reverse version sort' '
+	git tag -l --sort=-refname:version "foo*" >actual &&
+	cat >expect <<EOF &&
+foo1.10
+foo1.6
+foo1.3
+EOF
+	test_cmp expect actual
+'
+
+test_expect_success GNULINUX 'reverse lexical sort' '
+	git tag -l --sort=-refname "foo*" >actual &&
+	cat >expect <<EOF &&
+foo1.6
+foo1.3
+foo1.10
+EOF
+	test_cmp expect actual
+'
+
 test_done
diff --git a/t/test-lib.sh b/t/test-lib.sh
index 1531c24..5e8c39a 100644
--- a/t/test-lib.sh
+++ b/t/test-lib.sh
@@ -771,6 +771,8 @@ case $(uname -s) in
 	;;
 esac
 
+[ "$(uname -o)" = "GNU/Linux" ] && test_set_prereq GNULINUX
+
 ( COLUMNS=1 && test $COLUMNS = 1 ) && test_set_prereq COLUMNS_CAN_BE_1
 test -z "$NO_PERL" && test_set_prereq PERL
 test -z "$NO_PYTHON" && test_set_prereq PYTHON
-- 
1.9.0.40.gaa8c3ea