Add a benchmark for nested schemas from #1097.

Author: Julian

jsonschema/benchmarks/nested_schemas.py

@@ -0,0 +1,56 @@
+"""
+Validating highly nested schemas shouldn't cause exponential time blowups.
+
+See https://github.com/python-jsonschema/jsonschema/issues/1097.
+"""
+from itertools import cycle
+
+from jsonschema.validators import validator_for
+
+metaschemaish = {
+    "$id": "https://example.com/draft/2020-12/schema/strict",
+    "$schema": "https://json-schema.org/draft/2020-12/schema",
+
+    "$vocabulary": {
+        "https://json-schema.org/draft/2020-12/vocab/core": True,
+        "https://json-schema.org/draft/2020-12/vocab/applicator": True,
+        "https://json-schema.org/draft/2020-12/vocab/unevaluated": True,
+        "https://json-schema.org/draft/2020-12/vocab/validation": True,
+        "https://json-schema.org/draft/2020-12/vocab/meta-data": True,
+        "https://json-schema.org/draft/2020-12/vocab/format-annotation": True,
+        "https://json-schema.org/draft/2020-12/vocab/content": True
+    },
+    "$dynamicAnchor": "meta",
+
+    "$ref": "https://json-schema.org/draft/2020-12/schema",
+    "unevaluatedProperties": False,
+}
+
+
+def nested_schema(levels):
+    """
+    Produce a schema which validates deeply nested objects and arrays.
+    """
+
+    names = cycle(["foo", "bar", "baz", "quux", "spam", "eggs"])
+    schema = {"type": "object", "properties": {"ham": {"type": "string"}}}
+    for _, name in zip(range(levels - 1), names):
+        schema = {"type": "object", "properties": {name: schema}}
+    return schema
+
+
+validator = validator_for(metaschemaish)(metaschemaish)
+
+if __name__ == "__main__":
+    from pyperf import Runner
+    runner = Runner()
+
+    not_nested = nested_schema(levels=1)
+    runner.bench_func("not nested", lambda: validator.is_valid(not_nested))
+
+    for levels in range(1, 11, 3):
+        schema = nested_schema(levels=levels)
+        runner.bench_func(
+            f"nested * {levels}",
+            lambda schema=schema: validator.is_valid(schema),
+        )