FIX: set intermediate TOML tables to be super table (#368)

* DX: add `create_sub_table()` test for super tables

src/compwa_policy/utilities/pyproject/setters.py

@@ -67,9 +67,11 @@ def _sort_taplo(items: Iterable[str]) -> list[str]:
 def create_sub_table(config: Mapping[str, Any], dotted_header: str) -> Table:
     """Create a TOML sub-table through a dotted header key."""
     current_table: Any = config
-    for header in dotted_header.split("."):
+    header_hierarchy = dotted_header.split(".")
+    for i, header in enumerate(header_hierarchy, 1):
         if header not in current_table:
-            current_table[header] = tomlkit.table()
+            is_last_header = i == len(header_hierarchy)
+            current_table[header] = tomlkit.table(is_super_table=not is_last_header)
         current_table = current_table[header]
     return current_table
 

tests/utilities/pyproject/test_setters.py

@@ -155,3 +155,23 @@ def test_create_sub_table(table_key: str):
         lint = ["ruff"]
     """)
     assert new_content.strip() == expected.strip()
+
+
+def test_create_sub_table_with_super_table():
+    pyproject = load_pyproject_toml("", modifiable=True)
+    pixi = create_sub_table(pyproject, "tool.pixi")
+    pixi["channels"] = ["conda-forge"]
+    pixi["platforms"] = ["linux-64"]
+    task_table = create_sub_table(pyproject, "tool.pixi.feature.dev.tasks.test")
+    task_table["cmd"] = "pytest"
+
+    new_content = tomlkit.dumps(pyproject)
+    expected = dedent("""
+        [tool.pixi]
+        channels = ["conda-forge"]
+        platforms = ["linux-64"]
+
+        [tool.pixi.feature.dev.tasks.test]
+        cmd = "pytest"
+    """)
+    assert new_content.strip() == expected.strip()