fix: ensure deterministic results for SortBySemVer() (#559)

Signed-off-by: Kent <kent.rancourt@gmail.com>

pkg/tag/semver.go

@@ -0,0 +1,31 @@
+package tag
+
+import "github.com/Masterminds/semver"
+
+// semverCollection is a replacement for semver.Collection that breaks version
+// comparison ties through a lexical comparison of the original version strings.
+// Using this, instead of semver.Collection, when sorting will yield
+// deterministic results that semver.Collection will not yield.
+type semverCollection []*semver.Version
+
+// Len returns the length of a collection. The number of Version instances
+// on the slice.
+func (s semverCollection) Len() int {
+	return len(s)
+}
+
+// Less is needed for the sort interface to compare two Version objects on the
+// slice. If checks if one is less than the other.
+func (s semverCollection) Less(i, j int) bool {
+	comp := s[i].Compare(s[j])
+	if comp != 0 {
+		return comp < 0
+	}
+	return s[i].Original() < s[j].Original()
+}
+
+// Swap is needed for the sort interface to replace the Version objects
+// at two different positions in the slice.
+func (s semverCollection) Swap(i, j int) {
+	s[i], s[j] = s[j], s[i]
+}

pkg/tag/tag.go

@@ -165,7 +165,7 @@ func (il ImageTagList) SortBySemVer() SortableImageTagList {
 		}
 		svl = append(svl, svi)
 	}
-	sort.Sort(semver.Collection(svl))
+	sort.Sort(semverCollection(svl))
 	for _, svi := range svl {
 		sil = append(sil, NewImageTag(svi.Original(), *il.items[svi.Original()].TagDate, il.items[svi.Original()].TagDigest))
 	}

pkg/tag/tag_test.go

@@ -106,7 +106,7 @@ func Test_SortableImageTagList(t *testing.T) {
 	})
 
 	t.Run("Sort by semver", func(t *testing.T) {
-		names := []string{"v2.0.2", "v1.0", "v1.0.1", "v2.0.3", "v2.0"}
+		names := []string{"v2.0.2", "v1.0", "v2.0.0", "v1.0.1", "v2.0.3", "v2.0"}
 		il := NewImageTagList()
 		for _, name := range names {
 			tag := NewImageTag(name, time.Now(), "")
@@ -117,8 +117,9 @@ func Test_SortableImageTagList(t *testing.T) {
 		assert.Equal(t, "v1.0", sil[0].TagName)
 		assert.Equal(t, "v1.0.1", sil[1].TagName)
 		assert.Equal(t, "v2.0", sil[2].TagName)
-		assert.Equal(t, "v2.0.2", sil[3].TagName)
-		assert.Equal(t, "v2.0.3", sil[4].TagName)
+		assert.Equal(t, "v2.0.0", sil[3].TagName)
+		assert.Equal(t, "v2.0.2", sil[4].TagName)
+		assert.Equal(t, "v2.0.3", sil[5].TagName)
 	})
 
 	t.Run("Sort by date", func(t *testing.T) {