lib.data: at most one Union field can have annotation with a default.

2023-03-04 09:34:36 +00:00 · 2023-03-04 09:34:36 +00:00 · ae1aeff0f2
commit ae1aeff0f2
parent e2ce959c90
2 changed files with 13 additions and 0 deletions
--- a/amaranth/lib/data.py
+++ b/amaranth/lib/data.py
@ -419,6 +419,11 @@ class _AggregateMeta(ShapeCastable, type):
                if name in namespace:
                    reset[name] = namespace.pop(name)
            cls = type.__new__(metacls, name, bases, namespace)
+            if cls.__layout_cls is UnionLayout:
+                if len(reset) > 1:
+                    raise ValueError("Reset value for at most one field can be provided for "
+                                     "a union class (specified: {})"
+                                     .format(", ".join(reset.keys())))
            cls.__layout = cls.__layout_cls(layout)
            cls.__reset  = reset
            return cls