Fix foreign key and index names in `ci_sources_pipelines`

When the `ci_sources_pipelines` table was first introduced in GitLab 9.3
EE, the foreign key names generate for the table appeared to have been
calculated via a hash using the table name
`ci_pipeline_source_pipelines`. This led to a merge conflict and
confusion during a CE to EE merge in GitLab 10.0, which regenerated the
schema with the correct foreign key names.

Hence anyone who installed GitLab prior to 10.0 may have been seeded the
database with stale, incorrect foreign key names.

During the Great BigInt Conversion of 2021, the migrations assumed that:

1. The foreign key `fk_be5624bf37` existed for `ci_sources_pipelines`.
2. The index `index_ci_sources_pipelines_on_source_job_id` existed.

However, older installations may have had the foreign key under the
original `fk_3f0c88d7dc` and
`index_ci_pipeline_source_pipelines_on_source_job_id`, respectively.

To eliminate future confusion and migration failures, we now rename the
foreign key constraints and index to what they should be today.

Relates to https://gitlab.com/gitlab-org/gitlab/-/issues/339844

Changelog: fixed

db/post_migrate/20210713042000_fix_ci_sources_pipelines_index_names.rb

+# frozen_string_literal: true
+
+# When the `ci_sources_pipelines` table was first introduced in GitLab
+# 9.3 EE, the foreign key names generate for the table appeared to
+# have been calculated via a hash using the table name
+# `ci_pipeline_source_pipelines`. This led to a merge conflict and
+# confusion during a CE to EE merge in GitLab 10.0, which regenerated
+# the schema with the correct foreign key names.
+#
+# Hence anyone who installed GitLab prior to 10.0 may have been seeded
+# the database with stale, incorrect foreign key names.
+#
+# During the Great BigInt Conversion of 2021, several migrations
+# assumed that the foreign key `fk_be5624bf37` existed for
+# `ci_sources_pipeline`. However, older installations may have had the
+# correct foreign key under the name `fk_3f0c88d7dc`.
+#
+# To eliminate future confusion and migration failures, we now rename
+# the foreign key constraints and index to what they should be today.
+class FixCiSourcesPipelinesIndexNames < ActiveRecord::Migration[6.1]
+  include Gitlab::Database::MigrationHelpers
+
+  disable_ddl_transaction!
+
+  TABLE_NAME = 'ci_sources_pipelines'
+
+  # GitLab 9.5.4: https://gitlab.com/gitlab-org/gitlab/-/blob/v9.5.4-ee/db/schema.rb#L2026-2030
+  # GitLab 10.0: https://gitlab.com/gitlab-org/gitlab/-/blob/v10.0.0-ee/db/schema.rb#L2064-2068
+  OLD_TO_NEW_FOREIGN_KEY_DEFS = {
+    'fk_3f0c88d7dc' => { table: :ci_builds, column: :source_job_id, name: 'fk_be5624bf37' },
+    'fk_b8c0fac459' => { table: :ci_pipelines, column: :pipeline_id, name: 'fk_e1bad85861' },
+    'fk_3a3e3cb83a' => { table: :ci_pipelines, column: :source_pipeline_id, name: 'fk_d4e29af7d7' },
+    'fk_8868d0f3e4' => { table: :projects, column: :source_project_id, name: 'fk_acd9737679' },
+    'fk_83b4346e48' => { table: :projects, name: 'fk_1e53c97c0a' }
+  }
+  OLD_INDEX_NAME = 'index_ci_pipeline_source_pipelines_on_source_job_id'
+  NEW_INDEX_NAME = 'index_ci_sources_pipelines_on_source_job_id'
+
+  def up
+    OLD_TO_NEW_FOREIGN_KEY_DEFS.each do |old_name, entry|
+      options = { column: entry[:column], name: old_name }.compact
+
+      if foreign_key_exists?(TABLE_NAME, entry[:table], **options)
+        rename_constraint(TABLE_NAME, old_name, entry[:name])
+      end
+    end
+
+    if index_exists_by_name?(TABLE_NAME, OLD_INDEX_NAME)
+      if index_exists_by_name?(TABLE_NAME, NEW_INDEX_NAME)
+        remove_concurrent_index_by_name(TABLE_NAME, OLD_INDEX_NAME)
+      else
+        rename_index(TABLE_NAME, OLD_INDEX_NAME, NEW_INDEX_NAME)
+      end
+    end
+  end
+
+  # There's no reason to revert this change since it should apply on stale schemas
+  def down; end
+end

db/schema_migrations/20210713042000

+ede336cca4f5d692fb9fccb60db7846a917d887412a10699e818a6caf0ef6a45
\ No newline at end of file

spec/migrations/20210713042000_fix_ci_sources_pipelines_index_names_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+require_migration!
+
+RSpec.describe FixCiSourcesPipelinesIndexNames, :migration do
+  def validate_foreign_keys_and_index!
+    aggregate_failures do
+      expect(subject.foreign_key_exists?(:ci_sources_pipelines, :ci_builds, column: :source_job_id, name: 'fk_be5624bf37')).to be_truthy
+      expect(subject.foreign_key_exists?(:ci_sources_pipelines, :ci_pipelines, column: :pipeline_id, name: 'fk_e1bad85861')).to be_truthy
+      expect(subject.foreign_key_exists?(:ci_sources_pipelines, :ci_pipelines, column: :source_pipeline_id, name: 'fk_d4e29af7d7')).to be_truthy
+      expect(subject.foreign_key_exists?(:ci_sources_pipelines, :projects, column: :source_project_id, name: 'fk_acd9737679')).to be_truthy
+      expect(subject.foreign_key_exists?(:ci_sources_pipelines, :projects, name: 'fk_1e53c97c0a')).to be_truthy
+      expect(subject.foreign_key_exists?(:ci_sources_pipelines, :ci_builds, column: :source_job_id_convert_to_bigint, name: 'fk_be5624bf37_tmp')).to be_falsey
+
+      expect(subject.index_exists_by_name?(:ci_sources_pipelines, described_class::NEW_INDEX_NAME)).to be_truthy
+      expect(subject.index_exists_by_name?(:ci_sources_pipelines, described_class::OLD_INDEX_NAME)).to be_falsey
+    end
+  end
+
+  it 'existing foreign keys and indexes are untouched' do
+    validate_foreign_keys_and_index!
+
+    migrate!
+
+    validate_foreign_keys_and_index!
+  end
+
+  context 'with a legacy (pre-GitLab 10.0) foreign key' do
+    let(:old_foreign_keys) { described_class::OLD_TO_NEW_FOREIGN_KEY_DEFS.keys }
+    let(:new_foreign_keys) { described_class::OLD_TO_NEW_FOREIGN_KEY_DEFS.values.map { |entry| entry[:name] } }
+
+    before do
+      new_foreign_keys.each { |name| subject.remove_foreign_key_if_exists(:ci_sources_pipelines, name: name) }
+
+      # GitLab 9.5.4: https://gitlab.com/gitlab-org/gitlab/-/blob/v9.5.4-ee/db/schema.rb#L2026-2030
+      subject.add_foreign_key(:ci_sources_pipelines, :ci_builds, column: :source_job_id, name: 'fk_3f0c88d7dc', on_delete: :cascade)
+      subject.add_foreign_key(:ci_sources_pipelines, :ci_pipelines, column: :pipeline_id, name: "fk_b8c0fac459", on_delete: :cascade)
+      subject.add_foreign_key(:ci_sources_pipelines, :ci_pipelines, column: :source_pipeline_id, name: "fk_3a3e3cb83a", on_delete: :cascade)
+      subject.add_foreign_key(:ci_sources_pipelines, :projects, column: :source_project_id, name: "fk_8868d0f3e4", on_delete: :cascade)
+      subject.add_foreign_key(:ci_sources_pipelines, :projects, name: "fk_83b4346e48", on_delete: :cascade)
+
+      # https://gitlab.com/gitlab-org/gitlab/-/blob/v9.5.4-ee/db/schema.rb#L443
+      subject.add_index "ci_sources_pipelines", ["source_job_id"], name: described_class::OLD_INDEX_NAME, using: :btree
+    end
+
+    context 'when new index already exists' do
+      it 'corrects foreign key constraints and drops old index' do
+        expect { migrate! }.to change { subject.foreign_key_exists?(:ci_sources_pipelines, :ci_builds, column: :source_job_id, name: 'fk_3f0c88d7dc') }.from(true).to(false)
+
+        validate_foreign_keys_and_index!
+      end
+    end
+
+    context 'when new index does not exist' do
+      before do
+        subject.remove_index("ci_sources_pipelines", name: described_class::NEW_INDEX_NAME)
+      end
+
+      it 'drops the old index' do
+        expect { migrate! }.to change { subject.index_exists_by_name?(:ci_sources_pipelines, described_class::OLD_INDEX_NAME) }.from(true).to(false)
+
+        validate_foreign_keys_and_index!
+      end
+    end
+  end
+end