hier_config: Skill for Claude Code

Build a New hier_config Platform Driver

Scaffold an in-tree platform driver the way this repo expects. The authoritative recipe is docs/dev/extending.md; this skill adds the concrete templates. For a driver that lives outside this repo (in user code), follow docs/user/custom-drivers.md#creating-a-custom-driver instead.

Step 1: Characterize the Platform

Answer these before writing code — they determine which overrides and rules the driver needs. Study real config samples from the platform:

Question	Driver hook if non-default
Negation prefix (no ? undo ? delete ?)	negation_prefix property (default "no ")
Some commands reset with a different form?	NegationDefaultWithRule / override swap_negation
Sections closed with an exit token (exit, quit, end-*)?	SectionalExitingRule / override sectional_exit
Last-write-wins commands (hostname, description, …)?	IdempotentCommandsRule
Comment/banner lines to strip on load?	PerLineSubRule / FullTextSubRule
Blocks with irregular indentation?	IndentAdjustRule
Flat set/delete syntax (Junos-like)?	config_preprocessor + declaration_prefix (see platforms/vyos/driver.py)
Order-sensitive commands?	OrderingRule with weights

Reference implementations: platforms/huawei_vrp/driver.py (small, rule-based), platforms/vyos/driver.py (preprocessor-based), platforms/cisco_ios/driver.py (comprehensive).

Step 2: Write the Failing Test First (TDD)

Create tests/test_driver_<platform>.py before the driver exists — conventions in docs/dev/testing.md. Flat functions, full annotations, round-trip idiom:

from hier_config import Platform, get_hconfig_fast_load


def test_negation_prefix() -> None:
    running_config = get_hconfig_fast_load(
        Platform.ACME_OS, ("interface eth0", "  shutdown")
    )
    generated_config = get_hconfig_fast_load(
        Platform.ACME_OS, ("interface eth0",)
    )
    remediation = running_config.config_to_get_to(generated_config)
    assert remediation.dump_simple() == ("interface eth0", "  no shutdown")

    running_after = running_config.future(remediation)
    rollback = running_after.config_to_get_to(running_config)
    running_after_rollback = running_after.future(rollback)
    assert not tuple(running_config.unified_diff(running_after_rollback))