bpo-37540: vectorcall: keyword names must be strings (GH-14682)

The fact that keyword names are strings is now part of the vectorcall and `METH_FASTCALL` protocols. The biggest concrete change is that `_PyStack_UnpackDict` now checks that and raises `TypeError` if not.

CC @markshannon @vstinner 


https://bugs.python.org/issue37540

3 files changed, 7 insertions, 4 deletions

diff --git a/Doc/c-api/object.rst b/Doc/c-api/object.rst
index 2cf0328..fd1e9c6 100644
--- a/Doc/c-api/object.rst
+++ b/Doc/c-api/object.rst
@@ -400,8 +400,8 @@ Object Protocol
    :c:func:`PyVectorcall_NARGS(nargsf) <PyVectorcall_NARGS>`.
 
    *kwnames* can be either NULL (no keyword arguments) or a tuple of keyword
-   names. In the latter case, the values of the keyword arguments are stored
-   in *args* after the positional arguments.
+   names, which must be strings. In the latter case, the values of the keyword
+   arguments are stored in *args* after the positional arguments.
    The number of keyword arguments does not influence *nargsf*.
 
    *kwnames* must contain only objects of type ``str`` (not a subclass),
diff --git a/Doc/c-api/structures.rst b/Doc/c-api/structures.rst
index 5184ad5..d4e65af 100644
--- a/Doc/c-api/structures.rst
+++ b/Doc/c-api/structures.rst
@@ -204,6 +204,7 @@ also keyword arguments.  So there are a total of 6 calling conventions:
    Keyword arguments are passed the same way as in the vectorcall protocol:
    there is an additional fourth :c:type:`PyObject\*` parameter
    which is a tuple representing the names of the keyword arguments
+   (which are guaranteed to be strings)
    or possibly *NULL* if there are no keywords.  The values of the keyword
    arguments are stored in the *args* array, after the positional arguments.
 
diff --git a/Doc/library/dis.rst b/Doc/library/dis.rst
index 39a3e13..4a20245 100644
--- a/Doc/library/dis.rst
+++ b/Doc/library/dis.rst
@@ -1142,8 +1142,10 @@ All of the following opcodes use their arguments.
 
    Calls a callable object with positional (if any) and keyword arguments.
    *argc* indicates the total number of positional and keyword arguments.
-   The top element on the stack contains a tuple of keyword argument names.
-   Below that are keyword arguments in the order corresponding to the tuple.
+   The top element on the stack contains a tuple with the names of the
+   keyword arguments, which must be strings.
+   Below that are the values for the keyword arguments,
+   in the order corresponding to the tuple.
    Below that are positional arguments, with the right-most parameter on
    top.  Below the arguments is a callable object to call.
    ``CALL_FUNCTION_KW`` pops all arguments and the callable object off the stack,