Add option_emphasise_placeholders config value.

Support parsing of "variable part" for option directives similarly
to samp roles.

Fixes: #9965.

Co-authored-by: Adam Turner <9087854+AA-Turner@users.noreply.github.com>
Signed-off-by: Martin Liska <mliska@suse.cz>

doc/usage/configuration.rst

@@ -706,6 +706,15 @@ General configuration
 
     .. versionadded:: 3.0
 
+.. confval:: option_emphasise_placeholders
+
+   Default is ``False``.
+   When enabled, emphasise placeholders in ``.. option:`` directives.
+   To display literal braces, escape with a backslash (``\{``). For example,
+   ``option_emphasise_placeholders=True`` and ``.. option:: -foption={TYPE}`` would
+   render with ``TYPE`` emphasised.
+
+   .. versionadded:: 5.1
 
 .. _intl-options:
 

doc/usage/restructuredtext/domains.rst

@@ -1750,6 +1750,9 @@ There is a set of directives allowing documenting command-line programs:
    referenceable by :rst:role:`option` (in the example case, you'd use something
    like ``:option:`dest_dir```, ``:option:`-m```, or ``:option:`--module```).
 
+   Use :confval:`option_emphasise_placeholders` for parsing of
+   "variable part" of a literal text (similarly to the ``samp`` role).
+
    ``cmdoption`` directive is a deprecated alias for the ``option`` directive.
 
 .. rst:directive:: .. envvar:: name

sphinx/config.py

@@ -140,6 +140,7 @@ class Config:
         'smartquotes_excludes': ({'languages': ['ja'],
                                   'builders': ['man', 'text']},
                                  'env', []),
+        'option_emphasise_placeholders': (False, 'env', []),
     }
 
     def __init__(self, config: Dict[str, Any] = {}, overrides: Dict[str, Any] = {}) -> None:

sphinx/domains/std.py

@@ -15,7 +15,7 @@
 from sphinx.directives import ObjectDescription
 from sphinx.domains import Domain, ObjType
 from sphinx.locale import _, __
-from sphinx.roles import XRefRole
+from sphinx.roles import EmphasizedLiteral, XRefRole
 from sphinx.util import docname_join, logging, ws_re
 from sphinx.util.docutils import SphinxDirective
 from sphinx.util.nodes import clean_astext, make_id, make_refnode
@@ -34,6 +34,8 @@
 # RE for grammar tokens
 token_re = re.compile(r'`((~?\w*:)?\w+)`', re.U)
 
+samp_role = EmphasizedLiteral()
+
 
 class GenericObject(ObjectDescription[str]):
     """
@@ -170,15 +172,41 @@ def handle_signature(self, sig: str, signode: desc_signature) -> str:
                                location=signode)
                 continue
             optname, args = m.groups()
-            if optname.endswith('[') and args.endswith(']'):
+            if optname[-1] == '[' and args[-1] == ']':
                 # optional value surrounded by brackets (ex. foo[=bar])
                 optname = optname[:-1]
                 args = '[' + args
 
             if count:
-                signode += addnodes.desc_addname(', ', ', ')
+                if self.env.config.option_emphasise_placeholders:
+                    signode += addnodes.desc_sig_punctuation(',', ',')
+                    signode += addnodes.desc_sig_space()
+                else:
+                    signode += addnodes.desc_addname(', ', ', ')
             signode += addnodes.desc_name(optname, optname)
-            signode += addnodes.desc_addname(args, args)
+            if self.env.config.option_emphasise_placeholders:
+                add_end_bracket = False
+                if not args:
+                    continue
+                if args[0] == '[' and args[-1] == ']':
+                    add_end_bracket = True
+                    signode += addnodes.desc_sig_punctuation('[', '[')
+                    args = args[1:-1]
+                if args[0] == ' ':
+                    signode += addnodes.desc_sig_space()
+                    args = args.strip()
+                if args[0] == '=':
+                    signode += addnodes.desc_sig_punctuation('=', '=')
+                    args = args[1:]
+                for part in samp_role.parse(args):
+                    if isinstance(part, nodes.Text):
+                        signode += nodes.Text(part.astext())
+                    else:
+                        signode += part
+                if add_end_bracket:
+                    signode += addnodes.desc_sig_punctuation(']', ']')
+            else:
+                signode += addnodes.desc_addname(args, args)
             if not count:
                 firstname = optname
                 signode['allnames'] = [optname]

tests/roots/test-root/objects.txt

@@ -194,6 +194,15 @@ Link to :option:`perl +p`, :option:`--ObjC++`, :option:`--plugin.option`, :optio
 
 Link to :option:`hg commit` and :option:`git commit -p`.
 
+.. option:: --abi={TYPE}
+
+.. option:: --test={WHERE}-{COUNT}
+
+.. option:: --wrap=\{\{value\}\}
+
+.. option:: -allowable_client {client_name}
+
+Foo bar.
 
 User markup
 ===========

tests/test_build_html.py

@@ -1735,3 +1735,25 @@ def test_html_code_role(app):
     assert ('<div class="highlight-python notranslate">' +
             '<div class="highlight"><pre><span></span>' +
             common_content) in content
+
+
+@pytest.mark.sphinx('html', testroot='root',
+                    confoverrides={'option_emphasise_placeholders': True})
+def test_option_emphasise_placeholders(app, status, warning):
+    app.build()
+    content = (app.outdir / 'objects.html').read_text()
+    assert '<em><span class="pre">TYPE</span></em>' in content
+    assert '{TYPE}' not in content
+    assert ('<em><span class="pre">WHERE</span></em>'
+            '<span class="pre">-</span>'
+            '<em><span class="pre">COUNT</span></em>' in content)
+    assert '<span class="pre">{{value}}</span>' in content
+
+
+@pytest.mark.sphinx('html', testroot='root')
+def test_option_emphasise_placeholders_default(app, status, warning):
+    app.build()
+    content = (app.outdir / 'objects.html').read_text()
+    assert '<span class="pre">={TYPE}</span>' in content
+    assert '<span class="pre">={WHERE}-{COUNT}</span></span>' in content
+    assert '<span class="pre">{client_name}</span>' in content