MAINT: pick up types from core/numerictypes.pyi (#83)

Closes #65.

The types currently aren't picked up. Fix that by moving them into
`__init__.pyi` along with the rest of the types. While we are at it,
polish the signatures a bit and add tests.

Author: person142

Diff for: numpy-stubs/__init__.pyi

@@ -796,6 +796,29 @@ class AxisError(ValueError, IndexError):
         self, axis: int, ndim: Optional[int] = ..., msg_prefix: Optional[str] = ...
     ) -> None: ...
 
+# Functions from np.core.numerictypes
+_DefaultType = TypeVar("_DefaultType")
+
+def maximum_sctype(t: DtypeLike) -> dtype: ...
+def issctype(rep: object) -> bool: ...
+@overload
+def obj2sctype(rep: object) -> Optional[generic]: ...
+@overload
+def obj2sctype(rep: object, default: None) -> Optional[generic]: ...
+@overload
+def obj2sctype(
+    rep: object, default: Type[_DefaultType]
+) -> Union[generic, Type[_DefaultType]]: ...
+def issubclass_(arg1: object, arg2: Union[object, Tuple[object, ...]]) -> bool: ...
+def issubsctype(
+    arg1: Union[ndarray, DtypeLike], arg2: Union[ndarray, DtypeLike]
+) -> bool: ...
+def issubdtype(arg1: DtypeLike, arg2: DtypeLike) -> bool: ...
+def sctype2char(sctype: object) -> str: ...
+def find_common_type(
+    array_types: Sequence[DtypeLike], scalar_types: Sequence[DtypeLike]
+) -> dtype: ...
+
 # Functions from np.core.fromnumeric
 _Mode = Literal["raise", "wrap", "clip"]
 _Order = Literal["C", "F", "A"]

Diff for: numpy-stubs/core/numerictypes.pyi

@@ -0,0 +1,13 @@
+import numpy as np
+
+# Techincally this works, but probably shouldn't. See
+#
+# https://github.com/numpy/numpy/issues/16366
+#
+np.maximum_sctype(1)  # E: incompatible type "int"
+
+np.issubsctype(1, np.int64)  # E: incompatible type "int"
+
+np.issubdtype(1, np.int64)  # E: incompatible type "int"
+
+np.find_common_type(np.int64, np.int64)  # E: incompatible type "Type[int64]"

Diff for: tests/fail/numerictypes.py

@@ -0,0 +1,29 @@
+import numpy as np
+
+np.maximum_sctype("S8")
+np.maximum_sctype(object)
+
+np.issctype(object)
+np.issctype("S8")
+
+np.obj2sctype(list)
+np.obj2sctype(list, default=None)
+np.obj2sctype(list, default=np.string_)
+
+np.issubclass_(np.int32, int)
+np.issubclass_(np.float64, float)
+np.issubclass_(np.float64, (int, float))
+
+np.issubsctype("int64", int)
+np.issubsctype(np.array([1]), np.array([1]))
+
+np.issubdtype("S1", np.string_)
+np.issubdtype(np.float64, np.float32)
+
+np.sctype2char("S1")
+np.sctype2char(list)
+
+np.find_common_type([], [np.int64, np.float32, complex])
+np.find_common_type((), (np.int64, np.float32, complex))
+np.find_common_type([np.int64, np.float32], [])
+np.find_common_type([np.float32], [np.int64, np.float64])

Diff for: tests/pass/numerictypes.py

@@ -0,0 +1,18 @@
+import numpy as np
+
+reveal_type(np.issctype(np.generic))  # E: bool
+reveal_type(np.issctype("foo"))  # E: bool
+
+reveal_type(np.obj2sctype("S8"))  # E: Union[numpy.generic, None]
+reveal_type(np.obj2sctype("S8", default=None))  # E: Union[numpy.generic, None]
+reveal_type(
+    np.obj2sctype("foo", default=int)  # E: Union[numpy.generic, Type[builtins.int*]]
+)
+
+reveal_type(np.issubclass_(np.float64, float))  # E: bool
+reveal_type(np.issubclass_(np.float64, (int, float)))  # E: bool
+
+reveal_type(np.sctype2char("S8"))  # E: str
+reveal_type(np.sctype2char(list))  # E: str
+
+reveal_type(np.find_common_type([np.int64], [np.int64]))  # E: numpy.dtype