pair_changed_together

If the <since>...HEAD diff changes any path matching if_changed:, at least one path matching then_changed: must change in the same range — the co-change gate. Corpus signals: rust’s rustdoc-json-types FORMAT_VERSION must bump when the format struct changes; “version.txt and the lockfile change together” release guards. Both globs and since: (the base ref) are required. Directional — the trigger is if_changed, the obligation is then_changed; a then_changed-only change never fires it, so add a second rule with the globs swapped for a bidirectional pact. The changeset_requires_path sibling, built on the same merge-base diff as alint check --changed. Silent no-op outside a git repo or when if_changed didn’t change; a since: that fails to resolve hard-fails with a shallow-clone hint.

- id: format-version-bumped
  kind: pair_changed_together
  if_changed: "src/rustdoc-json-types/lib.rs"     # if the format struct changes…
  then_changed: "src/rustdoc-json-types/FORMAT_VERSION"  # …the version file must too
  since: "{{env.ALINT_BASE_SHA | default('origin/main')}}"
  level: error

---

Options

Option	Type	Required	Default	Description
if_changed	string	yes		Glob; the trigger. When the diff changes a path matching this, a then_changed co-change is required.
since	string	yes		Base ref for the <since>...HEAD diff. Use the canonical {{env.X}} interpolation, e.g. since: "{{env.ALINT_BASE_SHA | default('origin/main')}}".
then_changed	string	yes		Glob; the obligation. At least one changed path must match it whenever if_changed fired.

Plus the common level, id, and when fields. This rule analyses the whole repository, so it takes no paths. This table is generated from the JSON Schema; option types and defaults are authoritative.