gh-109218: Deprecate weird cases in the complex() constructor

Doc/library/functions.rst

@@ -404,6 +404,10 @@ are always available.  They are listed here in alphabetical order.
       Falls back to :meth:`~object.__index__` if :meth:`~object.__complex__` and
       :meth:`~object.__float__` are not defined.
 
+   .. deprecated:: 3.14
+      Passing a complex number as the *real* or *imag* argument is now
+      deprecated; it should only be passed as a single positional argument.
+
 
 .. function:: delattr(object, name)
 

Doc/whatsnew/3.14.rst

@@ -103,6 +103,10 @@ Optimizations
 Deprecated
 ==========
 
+* Passing a complex number as the *real* or *imag* argument in the
+  :func:`complex` constructor is now deprecated; it should only be passed
+  as a single positional argument.
+  (Contributed by Serhiy Storchaka in :gh:`109218`.)
 
 
 Removed