Test migrations reverse cleanly

.github/workflows/test.yml

@@ -135,6 +135,8 @@ jobs:
       - run: chrome --version
       - name: Checkout code
         uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
       - name: Update .ruby-version with matrix value
         run: echo "${{ matrix.ruby }}" >| .ruby-version
       # Dependencies
@@ -181,6 +183,10 @@ jobs:
                                       --format PreDocumentationFormatter \
                                       spec/generators
 
+      - name: Check generated migrations reverse cleanly
+        run: |
+          script/check_migrations.sh
+
       # Archive
       - name: Archive system spec screenshots
         uses: actions/upload-artifact@v3

demo/config/database.yml

@@ -18,6 +18,7 @@ default: &default
   adapter: postgresql
   encoding: unicode
   host: localhost
+  user: postgres
   # For details on connection pooling, see Rails configuration guide
   # https://guides.rubyonrails.org/configuring.html#database-pooling
   pool: <%= ENV.fetch("RAILS_MAX_THREADS") { 20 } %>

scripts/check_migrations.sh

@@ -0,0 +1,46 @@
+#!/bin/bash
+
+set -xuo pipefail
+# Check for new migrations
+versions=$(git diff --name-status remotes/origin/main demo/db/migrate/ | grep '^A' | cut -f2 | sed 's/[^0-9]//g' | sort -n --reverse)
+set -Ee # Enable failed command checks after checking
+
+if [ -z "$versions" ] ; then
+  echo "No changes to migrations."
+  exit 0
+fi
+
+# Replace schema.rb with one from main branch
+rm demo/db/schema.rb
+git checkout demo/db/schema.rb db/
+
+# Create database with schema from main branch
+bundle exec rake db:drop db:create
+bundle exec rake db:schema:load
+
+# Apply migrations and check that the generated schema.rb now matches the committed one
+bundle exec rake db:migrate
+if ! git diff --ignore-all-space --exit-code "HEAD" -- demo/db/schema.rb ; then
+  echo "Generated schema.rb does not match committed schema.rb"
+  exit 1
+fi
+
+# Run all migrations in reverse
+for version in $versions
+do
+  if grep -E 'raise (ActiveRecord::)?IrreversibleMigration' < "db/migrate/$version"* ; then
+    # One of the migrations explicitly uses IrreversibleMigration.
+    # Skip check for valid reversing
+    echo "Irreversible migration $version means we can't check for valid schema.rb; skipping"
+    exit 0
+  else
+    bundle exec rake db:migrate:down "VERSION=${version}"
+  fi
+done
+
+# Compare the resulting schema with
+bundle exec rake db:schema:dump
+if ! git diff --ignore-all-space --exit-code "$(git merge-base HEAD main)" -- demo/db/schema.rb ; then
+  echo "Some migrations could not be reversed cleanly, but do not reference IrreversibleMigration"
+  exit 1
+fi