Add back comments to builtins

stdlib/builtins.pyi

@@ -101,6 +101,8 @@ class object:
     def __format__(self, __format_spec: str) -> str: ...
     def __getattribute__(self, __name: str) -> Any: ...
     def __sizeof__(self) -> int: ...
+    # return type of pickle methods is rather hard to express in the current type system
+    # see #6661 and https://docs.python.org/3/library/pickle.html#object.__reduce__
     def __reduce__(self) -> str | tuple[Any, ...]: ...
     if sys.version_info >= (3, 8):
         def __reduce_ex__(self, __protocol: SupportsIndex) -> str | tuple[Any, ...]: ...
@@ -258,6 +260,8 @@ class int:
     def __pow__(self, __x: _PositiveInteger, __modulo: None = ...) -> int: ...
     @overload
     def __pow__(self, __x: _NegativeInteger, __modulo: None = ...) -> float: ...
+    # positive x -> int; negative x -> float
+    # return type must be Any as `int | float` causes too many false-positive errors
     @overload
     def __pow__(self, __x: int, __modulo: None = ...) -> Any: ...
     def __rpow__(self, __x: int, __mod: int | None = ...) -> Any: ...
@@ -313,6 +317,8 @@ class float:
     def __divmod__(self, __x: float) -> tuple[float, float]: ...
     @overload
     def __pow__(self, __x: int, __mod: None = ...) -> float: ...
+    # positive x -> float; negative x -> complex
+    # return type must be Any as `float | complex` causes too many false-positive errors
     @overload
     def __pow__(self, __x: float, __mod: None = ...) -> Any: ...
     def __radd__(self, __x: float) -> float: ...
@@ -322,6 +328,7 @@ class float:
     def __rtruediv__(self, __x: float) -> float: ...
     def __rmod__(self, __x: float) -> float: ...
     def __rdivmod__(self, __x: float) -> tuple[float, float]: ...
+    # Returns complex if the argument is negative.
     def __rpow__(self, __x: float, __mod: None = ...) -> Any: ...
     def __getnewargs__(self) -> tuple[float]: ...
     def __trunc__(self) -> int: ...
@@ -1411,10 +1418,15 @@ if sys.version_info >= (3, 8):
     def pow(base: int, exp: _PositiveInteger, mod: None = ...) -> int: ...  # type: ignore[misc]
     @overload
     def pow(base: int, exp: _NegativeInteger, mod: None = ...) -> float: ...  # type: ignore[misc]
+    # int base & positive-int exp -> int; int base & negative-int exp -> float
+    # return type must be Any as `int | float` causes too many false-positive errors
     @overload
     def pow(base: int, exp: int, mod: None = ...) -> Any: ...
     @overload
     def pow(base: float, exp: int, mod: None = ...) -> float: ...
+    # float base & float exp could return float or complex
+    # return type must be Any (same as complex base, complex exp),
+    # as `float | complex` causes too many false-positive errors
     @overload
     def pow(base: float, exp: complex | _SupportsSomeKindOfPow, mod: None = ...) -> Any: ...
     @overload