ENH: enable multiline signatures when too long.

CHANGES

@@ -26,6 +26,13 @@ Features added
   generated HTML, using the CRC32 algorithm.
 * :meth:`~sphinx.application.Sphinx.require_sphinx` now allows the version
   requirement to be specified as ``(major, minor)``.
+* #11011: Allow configuring a line-length limit for object signatures, via
+  :confval:`maximum_signature_line_length` and the domain-specific variants.
+  If the length of the signature (in characters) is greater than the configured
+  limit, each parameter in the signature will be split to its own logical line.
+  This behaviour may also be controlled by options on object description
+  directives, for example :rst:dir:`py:function:single-line-parameter-list`.
+  Patch by Thomas Louf, Adam Turner, and Jean-François Burnol.
 
 Bugs fixed
 ----------

doc/latex.rst

@@ -1479,6 +1479,12 @@ Macros
   .. versionadded:: 6.2.0
      ``\sphinxparam``, ``\sphinxsamedocref``
 
+  .. versionadded:: 7.1.0
+     ``\sphinxparamcomma`` which defaults to a comma followed by a space and
+     ``\sphinxparamcommaoneperline`` which is used for one-parameter-per-line
+     signatures (see :confval:`maximum_signature_line_length`).  It defaults
+     to ``\texttt{,}`` to make these end-of-line separators more distinctive.
+
 - More text styling:
 
   .. csv-table::

doc/usage/configuration.rst

@@ -675,6 +675,25 @@ General configuration
       If the value is a fully-qualified name of a custom Pygments style class,
       this is then used as custom style.
 
+.. confval:: maximum_signature_line_length
+
+   If a signature's length in characters exceeds the number set, each
+   parameter within the signature will be displayed on an individual logical
+   line.
+
+   When ``None`` (the default), there is no maximum length and the entire
+   signature will be displayed on a single logical line.
+
+   A 'logical line' is similar to a hard line break---builders or themes may
+   choose to 'soft wrap' a single logical line, and this setting does not affect
+   that behaviour.
+
+   Domains may provide options to suppress any hard wrapping on an individual
+   object directive, such as seen in the C, C++, and Python domains (e.g.
+   :rst:dir:`py:function:single-line-parameter-list`).
+
+   .. versionadded:: 7.1
+
 .. confval:: add_function_parentheses
 
    A boolean that decides whether parentheses are appended to function and
@@ -2912,6 +2931,14 @@ Options for the C domain
 
   .. versionadded:: 4.0.3
 
+.. confval:: c_maximum_signature_line_length
+
+   If a signature's length in characters exceeds the number set, each
+   parameter will be displayed on an individual logical line. This is a
+   domain-specific setting, overriding :confval:`maximum_signature_line_length`.
+
+   .. versionadded:: 7.1
+
 .. _cpp-config:
 
 Options for the C++ domain
@@ -2942,6 +2969,14 @@ Options for the C++ domain
 
    .. versionadded:: 1.5
 
+.. confval:: cpp_maximum_signature_line_length
+
+   If a signature's length in characters exceeds the number set, each
+   parameter will be displayed on an individual logical line. This is a
+   domain-specific setting, overriding :confval:`maximum_signature_line_length`.
+
+   .. versionadded:: 7.1
+
 Options for the Python domain
 -----------------------------
 
@@ -2984,6 +3019,25 @@ Options for the Python domain
 
    .. note:: This configuration is still in experimental
 
+.. confval:: python_maximum_signature_line_length
+
+   If a signature's length in characters exceeds the number set, each
+   argument will be displayed on an individual logical line. This is a
+   domain-specific setting, overriding :confval:`maximum_signature_line_length`.
+
+   .. versionadded:: 7.1
+
+Options for the Javascript domain
+---------------------------------
+
+.. confval:: javascript_maximum_signature_line_length
+
+   If a signature's length in characters exceeds the number set, each
+   parameter will be displayed on an individual logical line. This is a
+   domain-specific setting, overriding :confval:`maximum_signature_line_length`.
+
+   .. versionadded:: 7.1
+
 Example of configuration file
 -----------------------------
 

doc/usage/restructuredtext/domains.rst

@@ -231,6 +231,16 @@ The following directives are provided for module and class contents:
       Describe the location where the object is defined.  The default value is
       the module specified by :rst:dir:`py:currentmodule`.
 
+   .. rst:directive:option:: single-line-parameter-list
+      :type: no value
+
+      Ensures that the function's arguments will be emitted on a single logical
+      line, overriding :confval:`python_maximum_signature_line_length` and
+      :confval:`maximum_signature_line_length`.
+
+      .. versionadded:: 7.1
+
+
 .. rst:directive:: .. py:data:: name
 
    Describes global data in a module, including both variables and values used
@@ -329,6 +339,15 @@ The following directives are provided for module and class contents:
       Describe the location where the object is defined.  The default value is
       the module specified by :rst:dir:`py:currentmodule`.
 
+   .. rst:directive:option:: single-line-parameter-list
+      :type: no value
+
+      Ensures that the class constructor's arguments will be emitted on a single
+      logical line, overriding :confval:`python_maximum_signature_line_length`
+      and :confval:`maximum_signature_line_length`.
+
+      .. versionadded:: 7.1
+
 .. rst:directive:: .. py:attribute:: name
 
    Describes an object data attribute.  The description should include
@@ -441,6 +460,15 @@ The following directives are provided for module and class contents:
       Describe the location where the object is defined.  The default value is
       the module specified by :rst:dir:`py:currentmodule`.
 
+   .. rst:directive:option:: single-line-parameter-list
+      :type: no value
+
+      Ensures that the method's arguments will be emitted on a single logical
+      line, overriding :confval:`python_maximum_signature_line_length` and
+      :confval:`maximum_signature_line_length`.
+
+      .. versionadded:: 7.1
+
    .. rst:directive:option:: staticmethod
       :type: no value
 
@@ -494,6 +522,15 @@ The following directives are provided for module and class contents:
    There is no ``py:deco`` role to link to a decorator that is marked up with
    this directive; rather, use the :rst:role:`py:func` role.
 
+   .. rst:directive:option:: single-line-parameter-list
+      :type: no value
+
+      Ensures that the decorator's arguments will be emitted on a single logical
+      line, overriding :confval:`python_maximum_signature_line_length` and
+      :confval:`maximum_signature_line_length`.
+
+      .. versionadded:: 7.1
+
 .. rst:directive:: .. py:decoratormethod:: name
                    .. py:decoratormethod:: name(signature)
 
@@ -763,6 +800,15 @@ The C domain (name **c**) is suited for documentation of C API.
       :retval NULL: under some conditions.
       :retval NULL: under some other conditions as well.
 
+   .. rst:directive:option:: single-line-parameter-list
+      :type: no value
+
+      Ensures that the function's parameters will be emitted on a single logical
+      line, overriding :confval:`c_maximum_signature_line_length` and
+      :confval:`maximum_signature_line_length`.
+
+      .. versionadded:: 7.1
+
 
 .. rst:directive:: .. c:macro:: name
                    .. c:macro:: name(arg list)
@@ -776,6 +822,15 @@ The C domain (name **c**) is suited for documentation of C API.
    .. versionadded:: 3.0
       The function style variant.
 
+   .. rst:directive:option:: single-line-parameter-list
+      :type: no value
+
+      Ensures that the macro's parameters will be emitted on a single logical
+      line, overriding :confval:`c_maximum_signature_line_length` and
+      :confval:`maximum_signature_line_length`.
+
+      .. versionadded:: 7.1
+
 .. rst:directive:: .. c:struct:: name
 
    Describes a C struct.
@@ -1126,6 +1181,15 @@ visibility statement (``public``, ``private`` or ``protected``).
       .. cpp:function:: template<> \
                         void print(int i)
 
+   .. rst:directive:option:: single-line-parameter-list
+      :type: no value
+
+      Ensures that the function's parameters will be emitted on a single logical
+      line, overriding :confval:`cpp_maximum_signature_line_length` and
+      :confval:`maximum_signature_line_length`.
+
+      .. versionadded:: 7.1
+
 .. rst:directive:: .. cpp:member:: (member) variable declaration
                    .. cpp:var:: (member) variable declaration
 
@@ -1908,13 +1972,31 @@ The JavaScript domain (name **js**) provides the following directives:
       :throws SomeError: For whatever reason in that case.
       :returns: Something.
 
+   .. rst:directive:option:: single-line-parameter-list
+      :type: no value
+
+      Ensures that the function's parameters will be emitted on a single logical
+      line, overriding :confval:`javascript_maximum_signature_line_length` and
+      :confval:`maximum_signature_line_length`.
+
+      .. versionadded:: 7.1
+
 .. rst:directive:: .. js:method:: name(signature)
 
    This directive is an alias for :rst:dir:`js:function`, however it describes
    a function that is implemented as a method on a class object.
 
    .. versionadded:: 1.6
 
+   .. rst:directive:option:: single-line-parameter-list
+      :type: no value
+
+      Ensures that the function's parameters will be emitted on a single logical
+      line, overriding :confval:`javascript_maximum_signature_line_length` and
+      :confval:`maximum_signature_line_length`.
+
+      .. versionadded:: 7.1
+
 .. rst:directive:: .. js:class:: name
 
    Describes a constructor that creates an object.  This is basically like a
@@ -1933,6 +2015,15 @@ The JavaScript domain (name **js**) provides the following directives:
       :param string name: The name of the animal
       :param number age: an optional age for the animal
 
+   .. rst:directive:option:: single-line-parameter-list
+      :type: no value
+
+      Ensures that the function's parameters will be emitted on a single logical
+      line, overriding :confval:`javascript_maximum_signature_line_length` and
+      :confval:`maximum_signature_line_length`.
+
+      .. versionadded:: 7.1
+
 .. rst:directive:: .. js:data:: name
 
    Describes a global variable or constant.

sphinx/addnodes.py

@@ -246,7 +246,12 @@ def astext(self) -> str:
 
 
 class desc_parameterlist(nodes.Part, nodes.Inline, nodes.FixedTextElement):
-    """Node for a general parameter list."""
+    """Node for a general parameter list.
+
+    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.
+    """
     child_text_separator = ', '
 
     def astext(self):

sphinx/config.py

@@ -137,7 +137,7 @@ class Config:
         'numfig': (False, 'env', []),
         'numfig_secnum_depth': (1, 'env', []),
         'numfig_format': ({}, 'env', []),  # will be initialized in init_numfig_format()
-
+        'maximum_signature_line_length': (None, 'env', {int, None}),
         'math_number_all': (False, 'env', []),
         'math_eqref_format': (None, 'env', [str]),
         'math_numfig': (True, 'env', []),

sphinx/domains/c.py

@@ -727,9 +727,19 @@ def _stringify(self, transform: StringifyTransform) -> str:
     def describe_signature(self, signode: TextElement, mode: str,
                            env: BuildEnvironment, symbol: Symbol) -> None:
         verify_description_mode(mode)
+        multi_line_parameter_list = False
+        test_node: Element = signode
+        while test_node.parent:
+            if not isinstance(test_node, addnodes.desc_signature):
+                test_node = test_node.parent
+                continue
+            multi_line_parameter_list = test_node.get('multi_line_parameter_list', False)
+            break
+
         # only use the desc_parameterlist for the outer list, not for inner lists
         if mode == 'lastIsName':
             paramlist = addnodes.desc_parameterlist()
+            paramlist['multi_line_parameter_list'] = multi_line_parameter_list
             for arg in self.args:
                 param = addnodes.desc_parameter('', '', noemph=True)
                 arg.describe_signature(param, 'param', env, symbol=symbol)
@@ -3153,6 +3163,7 @@ class CObject(ObjectDescription[ASTDeclaration]):
     option_spec: OptionSpec = {
         'noindexentry': directives.flag,
         'nocontentsentry': directives.flag,
+        'single-line-parameter-list': directives.flag,
     }
 
     def _add_enumerator_to_parent(self, ast: ASTDeclaration) -> None:
@@ -3258,6 +3269,14 @@ def run(self) -> list[Node]:
     def handle_signature(self, sig: str, signode: TextElement) -> ASTDeclaration:
         parentSymbol: Symbol = self.env.temp_data['c:parent_symbol']
 
+        max_len = (self.env.config.c_maximum_signature_line_length
+                   or self.env.config.maximum_signature_line_length
+                   or 0)
+        signode['multi_line_parameter_list'] = (
+            'single-line-parameter-list' not in self.options
+            and (len(sig) > max_len > 0)
+        )
+
         parser = DefinitionParser(sig, location=signode, config=self.env.config)
         try:
             ast = self.parse_definition(parser)
@@ -3866,11 +3885,12 @@ def setup(app: Sphinx) -> dict[str, Any]:
     app.add_config_value("c_id_attributes", [], 'env')
     app.add_config_value("c_paren_attributes", [], 'env')
     app.add_config_value("c_extra_keywords", _macroKeywords, 'env')
+    app.add_config_value("c_maximum_signature_line_length", None, 'env', types={int, None})
     app.add_post_transform(AliasTransform)
 
     return {
         'version': 'builtin',
-        'env_version': 2,
+        'env_version': 3,
         'parallel_read_safe': True,
         'parallel_write_safe': True,
     }