typeddict: disallow nesting Required in itself (#2374)

Fixes #2372

Author: JelleZijlstra

conformance/results/mypy/typeddicts_required.toml

@@ -2,8 +2,8 @@ conformant = "Pass"
 output = """
 typeddicts_required.py:12: error: Required[] can be only used in a TypedDict definition  [valid-type]
 typeddicts_required.py:16: error: NotRequired[] can be only used in a TypedDict definition  [valid-type]
-typeddicts_required.py:59: error: "Required[]" type cannot be nested  [valid-type]
-typeddicts_required.py:60: error: "NotRequired[]" type cannot be nested  [valid-type]
+typeddicts_required.py:60: error: "Required[]" type cannot be nested  [valid-type]
+typeddicts_required.py:61: error: "NotRequired[]" type cannot be nested  [valid-type]
 """
 conformance_automated = "Pass"
 errors_diff = """

conformance/results/pycroscope/typeddicts_required.toml

@@ -4,6 +4,6 @@ errors_diff = """
 output = """
 ./typeddicts_required.py:12:7: Unexpected Required annotation [invalid_qualifier]
 ./typeddicts_required.py:16:7: Unexpected NotRequired annotation [invalid_qualifier]
-./typeddicts_required.py:59:16: Required[] cannot be nested [invalid_qualifier]
-./typeddicts_required.py:60:7: Required[] and NotRequired[] cannot be nested [invalid_qualifier]
+./typeddicts_required.py:60:16: Required[] cannot be nested [invalid_qualifier]
+./typeddicts_required.py:61:7: Required[] and NotRequired[] cannot be nested [invalid_qualifier]
 """

conformance/results/pyrefly/typeddicts_required.toml

@@ -6,6 +6,6 @@ output = """
 ERROR typeddicts_required.py:12:5-6: `Required` may only be used for TypedDict members [invalid-annotation]
 ERROR typeddicts_required.py:16:8-19: `NotRequired` is only allowed inside a class body [invalid-annotation]
 ERROR typeddicts_required.py:16:8-24: `NotRequired` is not allowed in this context [invalid-annotation]
-ERROR typeddicts_required.py:59:8-31: Duplicate qualifier `Required` [invalid-annotation]
-ERROR typeddicts_required.py:60:8-34: Cannot combine `Required` and `NotRequired` for a TypedDict field [invalid-annotation]
+ERROR typeddicts_required.py:60:8-31: Duplicate qualifier `Required` [invalid-annotation]
+ERROR typeddicts_required.py:61:8-34: Cannot combine `Required` and `NotRequired` for a TypedDict field [invalid-annotation]
 """

conformance/results/pyright/typeddicts_required.toml

@@ -2,8 +2,8 @@ conformant = "Pass"
 output = """
 typeddicts_required.py:12:8 - error: "Required" is not allowed in this context (reportInvalidTypeForm)
 typeddicts_required.py:16:8 - error: "NotRequired" is not allowed in this context (reportInvalidTypeForm)
-typeddicts_required.py:59:8 - error: "Required" is not allowed in this context (reportInvalidTypeForm)
 typeddicts_required.py:60:8 - error: "Required" is not allowed in this context (reportInvalidTypeForm)
+typeddicts_required.py:61:8 - error: "Required" is not allowed in this context (reportInvalidTypeForm)
 """
 conformance_automated = "Pass"
 errors_diff = """

conformance/results/ty/typeddicts_required.toml

@@ -4,6 +4,6 @@ errors_diff = """
 output = """
 typeddicts_required.py:12:8: error[invalid-type-form] `Required` is only allowed in TypedDict fields
 typeddicts_required.py:16:8: error[invalid-type-form] Type qualifier `typing.NotRequired` is not allowed in parameter annotations
-typeddicts_required.py:59:8: error[invalid-type-form] `typing.Required` cannot be nested inside `Required` or `NotRequired`
 typeddicts_required.py:60:8: error[invalid-type-form] `typing.Required` cannot be nested inside `Required` or `NotRequired`
+typeddicts_required.py:61:8: error[invalid-type-form] `typing.Required` cannot be nested inside `Required` or `NotRequired`
 """

conformance/results/zuban/typeddicts_required.toml

@@ -4,6 +4,6 @@ errors_diff = """
 output = """
 typeddicts_required.py:12: error: Required[] can be only used in a TypedDict definition  [valid-type]
 typeddicts_required.py:16: error: NotRequired[] can be only used in a TypedDict definition  [valid-type]
-typeddicts_required.py:59: error: "Required[]" type cannot be nested  [misc]
-typeddicts_required.py:60: error: "NotRequired[]" type cannot be nested  [misc]
+typeddicts_required.py:60: error: "Required[]" type cannot be nested  [misc]
+typeddicts_required.py:61: error: "NotRequired[]" type cannot be nested  [misc]
 """

conformance/tests/typeddicts_required.py

@@ -56,12 +56,13 @@ class TD5(TypedDict, total=True):
 
 
 class TD6(TypedDict):
+    # > It is also an error to nest a qualifier within itself (e.g., ``Required[Required[T]]``).
     a: Required[Required[int]]  # E: Nesting not allowed
     b: Required[NotRequired[int]]  # E: Nesting not allowed
 
 
 class TD7(TypedDict):
-    # > Required[] and NotRequired[] can be used with Annotated[], in any nesting order.
+    # > These type qualifiers may be nested arbitrarily or wrapped in ``Annotated[]``.
     x: Annotated[Required[int], ""]
     y: Required[Annotated[int, ""]]
     z: Annotated[Required[Annotated[int, ""]], ""]

docs/spec/typeddict.rst

@@ -143,6 +143,7 @@ expression contains a :term:`type expression`, optionally qualified with one of
 :term:`type qualifiers <type qualifier>` ``Required``, ``NotRequired``, or ``ReadOnly``.
 These type qualifiers may be nested arbitrarily or wrapped in ``Annotated[]``. It is
 an error to use both ``Required`` and ``NotRequired`` in the same item definition.
+It is also an error to nest a qualifier within itself (e.g., ``Required[Required[T]]``).
 An item is :term:`read-only` if and only if the ``ReadOnly`` qualifier is used.
 
 To determine whether an item is :term:`required` or :term:`non-required`, the following