block migration-immutability
Once a migration has been applied in any environment, its content is
effectively frozen. golang-migrate sees "already at version N" and skips
re-running, so an in-place edit produces silent schema drift between
databases that ran the old version and those that ran the new one.
When this skill applies
The user is editing a migration file whose creation commit is reachable
from origin/main (i.e. the migration has already merged). Check via:
commit=$(git log --diff-filter=A --format=%H -- <path> | tail -1)
git merge-base --is-ancestor "$commit" origin/main && echo deployed
Falls back to main if origin/main isn't fetched. Don't use plain
git log -- <path> to make this decision — that scans the current
branch's history, not main's specifically, so a feature-branch migration
would be misclassified as deployed.
When this skill does NOT apply
- The user is creating a new migration. New migrations are how schema changes are supposed to land.
- The user is iterating on a migration inside an unmerged feature branch. Per project convention for net-new branch work, rebasing edits into the original migration is fine; immutability only kicks in after merge.
What to do
- Surface the immutability rule before the edit.
- Propose creating a new migration with
cd server && just db-migration-new <name>for the corrective change. Write both up and down migrations. - Run
just genafterward if any sqlc queries reference the changed schema.
What to avoid
- Do not edit deployed migrations in place to "fix" a bug — fix is a new migration.
- Do not delete or renumber existing migrations.