Fix #7993: texinfo: TypeError is raised for nested object descriptions

The texinfo writer remembers the current desc node to render
a desc_annotation node.  This makes the mechanism robust to support
nested object descriptions.

CHANGES

@@ -10,6 +10,7 @@ Incompatible changes
 Deprecated
 ----------
 
+* ``sphinx.writers.texinfo.TexinfoWriter.desc``
 * C, parsing of pre-v3 style type directives and roles, along with the options
   :confval:`c_allow_pre_v3` and :confval:`c_warn_on_allowed_pre_v3`.
 
@@ -62,6 +63,7 @@ Bugs fixed
 * #7928: py domain: failed to resolve a type annotation for the attribute
 * #7968: i18n: The content of ``math`` directive is interpreted as reST on
   translation
+* #7993: texinfo: TypeError is raised for nested object descriptions
 * #7869: :rst:role:`abbr` role without an explanation will show the explanation
   from the previous abbr role
 * C and C++, removed ``noindex`` directive option as it did

doc/extdev/deprecated.rst

@@ -26,6 +26,11 @@ The following is a list of deprecated interfaces.
      - (will be) Removed
      - Alternatives
 
+   * - ``sphinx.writers.texinfo.TexinfoWriter.desc``
+     - 3.2
+     - 5.0
+     - ``sphinx.writers.texinfo.TexinfoWriter.descs``
+
    * - The first argument for
        ``sphinx.ext.autosummary.generate.AutosummaryRenderer`` has been changed
        to Sphinx object

sphinx/writers/texinfo.py

@@ -10,14 +10,16 @@
 
 import re
 import textwrap
+import warnings
 from os import path
-from typing import Any, Dict, Iterable, Iterator, List, Pattern, Set, Tuple, Union
+from typing import Any, Dict, Iterable, Iterator, List, Optional, Pattern, Set, Tuple, Union
 from typing import cast
 
 from docutils import nodes, writers
 from docutils.nodes import Element, Node, Text
 
 from sphinx import addnodes, __display_version__
+from sphinx.deprecation import RemovedInSphinx50Warning
 from sphinx.domains import IndexEntry
 from sphinx.domains.index import IndexDomain
 from sphinx.errors import ExtensionError
@@ -189,6 +191,7 @@ class TexinfoTranslator(SphinxTranslator):
 
         self.body = []                  # type: List[str]
         self.context = []               # type: List[str]
+        self.descs = []                 # type: List[addnodes.desc]
         self.previous_section = None    # type: nodes.section
         self.section_level = 0
         self.seen_title = False
@@ -1365,12 +1368,12 @@ class TexinfoTranslator(SphinxTranslator):
 
     # -- Desc
 
-    def visit_desc(self, node: Element) -> None:
-        self.desc = node
+    def visit_desc(self, node: addnodes.desc) -> None:
+        self.descs.append(node)
         self.at_deffnx = '@deffn'
 
-    def depart_desc(self, node: Element) -> None:
-        self.desc = None
+    def depart_desc(self, node: addnodes.desc) -> None:
+        self.descs.pop()
         self.ensure_eol()
         self.body.append('@end deffn\n')
 
@@ -1454,9 +1457,8 @@ class TexinfoTranslator(SphinxTranslator):
         #     -- instead of --
         #     @deffn {Class} class Foo
         txt = node.astext().strip()
-        if txt == self.desc['desctype'] or \
-           txt == self.desc['objtype'] or \
-           txt in self.desc_type_name.split():
+        if ((self.descs and txt == self.descs[-1]['objtype']) or
+                (self.desc_type_name and txt in self.desc_type_name.split())):
             raise nodes.SkipNode
 
     def depart_desc_annotation(self, node: Element) -> None:
@@ -1526,3 +1528,11 @@ class TexinfoTranslator(SphinxTranslator):
         self.body.append('\n\n@example\n%s\n@end example\n\n' %
                          self.escape_arg(node.astext()))
         raise nodes.SkipNode
+
+    @property
+    def desc(self) -> Optional[addnodes.desc]:
+        warnings.warn('TexinfoWriter.desc is deprecated.', RemovedInSphinx50Warning)
+        if len(self.descs):
+            return self.descs[-1]
+        else:
+            return None