Improve constructor for builtins.dict (#8517)

Co-authored-by: Alex Waygood <Alex.Waygood@Gmail.com>

stdlib/builtins.pyi

@@ -1021,9 +1021,13 @@ class dict(MutableMapping[_KT, _VT], Generic[_KT, _VT]):
     @overload
     def __init__(self: dict[str, _VT], **kwargs: _VT) -> None: ...
     @overload
-    def __init__(self, __map: SupportsKeysAndGetItem[_KT, _VT], **kwargs: _VT) -> None: ...
+    def __init__(self, __map: SupportsKeysAndGetItem[_KT, _VT]) -> None: ...
     @overload
-    def __init__(self, __iterable: Iterable[tuple[_KT, _VT]], **kwargs: _VT) -> None: ...
+    def __init__(self: dict[str, _VT], __map: SupportsKeysAndGetItem[str, _VT], **kwargs: _VT) -> None: ...
+    @overload
+    def __init__(self, __iterable: Iterable[tuple[_KT, _VT]]) -> None: ...
+    @overload
+    def __init__(self: dict[str, _VT], __iterable: Iterable[tuple[str, _VT]], **kwargs: _VT) -> None: ...
     # Next overload is for dict(string.split(sep) for string in iterable)
     # Cannot be Iterable[Sequence[_T]] or otherwise dict(["foo", "bar", "baz"]) is not an error
     @overload

stdlib/collections/__init__.pyi

@@ -41,9 +41,13 @@ class UserDict(MutableMapping[_KT, _VT], Generic[_KT, _VT]):
     @overload
     def __init__(self: UserDict[str, _VT], __dict: None = ..., **kwargs: _VT) -> None: ...
     @overload
-    def __init__(self, __dict: SupportsKeysAndGetItem[_KT, _VT], **kwargs: _VT) -> None: ...
+    def __init__(self, __dict: SupportsKeysAndGetItem[_KT, _VT]) -> None: ...
     @overload
-    def __init__(self, __iterable: Iterable[tuple[_KT, _VT]], **kwargs: _VT) -> None: ...
+    def __init__(self: UserDict[str, _VT], __dict: SupportsKeysAndGetItem[str, _VT], **kwargs: _VT) -> None: ...
+    @overload
+    def __init__(self, __iterable: Iterable[tuple[_KT, _VT]]) -> None: ...
+    @overload
+    def __init__(self: UserDict[str, _VT], __iterable: Iterable[tuple[str, _VT]], **kwargs: _VT) -> None: ...
     @overload
     def __init__(self: UserDict[str, str], __iterable: Iterable[list[str]]) -> None: ...
     def __len__(self) -> int: ...

stdlib/multiprocessing/managers.pyi

@@ -183,9 +183,13 @@ class SyncManager(BaseManager):
     @overload
     def dict(self, **kwargs: _VT) -> DictProxy[str, _VT]: ...
     @overload
-    def dict(self, __map: SupportsKeysAndGetItem[_KT, _VT], **kwargs: _VT) -> DictProxy[_KT, _VT]: ...
+    def dict(self, __map: SupportsKeysAndGetItem[_KT, _VT]) -> DictProxy[_KT, _VT]: ...
     @overload
-    def dict(self, __iterable: Iterable[tuple[_KT, _VT]], **kwargs: _VT) -> DictProxy[_KT, _VT]: ...
+    def dict(self, __map: SupportsKeysAndGetItem[str, _VT], **kwargs: _VT) -> DictProxy[str, _VT]: ...
+    @overload
+    def dict(self, __iterable: Iterable[tuple[_KT, _VT]]) -> DictProxy[_KT, _VT]: ...
+    @overload
+    def dict(self, __iterable: Iterable[tuple[str, _VT]], **kwargs: _VT) -> DictProxy[str, _VT]: ...
     @overload
     def dict(self, __iterable: Iterable[list[str]]) -> DictProxy[str, str]: ...
     @overload

test_cases/stdlib/builtins/test_dict.py

@@ -0,0 +1,49 @@
+# pyright: reportUnnecessaryTypeIgnoreComment=true
+
+from typing import Dict, Generic, Iterable, Tuple, TypeVar
+from typing_extensions import assert_type
+
+# These do follow `__init__` overloads order:
+# mypy and pyright have different opinions about this one:
+# mypy raises: 'Need type annotation for "bad"'
+# pyright is fine with it.
+# bad = dict()
+good: Dict[str, str] = dict()
+assert_type(good, Dict[str, str])
+
+assert_type(dict(arg=1), Dict[str, int])
+
+_KT = TypeVar("_KT")
+_VT = TypeVar("_VT")
+
+
+class KeysAndGetItem(Generic[_KT, _VT]):
+    def keys(self) -> Iterable[_KT]:
+        ...
+
+    def __getitem__(self, __k: _KT) -> _VT:
+        ...
+
+
+kt1: KeysAndGetItem[int, str] = KeysAndGetItem()
+assert_type(dict(kt1), Dict[int, str])
+dict(kt1, arg="a")  # type: ignore
+
+kt2: KeysAndGetItem[str, int] = KeysAndGetItem()
+assert_type(dict(kt2, arg=1), Dict[str, int])
+
+
+def test_iterable_tuple_overload(x: Iterable[Tuple[int, str]]) -> Dict[int, str]:
+    return dict(x)
+
+
+i1: Iterable[Tuple[int, str]] = [(1, "a"), (2, "b")]
+test_iterable_tuple_overload(i1)
+dict(i1, arg="a")  # type: ignore
+
+i2: Iterable[Tuple[str, int]] = [("a", 1), ("b", 2)]
+assert_type(dict(i2, arg=1), Dict[str, int])
+
+i3: Iterable[str] = ["a.b"]
+assert_type(dict(string.split(".") for string in i3), Dict[str, str])
+dict(["foo", "bar", "baz"])  # type: ignore