config: Make pkgset_koji_tag optional

There are valid use cases for not specifying this option: specifically a
modular compose will get the tags to use from modules listed in the
variants file.

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

doc/configuration.rst

@@ -446,8 +446,9 @@ Options
 **pkgset_source** [mandatory]
     (*str*) -- "koji" (any koji instance) or "repos" (arbitrary yum repositories)
 
-**pkgset_koji_tag** [mandatory]
-    (*str|[str]*) -- tag(s) to read package set from
+**pkgset_koji_tag**
+    (*str|[str]*) -- tag(s) to read package set from. This option can be
+    omitted for modular composes.
 
 **pkgset_koji_inherit** = True
     (*bool*) -- inherit builds from parent tags; we can turn it off only if we

pungi/checks.py

@@ -1172,7 +1172,6 @@ CONFIG_DEPS = {
     },
     "pkgset_source": {
         "requires": [
-            (lambda x: x == "koji", ["pkgset_koji_tag"]),
             (lambda x: x == "repos", ["pkgset_repos"]),
         ],
         "conflicts": [

tests/test_config.py

@@ -30,7 +30,6 @@ class PkgsetConfigTestCase(ConfigTestCase):
     def test_validate_minimal_pkgset_koji(self):
         cfg = load_config(
             pkgset_source='koji',
-            pkgset_koji_tag="f25",
         )
 
         self.assertValidation(cfg)
@@ -64,8 +63,7 @@ class PkgsetConfigTestCase(ConfigTestCase):
 
         self.assertValidation(
             cfg,
-            [checks.REQUIRES.format('pkgset_source', 'koji', 'pkgset_koji_tag'),
-             checks.CONFLICTS.format('pkgset_source', 'koji', 'pkgset_repos')])
+            [checks.CONFLICTS.format('pkgset_source', 'koji', 'pkgset_repos')])
 
     def test_pkgset_multiple_koji_tags(self):
         cfg = load_config(