distro: add new 'ID.Version()` method

This commit adds a new method `ID.Version()` that returns a
`go-version.Version` object so that we can easily sort the distro
versions.

The `ID.Version()` currently also has to return an error because
the ID struct exposes MajorVersion/MinorVersion which means that
during the lifetime the Version may become invalid even after
`ParseID` was run. We could fix this by making {Major,Minor}Version
getters instead of the current way. Then we could also use the
version.NewVersion() library directy to parse the version string
from the ID and support things like `-beta` or other extras that
semantic versioning allows. But then that may interfere with the
distroid.Parser interface so definitely needs some more thinking.

pkg/distro/id.go

@@ -4,6 +4,8 @@ import (
 	"fmt"
 	"strconv"
 	"strings"
+
+	"github.com/hashicorp/go-version"
 )
 
 // ID represents a distro name and version
@@ -22,6 +24,16 @@ func (id ID) String() string {
 	return fmt.Sprintf("%s-%d.%d", id.Name, id.MajorVersion, id.MinorVersion)
 }
 
+func (id ID) Version() (*version.Version, error) {
+	var verStr string
+	if id.MinorVersion == -1 {
+		verStr = fmt.Sprintf("%d", id.MajorVersion)
+	} else {
+		verStr = fmt.Sprintf("%d.%d", id.MajorVersion, id.MinorVersion)
+	}
+	return version.NewVersion(verStr)
+}
+
 type ParseError struct {
 	ToParse string
 	Msg     string

pkg/distro/id_test.go

@@ -101,6 +101,13 @@ func TestDistroIDParser(t *testing.T) {
 			assert.NoError(t, err)
 			assert.NotNil(t, id)
 			assert.Equal(t, tc.expected, id)
+
+			ver, err := id.Version()
+			assert.NoError(t, err)
+			assert.Equal(t, ver.Segments()[0], tc.expected.MajorVersion)
+			if tc.expected.MinorVersion > -1 {
+				assert.Equal(t, ver.Segments()[1], tc.expected.MinorVersion)
+			}
 		})
 	}