Merge branch 'master' into changelog_issue

.github/workflows/docs.yml

@@ -36,7 +36,7 @@ jobs:
       - uses: actions/checkout@v4
       - uses: actions/setup-python@v5
         with:
-          python-version: '3.8'
+          python-version: '3.12'
       - name: Install tox
         run: pip install tox==4.11.0
       - name: Setup tox environment

misc/typeshed_patches/0001-Revert-sum-literal-integer-change-13961.patch

@@ -1,4 +1,4 @@
-From 44bc98bd50e7170887f0740b53ed95a8eb04f00e Mon Sep 17 00:00:00 2001
+From 58c6a6ab863c1c38e95ccafaf13792ed9c00e499 Mon Sep 17 00:00:00 2001
 From: Shantanu <[email protected]>
 Date: Sat, 29 Oct 2022 12:47:21 -0700
 Subject: [PATCH] Revert sum literal integer change (#13961)
@@ -19,18 +19,18 @@ within mypy, I might pursue upstreaming this in typeshed.
  1 file changed, 1 insertion(+), 1 deletion(-)
 
 diff --git a/mypy/typeshed/stdlib/builtins.pyi b/mypy/typeshed/stdlib/builtins.pyi
-index 99919c64c..680cd5561 100644
+index ea9f8c894..a6065cc67 100644
 --- a/mypy/typeshed/stdlib/builtins.pyi
 +++ b/mypy/typeshed/stdlib/builtins.pyi
-@@ -1596,7 +1596,7 @@ _SupportsSumNoDefaultT = TypeVar("_SupportsSumNoDefaultT", bound=_SupportsSumWit
+@@ -1653,7 +1653,7 @@ _SupportsSumNoDefaultT = TypeVar("_SupportsSumNoDefaultT", bound=_SupportsSumWit
  # without creating many false-positive errors (see #7578).
  # Instead, we special-case the most common examples of this: bool and literal integers.
  @overload
--def sum(iterable: Iterable[bool | _LiteralInteger], /, start: int = 0) -> int: ...  # type: ignore[overload-overlap]
-+def sum(iterable: Iterable[bool], /, start: int = 0) -> int: ...  # type: ignore[overload-overlap]
+-def sum(iterable: Iterable[bool | _LiteralInteger], /, start: int = 0) -> int: ...
++def sum(iterable: Iterable[bool], /, start: int = 0) -> int: ...
  @overload
  def sum(iterable: Iterable[_SupportsSumNoDefaultT], /) -> _SupportsSumNoDefaultT | Literal[0]: ...
  @overload
 -- 
-2.39.3 (Apple Git-146)
+2.46.0
 

mypy/typeops.py

@@ -114,7 +114,11 @@ def tuple_fallback(typ: TupleType) -> Instance:
         else:
             items.append(item)
     return Instance(
-        info, [make_simplified_union(items)], extra_attrs=typ.partial_fallback.extra_attrs
+        info,
+        # Note: flattening recursive unions is dangerous, since it can fool recursive
+        # types optimization in subtypes.py and go into infinite recursion.
+        [make_simplified_union(items, handle_recursive=False)],
+        extra_attrs=typ.partial_fallback.extra_attrs,
     )
 
 
@@ -440,6 +444,7 @@ def make_simplified_union(
     *,
     keep_erased: bool = False,
     contract_literals: bool = True,
+    handle_recursive: bool = True,
 ) -> ProperType:
     """Build union type with redundant union items removed.
 
@@ -465,7 +470,7 @@ def make_simplified_union(
     to_union().
     """
     # Step 1: expand all nested unions
-    items = flatten_nested_unions(items)
+    items = flatten_nested_unions(items, handle_recursive=handle_recursive)
 
     # Step 2: fast path for single item
     if len(items) == 1:

mypy/types.py

@@ -3629,7 +3629,7 @@ def extend_args_for_prefix_and_suffix(
 
 
 def flatten_nested_unions(
-    types: Sequence[Type], handle_type_alias_type: bool = True
+    types: Sequence[Type], *, handle_type_alias_type: bool = True, handle_recursive: bool = True
 ) -> list[Type]:
     """Flatten nested unions in a type list."""
     if not isinstance(types, list):
@@ -3643,7 +3643,13 @@ def flatten_nested_unions(
 
     flat_items: list[Type] = []
     for t in typelist:
-        tp = get_proper_type(t) if handle_type_alias_type else t
+        if handle_type_alias_type:
+            if not handle_recursive and isinstance(t, TypeAliasType) and t.is_recursive:
+                tp: Type = t
+            else:
+                tp = get_proper_type(t)
+        else:
+            tp = t
         if isinstance(tp, ProperType) and isinstance(tp, UnionType):
             flat_items.extend(
                 flatten_nested_unions(tp.items, handle_type_alias_type=handle_type_alias_type)