Canonicalise anyOf special cases when all subschemas have only the type keyword

Author: Stranger6667

CHANGELOG.md

@@ -1,5 +1,7 @@
 # Changelog
 
+- Canonicalise `anyOf` special cases when all subschemas have only the `type` keyword
+
 #### 0.18.0 - 2020-09-10
 - Performance improvements from careful caching (#62)
 - Use a validator that corresponds to the input schema draft version (#66)

src/hypothesis_jsonschema/_canonicalise.py

@@ -511,6 +511,21 @@ def canonicalish(schema: JSONType) -> Dict[str, Any]:
             return FALSEY
         if len(schema) == len(schema["anyOf"]) == 1:
             return schema["anyOf"][0]  # type: ignore
+        types = []
+        # Turn
+        #   {"anyOf": [{"type": "string"}, {"type": "null"}]}
+        # into
+        #   {"type": ["string", "null"]}
+        for subschema in schema["anyOf"]:
+            if "type" in subschema and len(subschema) == 1:
+                types.extend(get_type(subschema))
+            else:
+                break
+        else:
+            # All subschemas have only the "type" keyword, then we merge all types into the parent schema
+            del schema["anyOf"]
+            new_types = canonicalish({"type": types})
+            schema = merged([schema, new_types])
     if "allOf" in schema:
         schema["allOf"] = [
             json.loads(enc)

tests/test_canonicalise.py

@@ -200,8 +200,26 @@ def test_canonicalises_to_empty(schema):
                     {"anyOf": [{"type": "number"}, {"type": "array"}]},
                 ]
             },
-            # TODO: collapse into {"type": ["string", "number", "array"]}
-            {"anyOf": [{"type": "array"}, {"type": "number"}, {"type": "string"}]},
+            {"type": ["number", "string", "array"]},
+        ),
+        (
+            {
+                "anyOf": [
+                    {"type": "integer"},
+                    {"type": "number"},
+                ]
+            },
+            {"type": "number"},
+        ),
+        (
+            {
+                "anyOf": [
+                    {"type": "string"},
+                    {"type": "number"},
+                ],
+                "type": ["string", "object"],
+            },
+            {"type": "string"},
         ),
         ({"uniqueItems": False}, {}),
         (