Rollback Rails migrations even when the migration file is missing.

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The Problem

When working with Rails migrations across git branches:

1. You run migrations on a feature branch
2. Switch back to main
3. Run db:migrate - Rails dumps schema including changes from the other branch
4. You can't rollback because the migration files don't exist in current branch

Usual workaround: Switch to the other branch, rollback, switch back. Tedious.

The Solution

Mighost automatically captures migration file contents when they run, enabling rollback even when the original file is not present. It uses a 3-tier recovery strategy:

1. Stored snapshots — captured at migration time into a local SQLite file
2. Git history — searches across all branches
3. Worktree recovery — finds files in other git worktrees

Installation

Add to your Gemfile:

gem 'mighost', group: [:development, :test]

Then run:

bundle install
rails generate mighost:install

Add .mighost.sqlite3 to your .gitignore.

Requires Ruby >= 3.1 and Rails 6.1–8.1.

Usage

Check for orphaned migrations

rails mighost:status

Rollback orphaned migrations

# Interactive (with confirmation)
rails mighost:rollback

# Force (no confirmation)
FORCE=1 rails mighost:rollback

# Specific version
rails mighost:rollback VERSION=20240115123456

Scan existing migrations & git history

If you install Mighost on an existing project:

rails mighost:scan

All commands

Command	Description	Options
mighost:status	Show orphaned migrations	DEBUG=1, SHOW_DISMISSED=1
mighost:rollback	Rollback orphaned migrations	VERSION=x, FORCE=1
mighost:scan	Capture migrations + search git	RESCAN=1
mighost:list (ls)	List stored migration records	LIMIT=N
mighost:dismiss	Hide migrations from status	VERSION=x, VERSION=a..b, OLD=1
mighost:undismiss	Restore dismissed migrations	VERSION=x
mighost:dismissed	List dismissed migrations
mighost:cleanup	Remove stale records	FORCE=1
mighost:help	Show command reference

Version ranges

VERSION=20240115123456       # Single version
VERSION=20240110..20240120   # Inclusive range
VERSION=20240110..           # From version onwards
VERSION=..20240120           # Up to version

Configuration

# config/initializers/mighost.rb
Mighost.configure do |config|
  # Path to SQLite file (relative to Rails.root)
  config.storage_path = ".mighost.sqlite3"

  # Auto-capture on migrate
  config.auto_capture = true

  # Store git metadata
  config.store_git_metadata = true

  # Enable/disable (disabled in production by default)
  config.enabled = !Rails.env.production?
end

Rich Output with Railbow

By default, Mighost outputs plain, uncolored text. For rich, colorized output with tables, emojis, and git enrichment, use the railbow gem:

gem 'railbow'

Railbow automatically detects Mighost and enhances its output.

Public API

Mighost exposes a stable API for programmatic access:

# Detect orphaned migrations
Mighost::API.orphaned_migrations                  # => [OrphanedMigration, ...]

# Find snapshots
Mighost::API.find_snapshot("20240115123456")       # => Snapshot or nil
Mighost::API.find_or_recover_snapshot("20240115")  # => Snapshot (with git/worktree fallback)

# Scan and recover
Mighost::API.scan!(rescan: false)                  # => {captured:, git_recovered:, ...}

# Rollback
Mighost::API.rollback_version!("20240115123456")   # raises on failure

UI Adapter

Mighost uses a pluggable UI adapter for output. Replace it to customize formatting:

# In your railtie or initializer:
Mighost.ui = YourCustomUI.new

The adapter must implement: render_orphans, render_records, render_recoverable_list, render_scan_details, render_scan_results, render_dismiss_preview, render_dismiss_remaining, render_dismissed_list, confirm?, confirm_each?, confirm_dismiss?, success, error, warning, info, hint. See Mighost::PlainUI for the reference implementation.

How It Works

1. Capture: When you run db:migrate, Mighost hooks into ActiveRecord::Migrator and stores the migration file content along with git metadata (branch, SHA) in a local SQLite file.

2. Detect: mighost:status compares schema_migrations table with actual migration files to find orphans.

3. Recover: For missing files, Mighost searches stored snapshots, git history (all branches), and other git worktrees.

4. Rollback: Writes recovered content to a temp file, loads it, calls the down method, then removes the version from schema_migrations.

Limitations

• Irreversible migrations: If the migration raises ActiveRecord::IrreversibleMigration, Mighost can't help.
• Model dependencies: If your migration references models/classes that don't exist in the current branch, the rollback may fail.
• Manual SQL changes: If someone manually modified the database, rollback might not work correctly.
• Trust: Recovered migration code (from snapshots, git history, or worktrees) is executed with the same trust as your own migrations — it is code from your repository, run by you.

Contributing

Bug reports and pull requests are welcome on GitHub. Run bundle exec rake (specs + standardrb) before submitting.

License

MIT License. See LICENSE.