sphinxext: Fix duplicated output in FunctionDocumenter

Sphinx calls get_doc() multiple times per documenter: once in
_generate() to check for mocked objects, once from _find_signature()
during format_signature(), and once from add_content(). The
DocstringSignatureMixin base class caches the result of the first call
in _new_docstrings, so subsequent calls to super().get_doc() return the
same already-mutated list.

document_function() mutates its docstrings argument in-place, injecting
type fields and prepending code sample blocks. Each additional call to
FunctionDocumenter.get_doc() passed the already-mutated cached list back
through document_function(), compounding the mutations and producing
duplicated parameter samples, return samples, and return type entries in
the rendered output.

Fix by caching the result of document_function() in _wsme_docstrings and
returning it directly on subsequent calls, so document_function() is
only invoked once per documenter instance.

Change-Id: I6be82d451c3ec9aa7bf3e04cdd2642778c98da84
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Signed-off-by: Stephen Finucane <sfinucan@redhat.com>

wsmeext/sphinxext.py

@@ -519,15 +519,19 @@ class FunctionDocumenter(autodoc.MethodDocumenter):
     def get_doc(self):
         """Inject the type and param fields into the docstrings so that the
         user can add its own param fields to document the parameters"""
+        if hasattr(self, '_wsme_docstrings'):
+            return self._wsme_docstrings
+
         docstrings = super().get_doc()
 
         protocols = get_protocols(
             self.options.protocols or self.env.app.config.wsme_protocols
         )
 
-        return document_function(
+        self._wsme_docstrings = document_function(
             self.wsme_fd, docstrings, protocols
         )
+        return self._wsme_docstrings
 
     def add_content(self, more_content):
         super(FunctionDocumenter, self).add_content(more_content)