feat: add K8s locale superset to single kernel (#149)

The K8s rock ships C.utf8 and POSIX (from the base image's libc-bin)
that the VM snap's locales-all omits, so #137's single SNAP_LOCALES
rejects those otherwise-valid values for the K8s response-lc-* config.
Add K8S_LOCALES extending SNAP_LOCALES with the two rock-only entries so
the K8s config model can accept them while VM keeps the snap-only set.

Signed-off-by: Marcelo Henrique Neppel <marcelo.neppel@canonical.com>

Author: marceloneppel

single_kernel_postgresql/config/locales.py

@@ -1,7 +1,12 @@
 # Copyright 2024 Canonical Ltd.
 # See LICENSE file for licensing details.
 
-"""List of locales available in the snap."""
+"""Locales accepted by the PostgreSQL ``response_lc_*`` config options.
+
+``SNAP_LOCALES`` is the set the VM snap ships (it stages ``locales-all``). The
+K8s rock additionally ships ``C.utf8`` and ``POSIX`` (from the Ubuntu base's
+``libc-bin``), so ``K8S_LOCALES`` extends ``SNAP_LOCALES`` with those two.
+"""
 
 from typing import Literal
 
@@ -516,3 +521,7 @@
     "zu_ZA",
     "zu_ZA.utf8",
 ]
+
+
+# The K8s rock additionally ships these (from libc-bin); the VM snap does not.
+K8S_LOCALES = Literal[SNAP_LOCALES, "C.utf8", "POSIX"]

tests/unit/test_locales.py

@@ -0,0 +1,19 @@
+# Copyright 2026 Canonical Ltd.
+# See LICENSE file for licensing details.
+from typing import get_args
+
+from single_kernel_postgresql.config.locales import K8S_LOCALES, SNAP_LOCALES
+
+
+def test_snap_locales_exclude_k8s_only_entries():
+    members = get_args(SNAP_LOCALES)
+    assert "C" in members
+    assert "C.utf8" not in members
+    assert "POSIX" not in members
+
+
+def test_k8s_locales_extend_snap_with_rock_only_entries():
+    snap = set(get_args(SNAP_LOCALES))
+    k8s = set(get_args(K8S_LOCALES))
+    assert k8s - snap == {"C.utf8", "POSIX"}
+    assert snap - k8s == set()