Make Bootsnap available via ENABLE_BOOTSNAP=1

Bootsnap speeds up Rails loading and now ships by default with Rails 5.2
apps. We should promote this to a default gem and test it out in
production. This will also make it possible for the Helm Charts to take
advantage of this.

It appears that Bootsnap with Rails 5.2.3 and all the GitLab CE gems
loads fine on an ARM platform now, so it's possible that
https://gitlab.com/gitlab-org/gitlab-ce/issues/34799 has been resolved.

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/45230

.gitlab/ci/memory.gitlab-ci.yml

@@ -33,7 +33,7 @@ memory-on-boot:
     NODE_OPTIONS: --max_old_space_size=3584
   script:
     # Both bootsnap and derailed monkey-patch Kernel#require, which leads to circular dependency
-    - DISABLE_BOOTSNAP=true PATH_TO_HIT="/users/sign_in" CUT_OFF=0.3 bundle exec derailed exec perf:mem >> 'tmp/memory_on_boot.txt'
+    - ENABLE_BOOTSNAP=false PATH_TO_HIT="/users/sign_in" CUT_OFF=0.3 bundle exec derailed exec perf:mem >> 'tmp/memory_on_boot.txt'
     - scripts/generate-memory-metrics-on-boot tmp/memory_on_boot.txt >> 'tmp/memory_on_boot_metrics.txt'
   artifacts:
     paths:

Gemfile

@@ -2,6 +2,8 @@ source 'https://rubygems.org'
 gem 'rails', '5.2.3'
+gem 'bootsnap', '~> 1.4'
+
 # Improves copy-on-write performance for MRI
 gem 'nakayoshi_fork', '~> 0.0.4'
@@ -329,7 +331,6 @@ group :development do
 end
 group :development, :test do
-  gem 'bootsnap', '~> 1.4'
   gem 'bullet', '~> 5.5.0', require: !!ENV['ENABLE_BULLET']
   gem 'pry-byebug', '~> 3.5.1', platform: :mri
   gem 'pry-rails', '~> 0.3.4'

Gemfile.lock

@@ -100,7 +100,7 @@ GEM
     binding_ninja (0.2.3)
     binding_of_caller (0.8.0)
       debug_inspector (>= 0.0.1)
-    bootsnap (1.4.1)
+    bootsnap (1.4.4)
       msgpack (~> 1.0)
     bootstrap_form (4.2.0)
       actionpack (>= 5.0)
@@ -529,7 +529,7 @@ GEM
     mixlib-cli (1.7.0)
     mixlib-config (2.2.18)
       tomlrb
-    msgpack (1.2.10)
+    msgpack (1.3.0)
     multi_json (1.13.1)
     multi_xml (0.6.0)
     multipart-post (2.0.0)

changelogs/unreleased/sh-enable-bootsnap.yml

+---
+title: Make Bootsnap available via ENABLE_BOOTSNAP=1
+merge_request: 30963
+author:
+type: performance

config/boot.rb

@@ -3,7 +3,7 @@ ENV['BUNDLE_GEMFILE'] ||= File.expand_path('../Gemfile', __dir__)
 # Set up gems listed in the Gemfile.
 require 'bundler/setup' if File.exist?(ENV['BUNDLE_GEMFILE'])
 begin
-  require 'bootsnap/setup' unless ENV['DISABLE_BOOTSNAP']
+  require 'bootsnap/setup' if ENV['RAILS_ENV'] != 'production' || %w(1 yes true).include?(ENV['ENABLE_BOOTSNAP'])
 rescue LoadError
   # bootsnap is an optional dependency, so if we don't have it, it's fine
 end