Enable recursive type definitions (#218)

Author: yilinjuang

src/graphql/language/visitor.py

@@ -162,7 +162,7 @@ class Stack(NamedTuple):
     idx: int
     keys: tuple[Node, ...]
     edits: list[tuple[int | str, Node]]
-    prev: Any  # 'Stack' (python/mypy/issues/731)
+    prev: Stack
 
 
 def visit(

src/graphql/pyutils/path.py

@@ -2,15 +2,15 @@
 
 from __future__ import annotations
 
-from typing import Any, NamedTuple
+from typing import NamedTuple
 
 __all__ = ["Path"]
 
 
 class Path(NamedTuple):
     """A generic path of string or integer indices"""
 
-    prev: Any  # Optional['Path'] (python/mypy/issues/731)
+    prev: Path | None
     """path with the previous indices"""
     key: str | int
     """current index in the path (string or integer)"""
@@ -25,7 +25,7 @@ def as_list(self) -> list[str | int]:
         """Return a list of the path keys."""
         flattened: list[str | int] = []
         append = flattened.append
-        curr: Path = self
+        curr: Path | None = self
         while curr:
             append(curr.key)
             curr = curr.prev

src/graphql/validation/rules/overlapping_fields_can_be_merged.py

@@ -38,8 +38,6 @@
     from typing_extensions import TypeAlias
 
 
-MYPY = False
-
 __all__ = ["OverlappingFieldsCanBeMergedRule"]
 
 
@@ -98,10 +96,7 @@ def enter_selection_set(self, selection_set: SelectionSetNode, *_args: Any) -> N
 # Field name and reason.
 ConflictReason: TypeAlias = Tuple[str, "ConflictReasonMessage"]
 # Reason is a string, or a nested list of conflicts.
-if MYPY:  # recursive types not fully supported yet (/python/mypy/issues/731)
-    ConflictReasonMessage: TypeAlias = Union[str, List]
-else:
-    ConflictReasonMessage: TypeAlias = Union[str, List[ConflictReason]]
+ConflictReasonMessage: TypeAlias = Union[str, List[ConflictReason]]
 # Tuple defining a field node in a context.
 NodeAndDef: TypeAlias = Tuple[GraphQLCompositeType, FieldNode, Optional[GraphQLField]]
 # Dictionary of lists of those.

tests/execution/test_executor.py

@@ -308,9 +308,11 @@ def resolve_type(_val, _info, _type):
         prev, key, typename = path
         assert key == "l2"
         assert typename == "SomeObject"
+        assert prev is not None
         prev, key, typename = prev
         assert key == 0
         assert typename is None
+        assert prev is not None
         prev, key, typename = prev
         assert key == "l1"
         assert typename == "SomeQuery"