🐛 fix: give untitled argument groups a heading

An argument group created with only a description rendered its heading
as the program name followed by nothing, because the title was None,
and every such group shared the label tool-None; two of them raised a
duplicate label warning that fails builds run with -W.

The description now serves as the heading when the title is missing,
and a group with neither falls back to "arguments", so each section
keeps a distinct, stable anchor. Titled groups are untouched.

Author: gaborbernat

CHANGELOG.md

@@ -13,6 +13,8 @@ All notable changes to this project will be documented in this file.
   literals.
 - Make `:hook:` intercept `parse_intermixed_args()` as well as `parse_args()`.
 - Keep ANSI color codes out of usage blocks when `PYTHON_COLORS=1` is set on Python 3.14 or newer.
+- Use the description, or `arguments`, as the heading of an argument group without a title instead of rendering `None`
+  and emitting duplicate label warnings.
 
 ## 1.13.1
 

roots/test-group-untitled/conf.py

@@ -0,0 +1,8 @@
+from __future__ import annotations
+
+import sys
+from pathlib import Path
+
+sys.path.insert(0, str(Path(__file__).parent))
+extensions = ["sphinx_argparse_cli"]
+nitpicky = True

roots/test-group-untitled/index.rst

@@ -0,0 +1,3 @@
+.. sphinx_argparse_cli::
+  :module: parser
+  :func: make

roots/test-group-untitled/parser.py

@@ -0,0 +1,11 @@
+from __future__ import annotations
+
+from argparse import ArgumentParser
+
+
+def make() -> ArgumentParser:
+    parser = ArgumentParser(prog="tool")
+    parser.add_argument_group(description="only a description").add_argument("--x", help="x help")
+    parser.add_argument_group(description="another").add_argument("--y", help="y help")
+    parser.add_argument_group().add_argument("--z", help="z help")
+    return parser

src/sphinx_argparse_cli/_logic.py

@@ -209,13 +209,15 @@ def _pre_format(self, block: str | None) -> paragraph | literal_block | None:
     def _mk_option_group(self, group: _ArgumentGroup, prefix: str, prog: str) -> section:
         sub_title_prefix: str = self.options.get("group_sub_title_prefix")
         title_prefix = self.options.get("group_title_prefix")
-        title_text = self._build_opt_grp_title(group, prefix, prog, sub_title_prefix, title_prefix)
-        title_ref: str = f"{prefix}{' ' if prefix else ''}{group.title}"
+        # an untitled group borrows its description as heading so its anchor stays unique
+        group_title = group.title or group.description or "arguments"
+        title_text = self._build_opt_grp_title(group_title, prefix, prog, sub_title_prefix, title_prefix)
+        title_ref: str = f"{prefix}{' ' if prefix else ''}{group_title}"
         ref_id = self._make_id(title_ref)
         # the text sadly needs to be prefixed, because otherwise the autosectionlabel will conflict
         header = title("", Text(title_text))
         group_section = section("", header, ids=[ref_id], names=[ref_id])
-        if description := self._pre_format(group.description):
+        if group.title and (description := self._pre_format(group.description)):
             group_section += description
         self._register_ref(ref_id, title_text, group_section)
         opt_group = bullet_list()
@@ -228,12 +230,10 @@ def _mk_option_group(self, group: _ArgumentGroup, prefix: str, prog: str) -> sec
         return group_section
 
     def _build_opt_grp_title(
-        self, group: _ArgumentGroup, prefix: str, prog: str, sub_title_prefix: str, title_prefix: str
+        self, group_title: str, prefix: str, prog: str, sub_title_prefix: str, title_prefix: str
     ) -> str:
         sub_cmd = prefix[len(prog) :].strip() or None if prefix != prog else None
-        title_text = self._resolve_prefix(prog, sub_cmd, prefix, title_prefix, sub_title_prefix)
-        title_text += group.title or ""
-        return title_text
+        return self._resolve_prefix(prog, sub_cmd, prefix, title_prefix, sub_title_prefix) + group_title
 
     def _mk_option_line(self, action: Action, prefix: str) -> list_item:
         line = paragraph()

tests/test_logic.py

@@ -303,6 +303,19 @@ def test_usage_ignores_python_colors(build_outcome: str) -> None:
     )
 
 
+@pytest.mark.sphinx(buildername="html", testroot="group-untitled")
+def test_group_untitled(build_outcome: str, warning: StringIO) -> None:
+    headings = re.findall(r'<h2>(.*?)<a class="headerlink" href="(#[^"]+)"', build_outcome)
+    assert headings == [
+        ("tool options", "#tool-options"),
+        ("tool only a description", "#tool-only-a-description"),
+        ("tool another", "#tool-another"),
+        ("tool arguments", "#tool-arguments"),
+    ]
+    assert "<p>only a description</p>" not in build_outcome
+    assert not warning.getvalue()
+
+
 @pytest.mark.sphinx(buildername="text", testroot="ref-duplicate-label")
 def test_ref_duplicate_label(build_outcome: tuple[str, str], warning: StringIO) -> None:
     assert build_outcome