tests/hgweberror.py

cext: add Python 3.10 support

* Replace "Py_TYPE(obj) = type;" with "Py_SET_TYPE(obj, type);"
* Add pythoncapi_compat.h header file to get Py_SET_TYPE() on Python
  2.7-3.8. Header file added to mercurial/ and
  contrib/python-zstandard/zstd/common/.

In Python 3.10, Py_TYPE(obj) must not longer be used as an l-value.

pythoncapi_compat.h comes from:
https://github.com/pythoncapi/pythoncapi_compat

Differential Revision: https://phab.mercurial-scm.org/D9825

# A dummy extension that installs an hgweb command that throws an Exception.

from __future__ import absolute_import

from mercurial.hgweb import webcommands


def raiseerror(web):
    '''Dummy web command that raises an uncaught Exception.'''

    # Simulate an error after partial response.
    if b'partialresponse' in web.req.qsparams:
        web.res.status = b'200 Script output follows'
        web.res.headers[b'Content-Type'] = b'text/plain'
        web.res.setbodywillwrite()
        list(web.res.sendresponse())
        web.res.getbodyfile().write(b'partial content\n')

    raise AttributeError('I am an uncaught error!')


def extsetup(ui):
    setattr(webcommands, 'raiseerror', raiseerror)
    webcommands.__all__.append(b'raiseerror')