make anything not acceptable to JSON as a key a compound key

autoconf/dictable.py

@@ -116,7 +116,10 @@ def to_dict(obj, filter_args: Tuple[str, ...] = ()) -> dict:
     if isinstance(obj, tuple):
         return {"type": "tuple", "values": list(map(to_dict, obj))}
     if isinstance(obj, dict):
-        if any(isinstance(key, (list, dict, tuple)) for key in obj.keys()):
+        if any(
+            not (isinstance(key, (str, int, float, bool)) or key is None)
+            for key in obj.keys()
+        ):
             return compound_key_dict(obj)
 
         return {

test_autoconf/test_dictable.py

@@ -199,3 +199,16 @@ def test_compound_key():
 
     string = json.dumps(to_dict(d))
     assert d == from_dict(json.loads(string))
+
+
+class Prior:
+    def __eq__(self, other):
+        return isinstance(other, Prior)
+
+    def __hash__(self):
+        return hash(Prior)
+
+
+def test_prior_key():
+    string = json.dumps(to_dict({Prior(): 1}))
+    assert from_dict(json.loads(string)) == {Prior(): 1}