Use label to populate image release

When release for an image is specified as explicit `None`, we can
generate the value based on compose label. For example for `Alpha-1.2`
the release would be `1.2` instead of the date based one.

Signed-off-by: Lubomír Sedlář <lsedlar@redhat.com>

pungi/compose.py

@@ -344,7 +344,14 @@ class Compose(kobo.log.LoggingBase):
 
     @property
     def image_release(self):
-        """Generate a value to pass to Koji as image release. This includes
+        """Generate a value to pass to Koji as image release.
-        date, compose type and respin."""
+
+        If this compose has a label, the version from it will be used,
+        otherwise we will create a string with date, compose type and respin.
+        """
+        if self.compose_label:
+            milestone, release = self.compose_label.split('-')
+            return release
+
         return '%s%s.%s' % (self.compose_date, self.ci_base.compose.type_suffix,
                             self.compose_respin)

tests/test_compose.py

@@ -115,6 +115,7 @@ class ComposeTestCase(unittest.TestCase):
         ci.return_value.compose.date = '20160107'
         ci.return_value.compose.type = 'nightly'
         ci.return_value.compose.type_suffix = '.n'
+        ci.return_value.compose.label = None
 
         compose = Compose(conf, self.tmp_dir)
 
@@ -127,11 +128,25 @@ class ComposeTestCase(unittest.TestCase):
         ci.return_value.compose.date = '20160107'
         ci.return_value.compose.type = 'production'
         ci.return_value.compose.type_suffix = '.n'
+        ci.return_value.compose.label = None
 
         compose = Compose(conf, self.tmp_dir)
 
         self.assertEqual(compose.image_release, '20160107.n.2')
 
+    @mock.patch('pungi.compose.ComposeInfo')
+    def test_image_release_from_label(self, ci):
+        conf = {}
+        ci.return_value.compose.respin = 2
+        ci.return_value.compose.date = '20160107'
+        ci.return_value.compose.type = 'production'
+        ci.return_value.compose.type_suffix = '.n'
+        ci.return_value.compose.label = 'Alpha-1.2'
+
+        compose = Compose(conf, self.tmp_dir)
+
+        self.assertEqual(compose.image_release, '1.2')
+
     @mock.patch('pungi.compose.ComposeInfo')
     def test_get_variant_arches_without_filter(self, ci):
         conf = ConfigWrapper(