Resolve git branches in scm_dict

If the config uses SCM dicts that include branch or tag names, they will
be resolved to specific commit ids.

It goes through the caching resolver. The main motivation for that is to
correctly support the --offline flag. It's highly unlikely there will be
two scm_dicts in the config with the same repo.

JIRA: COMPOSE-3279
Signed-off-by: Lubomír Sedlář <lsedlar@redhat.com>

pungi/checks.py

@@ -293,6 +293,21 @@ def _extend_with_default_and_alias(validator_class, offline=False):
                 except util.GitUrlResolveError as exc:
                     yield ConfigOptionError(exc)
 
+            # Resolve branch in scm dicts.
+            if (
+                # Schema says it can be an scm dict
+                subschema.get("$ref") == "#/definitions/str_or_scm_dict"
+                # and the data is actually a dict
+                and isinstance(instance.get(property), dict)
+                # and it's git
+                and instance[property]["scm"] == "git"
+                # and there's a repo URL specified
+                and "repo" in instance[property]
+            ):
+                instance[property]["branch"] = util.resolve_git_ref(
+                    instance[property]["repo"], instance[property].get("branch", "HEAD")
+                )
+
         for error in _hook_errors(properties, instance, schema):
             yield error