Merge not schemas

Author: Zac-HD

src/hypothesis_jsonschema/_canonicalise.py

@@ -757,8 +757,10 @@ def merged(schemas: List[Any]) -> Optional[Schema]:
             if m == out["contains"] or m == s["contains"]:
                 out["contains"] = m
                 s.pop("contains")
+        if "not" in out and "not" in s and out["not"] != s["not"]:
+            out["not"] = {"anyOf": [out["not"], s.pop("not")]}
+
         # TODO: merge `items` schemas or lists-of-schemas
-        # TODO: merge `not` schemas as {not: anyOf: [not1, not2]}
         # TODO: merge if/then/else schemas to the chained form
         #       or maybe canonicalise them to an anyOf instead?
         # TODO: merge dependencies

tests/test_canonicalise.py

@@ -342,6 +342,10 @@ def test_canonicalises_to_expected(schema, expected):
             ],
             {"type": "array", "contains": {"type": "integer"}, "minItems": 1},
         ),
+        (
+            [{"not": {"enum": [1, 2, 3]}}, {"not": {"enum": ["a", "b", "c"]}}],
+            {"not": {"anyOf": [{"enum": ["a", "b", "c"]}, {"enum": [1, 2, 3]}]}},
+        ),
     ]
     + [
         ([{lo: 0, hi: 9}, {lo: 1, hi: 10}], {lo: 1, hi: 9})