More object canonicalisation

Fixes #92

Author: Zac-HD

src/hypothesis_jsonschema/_canonicalise.py

@@ -391,7 +391,13 @@ def canonicalish(schema: JSONType) -> Dict[str, Any]:
     ):
         max_props = schema.get("maxProperties", math.inf)
         assert isinstance(max_props, (int, float))
+        for k, v in list(schema["properties"].items()):
+            if v == FALSEY:
+                schema["properties"].pop(k)
         schema["maxProperties"] = min(max_props, len(schema["properties"]))
+    if schema.get("maxProperties", math.inf) == 0:
+        for k in ("properties", "patternProperties", "additionalProperties"):
+            schema.pop(k, None)
     if "object" in type_ and schema.get("minProperties", 0) > schema.get(
         "maxProperties", math.inf
     ):

tests/test_canonicalise.py

@@ -305,6 +305,27 @@ def test_canonicalises_to_empty(schema):
             {"type": "integer", "allOf": [{"multipleOf": 0.5}, {"multipleOf": 1e308}]},
             {"type": "integer", "multipleOf": 1e308},
         ),
+        (
+            {
+                "additionalProperties": {"not": {}},
+                "properties": {"a": {"not": {}}},
+                "type": "object",
+            },
+            {"maxProperties": 0, "type": "object"},
+        ),
+        (
+            {
+                "additionalProperties": {"not": {}},
+                "properties": {"a": {"not": {}}, "b": {}},
+                "type": "object",
+            },
+            {
+                "additionalProperties": {"not": {}},
+                "properties": {"b": {}},
+                "maxProperties": 1,
+                "type": "object",
+            },
+        ),
     ],
 )
 def test_canonicalises_to_expected(schema, expected):