feat: add rollback/down migrations support

[roor0]

Summary

Adds automatic down migration generation and runtime rollback support to Drizzle.

Down SQL Generation (drizzle-kit)

• drizzle-kit generate now produces a down.sql file alongside each migration.sql
• Down SQL is generated by running the schema diff in reverse with rename-aware resolvers
• Renames produce proper RENAME statements instead of destructive DROP/CREATE
• Supported for all dialects: PostgreSQL, MySQL, SQLite, LibSQL, SingleStore, CockroachDB
• Bundled migrations (Expo, Durable SQLite, OP-SQLite) gain a downMigrations record in migrations.js

Runtime Rollback (drizzle-orm)

• New rollback(db, config, steps?) export on every driver migrator
• Reads the N most-recently-applied migrations from the tracking table
• Executes their down SQL in reverse order within a transaction
• Removes the corresponding tracking rows
• Supports all 30+ driver adapters

Files Changed

• drizzle-kit: generate-common.ts, generate-down-helpers.ts (new), all generate-*.ts files
• drizzle-orm: migrator.ts, all dialect dialect.ts files, all driver migrator.ts files
• Tests: down-sql.test.ts, down-helpers.test.ts

Test plan

• Unit tests for writeResult down SQL file generation
• Unit tests for embeddedMigrations down SQL bundling
• Unit tests for withCapture rename capture
• Unit tests for makeInverseResolver rename inversion
• TypeScript compilation passes (tsc --noEmit)
• Integration tests with actual database rollback (future)

[theholla]

I'm curious if this is still in the works? My team just started using drizzle and this rollback piece would def come in handy.

[alexbitar98]

please let's push this asap its very needed

[a-husic]

do we really need to put this all over reddit? Please prioritize

[AndriiSherman]

Thanks for you PR!

The question is, how would custom migrations be handled? How would it handle the cases, where someone changed generated sql file with some custom statements?

[roor0]

Good question — a couple of things worth calling out explicitly, and I've just pushed a follow-up commit addressing them:

1. drizzle-kit generate --custom — previously skipped down.sql entirely. It now emits an empty scaffold (-- Custom SQL rollback file, put your reverse statements below! --) alongside the placeholder migration.sql, so users have a clear home for the inverse statements.

2. Hand-edited generated migrations — the auto-generated down.sql is produced from the reverse schema diff and is intended as a starting point. It's now prefixed with a header explicitly stating it's editable and should be kept in sync with migration.sql when the developer adds custom SQL. This matches the Rails / Flyway / TypeORM convention: the tool seeds a reasonable default, the developer owns the file.

3. Opt-out — a new generateDownMigrations config flag (default true) is available for teams who'd rather manage rollback SQL entirely by hand. Setting it to false skips both the reverse diff and the down.sql emission.

Happy to iterate further if you'd like a different contract here.