py domain: Allow to make a style for arguments of functions and metho…

…ds (refs: sphinx-doc#6417)

CHANGES

@@ -17,6 +17,8 @@ Incompatible changes
   :confval:`autosummary_generate_overwrite` to change the behavior
 * #5923: autodoc: the members of ``object`` class are not documented by default
   when ``:inherited-members:`` and ``:special-members:`` are given.
+* #6417: py domain: doctree of desc_parameterlist has been changed.  The
+  argument names, annotations and default values are wrapped with inline node
 
 Deprecated
 ----------
@@ -32,6 +34,7 @@ Features added
   not to document inherited members of the class and uppers
 * #6558: glossary: emit a warning for duplicated glossary entry
 * #6558: std domain: emit a warning for duplicated generic objects
+* #6417: py domain: Allow to make a style for arguments of functions and methods
 
 Bugs fixed
 ----------

sphinx/domains/python.py

@@ -26,6 +26,7 @@
 from sphinx.domains import Domain, ObjType, Index, IndexEntry
 from sphinx.environment import BuildEnvironment
 from sphinx.locale import _, __
+from sphinx.pycode.function import Signature
 from sphinx.roles import XRefRole
 from sphinx.util import logging
 from sphinx.util.docfields import Field, GroupedField, TypedField
@@ -62,6 +63,23 @@
 }
 
 
+def _parse_arglist(arglist: str) -> addnodes.desc_parameterlist:
+    """Parse a list of arguments using python parser"""
+    params = addnodes.desc_parameterlist(arglist)
+    sig = Signature('(%s)' % arglist)
+    for param in sig.parameters.values():
+        params += addnodes.desc_parameter()
+        params[-1] += nodes.inline('', param.name, classes=['argument'])
+        if param.annotation is not param.empty:
+            params[-1] += nodes.Text(': ')
+            params[-1] += nodes.inline('', param.annotation, classes=['annotation'])
+        if param.default is not param.empty:
+            params[-1] += nodes.Text(' = ')
+            params[-1] += nodes.inline('', param.default, classes=['default_value'])
+
+    return params
+
+
 def _pseudo_parse_arglist(signode: desc_signature, arglist: str) -> None:
     """"Parse" a list of arguments separated by commas.
 
@@ -284,7 +302,11 @@ def handle_signature(self, sig: str, signode: desc_signature) -> Tuple[str, str]
 
         signode += addnodes.desc_name(name, name)
         if arglist:
-            _pseudo_parse_arglist(signode, arglist)
+            try:
+                signode += _parse_arglist(arglist)
+            except RuntimeError:
+                # failed to parse arglist by python's parser
+                _pseudo_parse_arglist(signode, arglist)
         else:
             if self.needs_arglist():
                 # for callables, add an empty parameter list