Add `SKIP_DATABASE_CONFIG_VALIDATION` env

This allows to disable all transformation
and validation of database config.

config/application.rb

@@ -39,7 +39,9 @@ module Gitlab
     # This preload is needed to convert legacy `database.yml`
     # from `production: adapter: postgresql`
     # into a `production: main: adapter: postgresql`
-    config.class.prepend(::Gitlab::Patch::LegacyDatabaseConfig)
+    unless Gitlab::Utils.to_boolean(ENV['SKIP_DATABASE_CONFIG_VALIDATION'], default: false)
+      config.class.prepend(::Gitlab::Patch::LegacyDatabaseConfig)
+    end
 
     # Settings in config/environments/* take precedence over those specified here.
     # Application configuration should go into files in config/initializers

config/initializers/validate_database_config.rb

 # frozen_string_literal: true
 
+if Gitlab::Utils.to_boolean(ENV['SKIP_DATABASE_CONFIG_VALIDATION'], default: false)
+  return
+end
+
 if Rails.application.config.uses_legacy_database_config
   warn "WARNING: This installation of GitLab uses a deprecated syntax for 'config/database.yml'. " \
     "The support for this syntax will be removed in 15.0. " \

spec/initializers/validate_database_config_spec.rb

@@ -3,6 +3,9 @@
 require 'spec_helper'
 
 RSpec.describe 'validate database config' do
+  include RakeHelpers
+  include StubENV
+
   let(:rails_configuration) { Rails::Application::Configuration.new(Rails.root) }
   let(:ar_configurations) { ActiveRecord::DatabaseConfigurations.new(rails_configuration.database_configuration) }
 
@@ -18,8 +21,18 @@ RSpec.describe 'validate database config' do
       .to receive(:read).with(Rails.root.join('config/database.yml')).and_return(database_yml)
     # rubocop:enable RSpec/AnyInstanceOf
 
-    allow(Rails.application).to receive(:configuration) { rails_configuration }
-    allow(ActiveRecord::Base).to receive(:configurations) { ar_configurations }
+    allow(Rails.application).to receive(:config).and_return(rails_configuration)
+    allow(ActiveRecord::Base).to receive(:configurations).and_return(ar_configurations)
+  end
+
+  shared_examples 'with SKIP_DATABASE_CONFIG_VALIDATION=true' do
+    before do
+      stub_env('SKIP_DATABASE_CONFIG_VALIDATION', 'true')
+    end
+
+    it 'does not raise exception' do
+      expect { subject }.not_to raise_error
+    end
   end
 
   context 'when config/database.yml is valid' do
@@ -37,10 +50,12 @@ RSpec.describe 'validate database config' do
       end
 
       it 'validates configuration with a warning' do
-        expect(Kernel).not_to receive(:warn).with /uses a deprecated syntax for/
+        expect(main_object).to receive(:warn).with /uses a deprecated syntax for/
 
         expect { subject }.not_to raise_error
       end
+
+      it_behaves_like 'with SKIP_DATABASE_CONFIG_VALIDATION=true'
     end
 
     context 'uses new syntax' do
@@ -58,7 +73,7 @@ RSpec.describe 'validate database config' do
       end
 
       it 'validates configuration without errors and warnings' do
-        expect(Kernel).not_to receive(:warn)
+        expect(main_object).not_to receive(:warn)
 
         expect { subject }.not_to raise_error
       end
@@ -91,6 +106,8 @@ RSpec.describe 'validate database config' do
       it 'raises exception' do
         expect { subject }.to raise_error /This installation of GitLab uses unsupported database names/
       end
+
+      it_behaves_like 'with SKIP_DATABASE_CONFIG_VALIDATION=true'
     end
 
     context 'uses replica configuration' do
@@ -111,6 +128,8 @@ RSpec.describe 'validate database config' do
       it 'raises exception' do
         expect { subject }.to raise_error /with 'replica: true' parameter in/
       end
+
+      it_behaves_like 'with SKIP_DATABASE_CONFIG_VALIDATION=true'
     end
 
     context 'main is not a first entry' do
@@ -140,6 +159,8 @@ RSpec.describe 'validate database config' do
       it 'raises exception' do
         expect { subject }.to raise_error /The `main:` database needs to be defined as a first configuration item/
       end
+
+      it_behaves_like 'with SKIP_DATABASE_CONFIG_VALIDATION=true'
     end
   end
 end