feat: add K8SCharmConfig for the K8s-only locales (#150)

* feat: add K8s locale superset to single kernel

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>

* feat: add K8SCharmConfig for the K8s-only locales

#137's CharmConfig validates response-lc-* against SNAP_LOCALES, the VM
snap's locale set. The K8s rock additionally ships C.utf8 and POSIX, so
the K8s charm must accept them. Add K8SCharmConfig, a CharmConfig
subclass that widens the three locale fields to K8S_LOCALES, so each
substrate validates against the locales actually available to it.

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

* build: bump library version to 16.3.0

The aux migration adds new public API to the library (K8SCharmConfig,
K8S_LOCALES, the shared constants and the architecture guard), so raise
the minor version for the next release. Aligns with the 16.3.0 target of
the cluster work in #145.

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

* build: make psycopg2 an optional extra

psycopg2 is only needed by the library's PostgreSQL client code, but as
a top-level dependency it forced every consumer — including the charms'
integration tests, which import only the pure-Python locale constants —
to build it from source. Move it into the `postgresql` extra so a bare
install skips it; consumers using the DB code request `[postgresql]`.

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

---------

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

Author: marceloneppel

pyproject.toml

@@ -4,7 +4,7 @@
 [project]
 name = "postgresql-charms-single-kernel"
 description = "Shared and reusable code for PostgreSQL-related charms"
-version = "16.2.2"
+version = "16.3.0"
 readme = "README.md"
 license = {file = "LICENSE"}
 authors = [
@@ -18,12 +18,12 @@ classifiers = [
 requires-python = ">=3.8,<4.0"
 dependencies = [
     "ops>=2.0.0",
-    "psycopg2>=2.9.10",
     "tenacity>=9.0.0",
 ]
 
 [project.optional-dependencies]
 postgresql = [
+    "psycopg2>=2.9.10",
     "httpx; python_version >= '3.12'",
     "data-platform-helpers>=0.1.7; python_version >= '3.12'",
     "charmlibs-pathops>=1.0.1; python_version >= '3.12'",

single_kernel_postgresql/core/config.py

@@ -9,7 +9,7 @@
 
 from pydantic import Field, NonNegativeInt, PositiveInt
 
-from single_kernel_postgresql.config.locales import SNAP_LOCALES
+from single_kernel_postgresql.config.locales import K8S_LOCALES, SNAP_LOCALES
 from single_kernel_postgresql.lib.charms.data_platform_libs.v1.data_models import BaseConfigModel
 
 logger = logging.getLogger(__name__)
@@ -252,3 +252,15 @@ def keys(cls) -> list[str]:
     def plugin_keys(cls) -> filter:
         """Return plugin config names in a iterable."""
         return filter(lambda x: x.startswith("plugin_"), cls.keys())
+
+
+class K8SCharmConfig(CharmConfig):
+    """Structured configuration for the K8s charm.
+
+    Identical to :class:`CharmConfig`, but the locale options also accept the two
+    locales the K8s rock provides and the VM snap does not (``C.utf8``, ``POSIX``).
+    """
+
+    response_lc_monetary: K8S_LOCALES | None = Field(default=None)
+    response_lc_numeric: K8S_LOCALES | None = Field(default=None)
+    response_lc_time: K8S_LOCALES | None = Field(default=None)

tests/unit/test_config.py

@@ -0,0 +1,44 @@
+# Copyright 2026 Canonical Ltd.
+# See LICENSE file for licensing details.
+from typing import get_args
+
+import pytest
+from pydantic import TypeAdapter, ValidationError
+from single_kernel_postgresql.core.config import CharmConfig, K8SCharmConfig
+
+_LOCALE_FIELDS = ("response_lc_monetary", "response_lc_numeric", "response_lc_time")
+
+
+def _locale_values(model: type, field: str) -> set[str]:
+    annotation = model.model_fields[field].annotation
+    literal = next(arm for arm in get_args(annotation) if arm is not type(None))
+    return set(get_args(literal))
+
+
+def test_charmconfig_imports_and_keys_resolve():
+    keys = CharmConfig.keys()
+    for field in _LOCALE_FIELDS:
+        assert field in keys
+
+
+def test_k8s_config_adds_exactly_the_rock_only_locales():
+    """K8s locale fields are the shared set plus exactly C.utf8 and POSIX."""
+    for field in _LOCALE_FIELDS:
+        base = _locale_values(CharmConfig, field)
+        k8s = _locale_values(K8SCharmConfig, field)
+        assert "C" in base and "C.utf8" not in base and "POSIX" not in base
+        assert k8s - base == {"C.utf8", "POSIX"}
+        assert base - k8s == set()
+
+
+def test_locale_fields_validate_per_substrate():
+    """The VM model rejects C.utf8/POSIX; the K8s model accepts them."""
+    for field in _LOCALE_FIELDS:
+        base = TypeAdapter(CharmConfig.model_fields[field].annotation)
+        k8s = TypeAdapter(K8SCharmConfig.model_fields[field].annotation)
+        for locale in ("C.utf8", "POSIX"):
+            with pytest.raises(ValidationError):
+                base.validate_python(locale)
+            k8s.validate_python(locale)
+        base.validate_python("C")
+        k8s.validate_python("C")