Clarify common 500 errors

module_build_service/builder/KojiContentGenerator.py

@@ -362,7 +362,7 @@ class KojiContentGenerator(object):
                 ret["filename"] = mmd_filename
                 ret["filesize"] = len(raw_data)
                 ret["checksum"] = hashlib.md5(raw_data).hexdigest()
-        except IOError:
+        except IOError as e:
             if arch == "src":
                 # This might happen in case the Module is submitted directly
                 # using the yaml without SCM URL. This should never happen
@@ -371,7 +371,7 @@ class KojiContentGenerator(object):
                 log.warning("No modulemd.src.txt found.")
                 return
             else:
-                raise
+                raise RuntimeError("Could not read %s: %s" % (mmd_path, e))
 
         components = []
         if arch in ["noarch", "src"]:
@@ -878,7 +878,7 @@ class KojiContentGenerator(object):
                 build_info = session.CGImport(metadata, serverdir)
             except koji.GenericError as e:
                 if "Build already exists" not in str(e):
-                    raise
+                    raise RuntimeError("Build import failed: %s" % e)
                 log.warning("Failed to import content generator")
                 build_info = None
             if conf.koji_cg_tag_build:

module_build_service/builder/base.py

@@ -330,7 +330,7 @@ class GenericBuilder(six.with_metaclass(ABCMeta)):
                 state=BUILD_STATES["failed"],
                 state_reason=reason, failure_type="user")
             db_session.commit()
-            raise
+            raise RuntimeError("Failed to gather buildroot groups from SCM.")
         return groups
 
     @abstractmethod

module_build_service/common/messaging.py

@@ -48,7 +48,9 @@ def publish(topic, msg, conf, service):
         return rv
     except Exception:
         messaging_tx_failed_counter.inc()
-        raise
+        raise RuntimeError(
+            "Unable to send message to backend %r" % conf.messaging
+        )
 
 
 def _fedmsg_publish(topic, msg, conf, service):

module_build_service/common/scm.py

@@ -226,7 +226,7 @@ class SCM(object):
                         "checkout: The requested commit hash was not found within the repository. "
                         "Perhaps you forgot to push. The original message was: %s" % str(e)
                     )
-                raise
+                raise RuntimeError("Unable to checkout module from SCM: %s" % e)
 
             timestamp = SCM._run(["git", "show", "-s", "--format=%ct"], chdir=self.sourcedir)[1]
             self.version = provide_module_stream_version_from_timestamp(timestamp=timestamp)

module_build_service/scheduler/default_modules.py

@@ -182,10 +182,10 @@ def _get_default_modules(stream, default_modules_scm_url):
                     scm_obj.checkout_ref(conf.rawhide_branch)
                 else:
                     # If it's not a rawhide build, then the branch should have existed
-                    raise
+                    raise RuntimeError("Branch %s does not exist" % stream)
             else:
                 # If it's not a rawhide build, then the branch should have existed
-                raise
+                raise RuntimeError("Branch %s does not exist" % stream)
 
         idx = Modulemd.ModuleIndex.new()
         idx.update_from_defaults_directory(