Changes to consider for next major release (4.x)

[benhoyt]

Please add to this list as we go:

• Remove the "compatibility imports" from ops.testing, ops.model, etc (for example see ci: check httpbin-demo example charm with mypy #2339)
• Things that have a deprecation warning/docstring (see comment below)
• Drop Python 3.10
• Drop Juju 2.9 / Juju < 3.6
• perf!: testing yaml optimisations #2361
• SCENARIO_BARE_CHARM_ERRORS default
• Bump min TLS to 1.3 in tracing
  • We'd want logs sinks to use Mozilla's generator
  • Case in point: Enhance the TLS cipher suite to exclude CBC traefik-k8s-operator#535
• Use TLS VERIFY_STRICT in tracing matrix message
• ops.Relation.load() should perhaps be strict #2333

[dimaqq]

Deprecations to consider

• ops.main.main(...) legacy entrypoint is deprecated in favour of ops.main() (ops/main.py).
• Legacy ops.main import path is maintained for compatibility and re-exports internal symbols from ops._main (legacy/deprecated path context) (ops/main.py).
• Entire ops.lib functionality is deprecated (ops/lib/__init__.py).
• ops.lib.use(...) is deprecated (ops/lib/__init__.py).
• ops.lib.autoimport() is deprecated (ops/lib/__init__.py).
• Model.pod property is deprecated (sidecar + Pebble recommended) (ops/model.py).
• Pod class is deprecated (ops/model.py).
• OpenedPort alias is deprecated; use Port (ops/model.py).
• Storage.id attribute/property is deprecated; use Storage.index (ops/model.py).
• StatusBase.register(...) is deprecated/internal-only (ops/model.py).
• Omitting model_uuid in SecretInfo(...) is deprecated and will become required (ops/model.py).
• JujuVersion.from_environ() is deprecated; use Model.juju_version (ops/jujuversion.py).
• LeaderSettingsChangedEvent / leader_settings_changed event is deprecated (use peer relation app databag) (ops/charm.py, ops/charm.py).
• PreSeriesUpgradeEvent and PostSeriesUpgradeEvent are on deprecated/removed-by-Juju path (jujuremoved:: 4.0, runtime deprecation warnings) (ops/charm.py).
• CollectMetricsEvent is on deprecated/removed-by-Juju path (jujuremoved:: 3.6.11, runtime deprecation warning) (ops/charm.py).
• Legacy hooks execution path is deprecated (ops/_main.py).
• Controller storage usage (use_juju_for_storage=True) is deprecated (ops/_main.py).
• Framework.__init__ old signatures are deprecated/legacy-supported: storage as path string and charm_dir=None (ops/framework.py).
• ops.testing.Harness is deprecated (pending deprecation warning + docs) (ops/_private/harness.py, ops/testing.py, docs/reference/ops-testing-harness.rst).
• Scenario API: Context.charm_spec property is deprecated (testing/src/scenario/context.py).
• Scenario API: Address.address is a deprecated alias for Address.value (testing/src/scenario/state.py).
• Scenario historical args: pre_event / post_event arguments to run/run_action are documented as deprecated/removed (testing/UPGRADING.md).