Use explicit type for error extensions

Replicates graphql/graphql-js@06d9cb4

Author: Cito

src/graphql/__init__.py

@@ -46,6 +46,7 @@
 # Create, format, and print GraphQL errors.
 from .error import (
     GraphQLError,
+    GraphQLErrorExtensions,
     GraphQLFormattedError,
     GraphQLSyntaxError,
     located_error,
@@ -694,6 +695,7 @@
     "NoDeprecatedCustomRule",
     "NoSchemaIntrospectionCustomRule",
     "GraphQLError",
+    "GraphQLErrorExtensions",
     "GraphQLFormattedError",
     "GraphQLSyntaxError",
     "located_error",

src/graphql/error/__init__.py

@@ -4,14 +4,15 @@
 errors.
 """
 
-from .graphql_error import GraphQLError, GraphQLFormattedError
+from .graphql_error import GraphQLError, GraphQLErrorExtensions, GraphQLFormattedError
 
 from .syntax_error import GraphQLSyntaxError
 
 from .located_error import located_error
 
 __all__ = [
     "GraphQLError",
+    "GraphQLErrorExtensions",
     "GraphQLFormattedError",
     "GraphQLSyntaxError",
     "located_error",

src/graphql/error/graphql_error.py

@@ -14,7 +14,15 @@
     )  # noqa: F401
     from ..language.source import Source  # noqa: F401
 
-__all__ = ["GraphQLError", "GraphQLFormattedError"]
+__all__ = ["GraphQLError", "GraphQLErrorExtensions", "GraphQLFormattedError"]
+
+
+# Custom extensions
+GraphQLErrorExtensions = Dict[str, Any]
+# Use a unique identifier name for your extension, for example the name of
+# your library or project. Do not use a shortened identifier as this increases
+# the risk of conflicts. We recommend you add at most one extension key,
+# a dictionary which can contain all the values you need.
 
 
 class GraphQLFormattedError(TypedDict, total=False):
@@ -33,7 +41,7 @@ class GraphQLFormattedError(TypedDict, total=False):
     path: List[Union[str, int]]
     # Reserved for implementors to extend the protocol however they see fit,
     # and hence there are no additional restrictions on its contents.
-    extensions: Dict[str, Any]
+    extensions: GraphQLErrorExtensions
 
 
 class GraphQLError(Exception):
@@ -91,7 +99,7 @@ class GraphQLError(Exception):
     original_error: Optional[Exception]
     """The original error thrown from a field resolver during execution"""
 
-    extensions: Optional[Dict[str, Any]]
+    extensions: Optional[GraphQLErrorExtensions]
     """Extension fields to add to the formatted error"""
 
     __slots__ = (
@@ -115,7 +123,7 @@ def __init__(
         positions: Optional[Collection[int]] = None,
         path: Optional[Collection[Union[str, int]]] = None,
         original_error: Optional[Exception] = None,
-        extensions: Optional[Dict[str, Any]] = None,
+        extensions: Optional[GraphQLErrorExtensions] = None,
     ) -> None:
         super().__init__(message)
         self.message = message