libs.faults: add ensure_fault_or_none() and join_faults()

libs/faults.py

@@ -1,6 +1,39 @@
 from json import loads, dumps
 
 from bundlewrap.metadata import metadata_to_json
+from bundlewrap.utils import Fault
+
 
 def resolve_faults(dictionary: dict) -> dict:
     return loads(metadata_to_json(dictionary))
+
+
+def ensure_fault_or_none(maybe_fault):
+    if maybe_fault is None or isinstance(maybe_fault, Fault):
+        return maybe_fault
+
+    return Fault(maybe_fault, lambda f: f, f=maybe_fault)
+
+
+def join_faults(faults, by=' '):
+    result = []
+    id_list = []
+
+    for item in faults:
+        result.append(ensure_fault_or_none(item))
+
+        if isinstance(item, Fault):
+            id_list += item.id_list
+        else:
+            id_list.append(item)
+
+    id_list += [
+        'joined_by',
+        by,
+    ]
+
+    return Fault(
+        id_list,
+        lambda o: by.join([i.value for i in o]),
+        o=result,
+    )