ref-filter: add support to sort by version

Add support to sort by version using the "v:refname" and
"version:refname" option. This is achieved by using the 'versioncmp()'
function as the comparing function for qsort.

This option is included to support sorting by versions in `git tag -l`
which will eventually be ported to use ref-filter APIs.

Add documentation and tests for the same.

Mentored-by: Christian Couder <christian.couder@gmail.com>
Mentored-by: Matthieu Moy <matthieu.moy@grenoble-inp.fr>
Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-for-each-ref.txt

@@ -157,6 +157,9 @@ For sorting purposes, fields with numeric values sort in numeric
 order (`objectsize`, `authordate`, `committerdate`, `taggerdate`).
 All other fields are used to sort in their byte-value order.
 
+There is also an option to sort by versions, this can be done by using
+the fieldname `version:refname` or its alias `v:refname`.
+
 In any case, a field name that refers to a field inapplicable to
 the object referred by the ref does not cause an error.  It
 returns an empty string instead.

ref-filter.c

@@ -11,6 +11,8 @@
 #include "ref-filter.h"
 #include "revision.h"
 #include "utf8.h"
+#include "git-compat-util.h"
+#include "version.h"
 
 typedef enum { FIELD_STR, FIELD_ULONG, FIELD_TIME } cmp_type;
 
@@ -1439,19 +1441,19 @@ static int cmp_ref_sorting(struct ref_sorting *s, struct ref_array_item *a, stru
 
 	get_ref_atom_value(a, s->atom, &va);
 	get_ref_atom_value(b, s->atom, &vb);
-	switch (cmp_type) {
+	if (s->version)
-	case FIELD_STR:
+		cmp = versioncmp(va->s, vb->s);
+	else if (cmp_type == FIELD_STR)
 		cmp = strcmp(va->s, vb->s);
-		break;
+	else {
-	default:
 		if (va->ul < vb->ul)
 			cmp = -1;
 		else if (va->ul == vb->ul)
 			cmp = 0;
 		else
 			cmp = 1;
-		break;
 	}
+
 	return (s->reverse) ? -cmp : cmp;
 }
 
@@ -1584,6 +1586,9 @@ int parse_opt_ref_sorting(const struct option *opt, const char *arg, int unset)
 		s->reverse = 1;
 		arg++;
 	}
+	if (skip_prefix(arg, "version:", &arg) ||
+	    skip_prefix(arg, "v:", &arg))
+		s->version = 1;
 	len = strlen(arg);
 	s->atom = parse_ref_filter_atom(arg, arg+len);
 	return 0;

ref-filter.h

@@ -28,7 +28,8 @@ struct atom_value;
 struct ref_sorting {
 	struct ref_sorting *next;
 	int atom; /* index into used_atom array (internal) */
-	unsigned reverse : 1;
+	unsigned reverse : 1,
+		version : 1;
 };
 
 struct ref_array_item {

t/t6302-for-each-ref-filter.sh

@@ -219,4 +219,40 @@ test_expect_success '`%(contents:lines=-1)` should fail' '
 	test_must_fail git for-each-ref --format="%(refname:short) |%(contents:lines=-1)"
 '
 
+test_expect_success 'setup for version sort' '
+	test_commit foo1.3 &&
+	test_commit foo1.6 &&
+	test_commit foo1.10
+'
+
+test_expect_success 'version sort' '
+	git for-each-ref --sort=version:refname --format="%(refname:short)" refs/tags/ | grep "foo" >actual &&
+	cat >expect <<-\EOF &&
+	foo1.3
+	foo1.6
+	foo1.10
+	EOF
+	test_cmp expect actual
+'
+
+test_expect_success 'version sort (shortened)' '
+	git for-each-ref --sort=v:refname --format="%(refname:short)" refs/tags/ | grep "foo" >actual &&
+	cat >expect <<-\EOF &&
+	foo1.3
+	foo1.6
+	foo1.10
+	EOF
+	test_cmp expect actual
+'
+
+test_expect_success 'reverse version sort' '
+	git for-each-ref --sort=-version:refname --format="%(refname:short)" refs/tags/ | grep "foo" >actual &&
+	cat >expect <<-\EOF &&
+	foo1.10
+	foo1.6
+	foo1.3
+	EOF
+	test_cmp expect actual
+'
+
 test_done