Allow configuration of trailing commas in multi-line signatures

CHANGES.rst

@@ -55,6 +55,11 @@ Features added
 * #7630, #4824: autodoc: Use :file:`.pyi` type stub files
   to auto-document native modules.
   Patch by Adam Turner, partially based on work by Allie Fitter.
+* #12975: Enable configuration of trailing commas in multi-line signatures
+  in the Python and Javascript domains, via the new
+  :confval:`python_trailing_comma_in_multi_line_signatures` and
+  :confval:`javascript_trailing_comma_in_multi_line_signatures`
+  configuration options.
 
 Bugs fixed
 ----------
@@ -86,6 +91,7 @@ Bugs fixed
   before static methods, which themselves are rendered before regular
   methods and attributes.
   Patch by Bénédikt Tran.
+* #12975: Avoid rendering a trailing comma in C and C++ multi-line signatures.
 
 Testing
 -------

doc/usage/configuration.rst

@@ -4092,6 +4092,14 @@ Options for the Javascript domain
 
    .. versionadded:: 7.1
 
+.. confval:: javascript_trailing_comma_in_multi_line_signatures
+   :type: :code-py:`bool`
+   :default: :code-py:`True`
+
+   Use a trailing comma in parameter lists spanning multiple lines, if true.
+
+   .. versionadded:: 8.2
+
 
 Options for the Python domain
 -----------------------------
@@ -4181,6 +4189,14 @@ Options for the Python domain
 
    .. versionadded:: 7.1
 
+.. confval:: python_trailing_comma_in_multi_line_signatures
+   :type: :code-py:`bool`
+   :default: :code-py:`True`
+
+   Use a trailing comma in parameter lists spanning multiple lines, if true.
+
+   .. versionadded:: 8.2
+
 .. confval:: python_use_unqualified_type_names
    :type: :code-py:`bool`
    :default: :code-py:`False`

sphinx/addnodes.py

@@ -259,6 +259,8 @@ class desc_parameterlist(nodes.Part, nodes.Inline, nodes.FixedTextElement):
     As default the parameter list is written in line with the rest of the signature.
     Set ``multi_line_parameter_list = True`` to describe a multi-line parameter list.
     In that case each parameter will then be written on its own, indented line.
+    A trailing comma will be added on the last line
+    if ``multi_line_trailing_comma`` is True.
     """
 
     child_text_separator = ', '
@@ -273,6 +275,8 @@ class desc_type_parameter_list(nodes.Part, nodes.Inline, nodes.FixedTextElement)
     As default the type parameters list is written in line with the rest of the signature.
     Set ``multi_line_parameter_list = True`` to describe a multi-line type parameters list.
     In that case each type parameter will then be written on its own, indented line.
+    A trailing comma will be added on the last line
+    if ``multi_line_trailing_comma`` is True.
     """
 
     child_text_separator = ', '

sphinx/domains/javascript.py

@@ -109,6 +109,10 @@ def handle_signature(self, sig: str, signode: desc_signature) -> tuple[str, str]
             and (len(sig) > max_len > 0)
         )
 
+        trailing_comma = (
+            self.env.config.javascript_trailing_comma_in_multi_line_signatures
+        )
+
         display_prefix = self.get_display_prefix()
         if display_prefix:
             signode += addnodes.desc_annotation('', '', *display_prefix)
@@ -129,7 +133,12 @@ def handle_signature(self, sig: str, signode: desc_signature) -> tuple[str, str]
             if not arglist:
                 signode += addnodes.desc_parameterlist()
             else:
-                _pseudo_parse_arglist(signode, arglist, multi_line_parameter_list)
+                _pseudo_parse_arglist(
+                    signode,
+                    arglist,
+                    multi_line_parameter_list,
+                    trailing_comma,
+                )
         return fullname, prefix
 
     def _object_hierarchy_parts(self, sig_node: desc_signature) -> tuple[str, ...]:
@@ -564,6 +573,12 @@ def setup(app: Sphinx) -> ExtensionMetadata:
         'env',
         types=frozenset({int, type(None)}),
     )
+    app.add_config_value(
+        'javascript_trailing_comma_in_multi_line_signatures',
+        True,
+        'env',
+        types=frozenset({bool}),
+    )
     return {
         'version': 'builtin',
         'env_version': 3,

sphinx/domains/python/__init__.py

@@ -1078,6 +1078,12 @@ def setup(app: Sphinx) -> ExtensionMetadata:
         'env',
         types=frozenset({int, type(None)}),
     )
+    app.add_config_value(
+        'python_trailing_comma_in_multi_line_signatures',
+        True,
+        'env',
+        types=frozenset({bool}),
+    )
     app.add_config_value('python_display_short_literal_types', False, 'env')
     app.connect('object-description-transform', filter_meta_fields)
     app.connect('missing-reference', builtin_resolver, priority=900)

sphinx/domains/python/_annotations.py

@@ -400,11 +400,15 @@ def _pformat_token(self, tok: Token, native: bool = False) -> str:
 
 
 def _parse_type_list(
-    tp_list: str, env: BuildEnvironment, multi_line_parameter_list: bool = False
+    tp_list: str,
+    env: BuildEnvironment,
+    multi_line_parameter_list: bool = False,
+    trailing_comma: bool = True,
 ) -> addnodes.desc_type_parameter_list:
     """Parse a list of type parameters according to PEP 695."""
     type_params = addnodes.desc_type_parameter_list(tp_list)
     type_params['multi_line_parameter_list'] = multi_line_parameter_list
+    type_params['multi_line_trailing_comma'] = trailing_comma
     # formal parameter names are interpreted as type parameter names and
     # type annotations are interpreted as type parameter bound or constraints
     parser = _TypeParameterListParser(tp_list)
@@ -462,11 +466,15 @@ def _parse_type_list(
 
 
 def _parse_arglist(
-    arglist: str, env: BuildEnvironment, multi_line_parameter_list: bool = False
+    arglist: str,
+    env: BuildEnvironment,
+    multi_line_parameter_list: bool = False,
+    trailing_comma: bool = True,
 ) -> addnodes.desc_parameterlist:
     """Parse a list of arguments using AST parser"""
     params = addnodes.desc_parameterlist(arglist)
     params['multi_line_parameter_list'] = multi_line_parameter_list
+    params['multi_line_trailing_comma'] = trailing_comma
     sig = signature_from_str('(%s)' % arglist)
     last_kind = None
     for param in sig.parameters.values():
@@ -522,7 +530,10 @@ def _parse_arglist(
 
 
 def _pseudo_parse_arglist(
-    signode: desc_signature, arglist: str, multi_line_parameter_list: bool = False
+    signode: desc_signature,
+    arglist: str,
+    multi_line_parameter_list: bool = False,
+    trailing_comma: bool = True,
 ) -> None:
     """'Parse' a list of arguments separated by commas.
 
@@ -532,6 +543,7 @@ def _pseudo_parse_arglist(
     """
     paramlist = addnodes.desc_parameterlist()
     paramlist['multi_line_parameter_list'] = multi_line_parameter_list
+    paramlist['multi_line_trailing_comma'] = trailing_comma
     stack: list[Element] = [paramlist]
     try:
         for argument in arglist.split(','):

sphinx/domains/python/_object.py

@@ -310,6 +310,7 @@ def handle_signature(self, sig: str, signode: desc_signature) -> tuple[str, str]
             and (sig_len - (arglist_span[1] - arglist_span[0])) > max_len > 0
         )
 
+        trailing_comma = self.env.config.python_trailing_comma_in_multi_line_signatures
         sig_prefix = self.get_signature_prefix(sig)
         if sig_prefix:
             if type(sig_prefix) is str:
@@ -332,7 +333,10 @@ def handle_signature(self, sig: str, signode: desc_signature) -> tuple[str, str]
         if tp_list:
             try:
                 signode += _parse_type_list(
-                    tp_list, self.env, multi_line_type_parameter_list
+                    tp_list,
+                    self.env,
+                    multi_line_type_parameter_list,
+                    trailing_comma,
                 )
             except Exception as exc:
                 logger.warning(
@@ -341,19 +345,34 @@ def handle_signature(self, sig: str, signode: desc_signature) -> tuple[str, str]
 
         if arglist:
             try:
-                signode += _parse_arglist(arglist, self.env, multi_line_parameter_list)
+                signode += _parse_arglist(
+                    arglist,
+                    self.env,
+                    multi_line_parameter_list,
+                    trailing_comma,
+                )
             except SyntaxError:
                 # fallback to parse arglist original parser
                 # (this may happen if the argument list is incorrectly used
                 # as a list of bases when documenting a class)
                 # it supports to represent optional arguments (ex. "func(foo [, bar])")
-                _pseudo_parse_arglist(signode, arglist, multi_line_parameter_list)
+                _pseudo_parse_arglist(
+                    signode,
+                    arglist,
+                    multi_line_parameter_list,
+                    trailing_comma,
+                )
             except (NotImplementedError, ValueError) as exc:
                 # duplicated parameter names raise ValueError and not a SyntaxError
                 logger.warning(
                     'could not parse arglist (%r): %s', arglist, exc, location=signode
                 )
-                _pseudo_parse_arglist(signode, arglist, multi_line_parameter_list)
+                _pseudo_parse_arglist(
+                    signode,
+                    arglist,
+                    multi_line_parameter_list,
+                    trailing_comma,
+                )
         else:
             if self.needs_arglist():
                 # for callables, add an empty parameter list

sphinx/writers/html5.py

@@ -174,6 +174,7 @@ def _visit_sig_parameter_list(
         self.required_params_left = sum(self.list_is_required_param)
         self.param_separator = node.child_text_separator
         self.multi_line_parameter_list = node.get('multi_line_parameter_list', False)
+        self.trailing_comma = node.get('multi_line_trailing_comma', False)
         if self.multi_line_parameter_list:
             self.body.append('\n\n')
             self.body.append(self.starttag(node, 'dl'))
@@ -238,7 +239,8 @@ def depart_desc_parameter(self, node: Element) -> None:
                 or is_required
                 and (is_last_group or next_is_required)
             ):
-                self.body.append(self.param_separator)
+                if not is_last_group or opt_param_left_at_level or self.trailing_comma:
+                    self.body.append(self.param_separator)
                 self.body.append('</dd>\n')
 
         elif self.required_params_left:
@@ -281,19 +283,26 @@ def visit_desc_optional(self, node: Element) -> None:
 
     def depart_desc_optional(self, node: Element) -> None:
         self.optional_param_level -= 1
+        level = self.optional_param_level
         if self.multi_line_parameter_list:
-            # If it's the first time we go down one level, add the separator
-            # before the bracket.
-            if self.optional_param_level == self.max_optional_param_level - 1:
+            max_level = self.max_optional_param_level
+            len_lirp = len(self.list_is_required_param)
+            is_last_group = self.param_group_index + 1 == len_lirp
+            # If it's the first time we go down one level, add the separator before the
+            # bracket, except if this is the last parameter and the parameter list
+            # should not feature a trailing comma.
+            if level == max_level - 1 and (
+                not is_last_group or level > 0 or self.trailing_comma
+            ):
                 self.body.append(self.param_separator)
             self.body.append('<span class="optional">]</span>')
             # End the line if we have just closed the last bracket of this
             # optional parameter group.
-            if self.optional_param_level == 0:
+            if level == 0:
                 self.body.append('</dd>\n')
         else:
             self.body.append('<span class="optional">]</span>')
-        if self.optional_param_level == 0:
+        if level == 0:
             self.param_group_index += 1
 
     def visit_desc_annotation(self, node: Element) -> None:

sphinx/writers/latex.py

@@ -954,6 +954,7 @@ def _visit_sig_parameter_list(
         self.required_params_left = sum(self.list_is_required_param)
         self.param_separator = r'\sphinxparamcomma '
         self.multi_line_parameter_list = node.get('multi_line_parameter_list', False)
+        self.trailing_comma = node.get('multi_line_trailing_comma', False)
 
     def visit_desc_parameterlist(self, node: Element) -> None:
         if self.has_tp_list:
@@ -1013,7 +1014,7 @@ def _depart_sig_parameter(self, node: Element) -> None:
             if (
                 opt_param_left_at_level
                 or is_required
-                and (is_last_group or next_is_required)
+                and (next_is_required or self.trailing_comma)
             ):
                 self.body.append(self.param_separator)
 
@@ -1055,13 +1056,20 @@ def visit_desc_optional(self, node: Element) -> None:
 
     def depart_desc_optional(self, node: Element) -> None:
         self.optional_param_level -= 1
+        level = self.optional_param_level
         if self.multi_line_parameter_list:
+            max_level = self.max_optional_param_level
+            len_lirp = len(self.list_is_required_param)
+            is_last_group = self.param_group_index + 1 == len_lirp
             # If it's the first time we go down one level, add the separator before the
-            # bracket.
-            if self.optional_param_level == self.max_optional_param_level - 1:
+            # bracket, except if this is the last parameter and the parameter list
+            # should not feature a trailing comma.
+            if level == max_level - 1 and (
+                not is_last_group or level > 0 or self.trailing_comma
+            ):
                 self.body.append(self.param_separator)
         self.body.append('}')
-        if self.optional_param_level == 0:
+        if level == 0:
             self.param_group_index += 1
 
     def visit_desc_annotation(self, node: Element) -> None:

sphinx/writers/text.py

@@ -648,6 +648,7 @@ def _visit_sig_parameter_list(
         self.required_params_left = sum(self.list_is_required_param)
         self.param_separator = ', '
         self.multi_line_parameter_list = node.get('multi_line_parameter_list', False)
+        self.trailing_comma = node.get('multi_line_trailing_comma', False)
         if self.multi_line_parameter_list:
             self.param_separator = self.param_separator.rstrip()
         self.context.append(sig_close_paren)
@@ -699,7 +700,8 @@ def visit_desc_parameter(self, node: Element) -> None:
                 or is_required
                 and (is_last_group or next_is_required)
             ):
-                self.add_text(self.param_separator)
+                if not is_last_group or opt_param_left_at_level or self.trailing_comma:
+                    self.add_text(self.param_separator)
                 self.end_state(wrap=False, end=None)
 
         elif self.required_params_left:
@@ -740,20 +742,27 @@ def visit_desc_optional(self, node: Element) -> None:
 
     def depart_desc_optional(self, node: Element) -> None:
         self.optional_param_level -= 1
+        level = self.optional_param_level
         if self.multi_line_parameter_list:
+            max_level = self.max_optional_param_level
+            len_lirp = len(self.list_is_required_param)
+            is_last_group = self.param_group_index + 1 == len_lirp
             # If it's the first time we go down one level, add the separator before the
-            # bracket.
-            if self.optional_param_level == self.max_optional_param_level - 1:
+            # bracket, except if this is the last parameter and the parameter list
+            # should not feature a trailing comma.
+            if level == max_level - 1 and (
+                not is_last_group or level > 0 or self.trailing_comma
+            ):
                 self.add_text(self.param_separator)
             self.add_text(']')
             # End the line if we have just closed the last bracket of this group of
             # optional parameters.
-            if self.optional_param_level == 0:
+            if level == 0:
                 self.end_state(wrap=False, end=None)
 
         else:
             self.add_text(']')
-        if self.optional_param_level == 0:
+        if level == 0:
             self.param_group_index += 1
 
     def visit_desc_annotation(self, node: Element) -> None: