[3.9] bpo-40204: Allow pre-Sphinx 3 syntax in the doc (GH-21844) (GH-21901)

* bpo-40204: Allow pre-Sphinx 3 syntax in the doc (GH-21844)

Enable Sphinx 3.2 "c_allow_pre_v3" option and disable the
c_warn_on_allowed_pre_v3 option to make the documentation compatible
with Sphinx 2 and Sphinx 3.

(cherry picked from commit 423e77d6de497931585d1883805a9e3fa4096b0b)

* bpo-40204: Fix Sphinx sytanx in howto/instrumentation.rst (GH-21858)

Use generic '.. object::' to declare markers, rather than abusing
'..  c:function::' which fails on Sphinx 3.

(cherry picked from commit 43577c01a2ab49122db696e9eaec6cb31d11cc81)

* bpo-40204: Fix duplicates in the documentation (GH-21857)

Fix two Sphinx 3 issues:

Doc/c-api/buffer.rst:304: WARNING: Duplicate C declaration, also defined in 'c-api/buffer'.
Declaration is 'PyBUF_ND'.

Doc/c-api/unicode.rst:1603: WARNING: Duplicate C declaration, also defined in 'c-api/unicode'.
Declaration is 'PyObject* PyUnicode_Translate(PyObject *str, PyObject *table, const char *errors)'.

(cherry picked from commit 46d10b1237c67ff8347f533eda6a5468d098f7eb)

* bpo-40204: Add :noindex: in the documentation (GH-21859)

Add :noindex: to duplicated documentation to fix "duplicate object
description" errors.

For example, fix this Sphinx 3 issue:

Doc/library/configparser.rst:1146: WARNING: duplicate object
description of configparser.ConfigParser.optionxform, other instance
in library/configparser, use :noindex: for one of them

(cherry picked from commit d3ded080482beae578faa704b13534a62d066f9f)

* bpo-40204, doc: Fix syntax of C variables (GH-21846)

For example, fix the following Sphinx 3 errors:

Doc/c-api/buffer.rst:102: WARNING: Error in declarator or parameters
Invalid C declaration: Expected identifier in nested name. [error at 5]
  void \*obj
  -----^

Doc/c-api/arg.rst:130: WARNING: Unparseable C cross-reference: 'PyObject*'
Invalid C declaration: Expected end of definition. [error at 8]
  PyObject*
  --------^

The modified documentation is compatible with Sphinx 2 and Sphinx 3.

(cherry picked from commit 474652fe9346382dbf793f20b671eb74668bebde)

* bpo-40204: Fix reference to terms in the doc (GH-21865)

Sphinx 3 requires to refer to terms with the exact case.

For example, fix the Sphinx 3 warning:

Doc/library/pkgutil.rst:71: WARNING: term Loader not found in case
sensitive match.made a reference to loader instead.

(cherry picked from commit bb0b08540cc93e56f3f1bde1b39ce086d9e35fe1)

* bpo-40204: Fix duplicated productionlist names in the doc (GH-21900)

Sphinx 3 disallows having more than one productionlist markup with
the same name. Simply remove names in this case, since names are not
shown anyway. For example, fix the Sphinx 3 warning:

Doc/reference/introduction.rst:96: duplicate token description
of *:name, other instance in reference/expressions

(cherry picked from commit 1abeda80f760134b4233608e2c288790f955b95a)
diff --git a/Doc/c-api/buffer.rst b/Doc/c-api/buffer.rst
index fc1430e..e327193 100644
--- a/Doc/c-api/buffer.rst
+++ b/Doc/c-api/buffer.rst
@@ -89,7 +89,7 @@
 
 .. c:type:: Py_buffer
 
-   .. c:member:: void \*buf
+   .. c:member:: void *buf
 
       A pointer to the start of the logical structure described by the buffer
       fields. This can be any location within the underlying physical memory
@@ -99,7 +99,7 @@
       For :term:`contiguous` arrays, the value points to the beginning of
       the memory block.
 
-   .. c:member:: void \*obj
+   .. c:member:: void *obj
 
       A new reference to the exporting object. The reference is owned by
       the consumer and automatically decremented and set to ``NULL`` by
@@ -145,7 +145,7 @@
       or a :c:macro:`PyBUF_WRITABLE` request, the consumer must disregard
       :c:member:`~Py_buffer.itemsize` and assume ``itemsize == 1``.
 
-   .. c:member:: const char \*format
+   .. c:member:: const char *format
 
       A *NUL* terminated string in :mod:`struct` module style syntax describing
       the contents of a single item. If this is ``NULL``, ``"B"`` (unsigned bytes)
@@ -164,7 +164,7 @@
       to 64. Exporters MUST respect this limit, consumers of multi-dimensional
       buffers SHOULD be able to handle up to :c:macro:`PyBUF_MAX_NDIM` dimensions.
 
-   .. c:member:: Py_ssize_t \*shape
+   .. c:member:: Py_ssize_t *shape
 
       An array of :c:type:`Py_ssize_t` of length :c:member:`~Py_buffer.ndim`
       indicating the shape of the memory as an n-dimensional array. Note that
@@ -177,7 +177,7 @@
 
       The shape array is read-only for the consumer.
 
-   .. c:member:: Py_ssize_t \*strides
+   .. c:member:: Py_ssize_t *strides
 
       An array of :c:type:`Py_ssize_t` of length :c:member:`~Py_buffer.ndim`
       giving the number of bytes to skip to get to a new element in each
@@ -189,7 +189,7 @@
 
       The strides array is read-only for the consumer.
 
-   .. c:member:: Py_ssize_t \*suboffsets
+   .. c:member:: Py_ssize_t *suboffsets
 
       An array of :c:type:`Py_ssize_t` of length :c:member:`~Py_buffer.ndim`.
       If ``suboffsets[n] >= 0``, the values stored along the nth dimension are
@@ -207,7 +207,7 @@
 
       The suboffsets array is read-only for the consumer.
 
-   .. c:member:: void \*internal
+   .. c:member:: void *internal
 
       This is for use internally by the exporting object. For example, this
       might be re-cast as an integer by the exporter and used to store flags
@@ -301,7 +301,7 @@
 +-----------------------------------+-------+---------+------------+--------+
 | .. c:macro:: PyBUF_ANY_CONTIGUOUS |  yes  |   yes   |    NULL    | C or F |
 +-----------------------------------+-------+---------+------------+--------+
-| .. c:macro:: PyBUF_ND             |  yes  |   NULL  |    NULL    |   C    |
+| :c:macro:`PyBUF_ND`               |  yes  |   NULL  |    NULL    |   C    |
 +-----------------------------------+-------+---------+------------+--------+
 
 
@@ -438,12 +438,12 @@
 
    Send a request to *exporter* to fill in *view* as specified by  *flags*.
    If the exporter cannot provide a buffer of the exact type, it MUST raise
-   :c:data:`PyExc_BufferError`, set :c:member:`view->obj` to ``NULL`` and
+   :c:data:`PyExc_BufferError`, set ``view->obj`` to ``NULL`` and
    return ``-1``.
 
-   On success, fill in *view*, set :c:member:`view->obj` to a new reference
+   On success, fill in *view*, set ``view->obj`` to a new reference
    to *exporter* and return 0. In the case of chained buffer providers
-   that redirect requests to a single object, :c:member:`view->obj` MAY
+   that redirect requests to a single object, ``view->obj`` MAY
    refer to this object instead of *exporter* (See :ref:`Buffer Object Structures <buffer-structs>`).
 
    Successful calls to :c:func:`PyObject_GetBuffer` must be paired with calls
@@ -455,7 +455,7 @@
 .. c:function:: void PyBuffer_Release(Py_buffer *view)
 
    Release the buffer *view* and decrement the reference count for
-   :c:member:`view->obj`. This function MUST be called when the buffer
+   ``view->obj``. This function MUST be called when the buffer
    is no longer being used, otherwise reference leaks may occur.
 
    It is an error to call this function on a buffer that was not obtained via
@@ -516,9 +516,9 @@
    *view* as specified by flags, unless *buf* has been designated as read-only
    and :c:macro:`PyBUF_WRITABLE` is set in *flags*.
 
-   On success, set :c:member:`view->obj` to a new reference to *exporter* and
+   On success, set ``view->obj`` to a new reference to *exporter* and
    return 0. Otherwise, raise :c:data:`PyExc_BufferError`, set
-   :c:member:`view->obj` to ``NULL`` and return ``-1``;
+   ``view->obj`` to ``NULL`` and return ``-1``;
 
    If this function is used as part of a :ref:`getbufferproc <buffer-structs>`,
    *exporter* MUST be set to the exporting object and *flags* must be passed