Register the factor label for a bare labeled dict in env_list

The configuration reference states that a bare labeled dict in env_list
'also registers a {factor:label} name', but _extract_env_list_labels only
walked items carrying a 'product' key, so {factor:ecosystem} resolved to
an empty string for the bare form while the product-wrapped form resolved
it correctly.

Author: dylanpulver

docs/changelog/4062.bugfix.rst

@@ -0,0 +1,2 @@
+Register the ``{factor:label}`` name for a bare labeled dict in ``env_list``, as the configuration reference documents;
+previously only a labeled group nested inside a ``product`` dict registered one - by :user:`dylanpulver`.

src/tox/config/source/toml_pyproject.py

@@ -219,7 +219,9 @@ def _extract_env_list_labels(env_list_raw: TomlTypes) -> dict[str, FactorGroup]:
         return {}
     labels: dict[str, FactorGroup] = {}
     for item in env_list_raw:
-        if isinstance(item, dict) and "product" in item:
+        if not isinstance(item, dict):
+            continue
+        if "product" in item:
             raw_groups = item["product"]
             if not isinstance(raw_groups, list):
                 continue
@@ -229,6 +231,9 @@ def _extract_env_list_labels(env_list_raw: TomlTypes) -> dict[str, FactorGroup]:
                 labels[str(idx)] = group
                 if (label := extract_label(g)) is not None:
                     labels[label] = group
+        elif (label := extract_label(item)) is not None:  # a bare labeled dict is its own single factor group
+            values = expand_factor_group(item)
+            labels[label] = FactorGroup(values=values, default=extract_default(item, values))
     return labels
 
 

tests/config/source/test_toml_tox.py

@@ -116,6 +116,46 @@ def test_config_in_toml_replace_from_section_absolute(tox_project: ToxProjectCre
     outcome.assert_out_err("[testenv:B]\ndescription = o\n", "")
 
 
+def test_config_in_toml_env_list_bare_labeled_factor_description(tox_project: ToxProjectCreator) -> None:
+    project = tox_project({
+        "tox.toml": textwrap.dedent("""\
+            env_list = [
+                { ecosystem = ["oci", "python"] },
+            ]
+
+            [env_run_base]
+            package = "skip"
+            description = "Sync {factor:ecosystem} artifacts"
+            commands = [["python", "-c", "print('ok')"]]
+        """),
+    })
+    outcome = project.run("c", "-e", "oci", "-k", "description")
+    outcome.assert_success()
+    outcome.assert_out_err("[testenv:oci]\ndescription = Sync oci artifacts\n", "")
+    outcome = project.run("c", "-e", "python", "-k", "description")
+    outcome.assert_success()
+    outcome.assert_out_err("[testenv:python]\ndescription = Sync python artifacts\n", "")
+
+
+def test_config_in_toml_env_list_bare_labeled_factor_default(tox_project: ToxProjectCreator) -> None:
+    project = tox_project({
+        "tox.toml": textwrap.dedent("""\
+            env_list = [
+                { ecosystem = { values = ["oci", "python"], default = "oci" } },
+            ]
+
+            [env_run_base]
+            package = "skip"
+
+            [env.lint]
+            description = "Lint {factor:ecosystem} artifacts"
+        """),
+    })
+    outcome = project.run("c", "-e", "lint", "-k", "description")
+    outcome.assert_success()
+    outcome.assert_out_err("[testenv:lint]\ndescription = Lint oci artifacts\n", "")
+
+
 def test_config_in_toml_env_list_keyed_factor_description(tox_project: ToxProjectCreator) -> None:
     project = tox_project({
         "tox.toml": textwrap.dedent("""\