Change the approach to check if patches apply cleanly

What does this MR do?

Are there points in the code the reviewer needs to double check?

Why was this MR needed?

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• CHANGELOG entry added
• Documentation created/updated
• API support added
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

Closes #23372 (closed)

lib/gitlab/ee_compat_check.rb

+module Gitlab
+  # Checks if a set of migrations requires downtime or not.
+  class EeCompatCheck
+    EE_REPO = 'https://gitlab.com/gitlab-org/gitlab-ee.git'.freeze
+
+    attr_reader :ce_branch, :check_dir, :ce_repo
+
+    def initialize(branch:, check_dir:, ce_repo: nil)
+      @ce_branch = branch
+      @check_dir = check_dir
+      @ce_repo = ce_repo || 'https://gitlab.com/gitlab-org/gitlab-ce.git'
+    end
+
+    def check
+      ensure_ee_repo
+      delete_patches
+
+      generate_patch(ce_branch, ce_patch_full_path)
+
+      Dir.chdir(check_dir) do
+        step("In the #{check_dir} directory")
+
+        step("Pulling latest master", %w[git pull --ff-only origin master])
+
+        status = catch(:halt_check) do
+          ce_branch_compat_check!
+
+          delete_ee_branch_locally
+
+          ee_branch_presence_check!
+
+          ee_branch_compat_check!
+        end
+
+        delete_ee_branch_locally
+        delete_patches
+
+        if status.nil?
+          puts
+          puts ee_applies_cleanly_msg
+          true
+        else
+          false
+        end
+      end
+    end
+
+    private
+
+    def ensure_ee_repo
+      if Dir.exist?(check_dir)
+        step("#{check_dir} already exists")
+      else
+        cmd = %W[git clone --branch master --single-branch --depth 1 #{EE_REPO} #{check_dir}]
+        step("Cloning #{EE_REPO} into #{check_dir}", cmd)
+      end
+    end
+
+    def ce_branch_compat_check!
+      cmd = %W[git apply --check #{ce_patch_full_path}]
+      status = step("Checking if #{ce_patch_name} applies cleanly to EE/master", cmd)
+
+      if status.zero?
+        puts ce_applies_cleanly_msg(ce_branch)
+        throw(:halt_check)
+      end
+    end
+
+    def ee_branch_presence_check!
+      status = step("Fetching origin/#{ee_branch}", %W[git fetch origin #{ee_branch}])
+
+      unless status.zero?
+        puts
+        puts ce_branch_doesnt_apply_cleanly_and_no_ee_branch_msg
+
+        throw(:halt_check, :ko)
+      end
+    end
+
+    def ee_branch_compat_check!
+      step("Checking out origin/#{ee_branch}", %W[git checkout -b #{ee_branch} FETCH_HEAD])
+
+      generate_patch(ee_branch, ee_patch_full_path)
+      cmd = %W[git apply --check #{ee_patch_full_path}]
+      status = step("Checking if #{ee_patch_name} applies cleanly to EE/master", cmd)
+
+      unless status.zero?
+        puts
+        puts ee_branch_doesnt_apply_cleanly_msg
+
+        throw(:halt_check, :ko)
+      end
+    end
+
+    def generate_patch(branch, filepath)
+      FileUtils.rm(filepath, force: true)
+
+      depth = 0
+      loop do
+        depth += 10
+        step("Fetching origin/master", %W[git fetch origin master --depth=#{depth}])
+        status = step("Finding merge base with master", %W[git merge-base FETCH_HEAD #{branch}])
+
+        break if status.zero? || depth > 500
+      end
+
+      raise "#{branch} is too far behind master, please rebase it!" if depth > 500
+
+      step("Generating the patch against master")
+      output, status = Gitlab::Popen.popen(%w[git format-patch FETCH_HEAD --stdout])
+      throw(:halt_check, :ko) unless status.zero?
+
+      File.open(filepath, 'w+') { |f| f.write(output) }
+      throw(:halt_check, :ko) unless File.exist?(filepath)
+    end
+
+    def delete_ee_branch_locally
+      step("Checking out origin/master", %w[git checkout master])
+      step("Deleting the local #{ee_branch} branch", %W[git branch -D #{ee_branch}])
+    end
+
+    def delete_patches
+      step("Deleting #{ce_patch_full_path}")
+      FileUtils.rm(ce_patch_full_path, force: true)
+
+      step("Deleting #{ee_patch_full_path}")
+      FileUtils.rm(ee_patch_full_path, force: true)
+    end
+
+    def ce_patch_name
+      @ce_patch_name ||= "#{ce_branch}.patch"
+    end
+
+    def ce_patch_full_path
+      @ce_patch_full_path ||= File.expand_path(ce_patch_name, check_dir)
+    end
+
+    def ee_branch
+      @ee_branch ||= "#{ce_branch}-ee"
+    end
+
+    def ee_patch_name
+      @ee_patch_name ||= "#{ee_branch}.patch"
+    end
+
+    def ee_patch_full_path
+      @ee_patch_full_path ||= File.expand_path(ee_patch_name, check_dir)
+    end
+
+    def step(desc, cmd = nil)
+      puts "\n=> #{desc}\n"
+
+      if cmd
+        puts "\n$ #{cmd.join(' ')}"
+        command(cmd)
+      end
+    end
+
+    def command(cmd)
+      output, status = Gitlab::Popen.popen(cmd)
+      puts output
+
+      status
+    end
+
+    def ce_applies_cleanly_msg(ce_branch)
+      <<-MSG.strip_heredoc
+        =================================================================
+        🎉 Congratulations!! 🎉
+
+        The #{ce_branch} branch applies cleanly to EE/master!
+
+        Much ❤️!!
+        =================================================================\n
+      MSG
+    end
+
+    def ce_branch_doesnt_apply_cleanly_and_no_ee_branch_msg
+      <<-MSG.strip_heredoc
+        =================================================================
+        💥 Oh no! 💥
+
+        The #{ce_branch} branch does not apply cleanly to the current
+        EE/master, and no #{ee_branch} branch was found in the EE repository.
+
+        Please create a #{ee_branch} branch that includes changes from
+        #{ce_branch} but also specific changes than can be applied cleanly
+        to EE/master.
+
+        There are different ways to create such branch:
+
+        1. Create a new branch based on the CE branch and rebase it on top of EE/master
+
+          # In the EE repo
+          $ git fetch #{ce_repo} #{ce_branch}
+          $ git checkout -b #{ee_branch} FETCH_HEAD
+
+          # You can squash the #{ce_branch} commits into a single "Port of #{ce_branch} to EE" commit
+          # before rebasing to limit the conflicts-resolving steps during the rebase
+          $ git fetch origin
+          $ git rebase origin/master
+
+          At this point you will likely have conflicts.
+          Solve them, and continue/finish the rebase.
+
+          You can squash the #{ce_branch} commits into a single "Port of #{ce_branch} to EE".
+
+        2. Create a new branch from master and cherry-pick your CE commits
+
+          # In the EE repo
+          $ git fetch origin
+          $ git checkout -b #{ee_branch} FETCH_HEAD
+          $ git fetch #{ce_repo} #{ce_branch}
+          $ git cherry-pick SHA # Repeat for all the commits you want to pick
+
+          You can squash the #{ce_branch} commits into a single "Port of #{ce_branch} to EE" commit.
+
+        3. Generate a patch from your CE branch and apply it in a new EE branch
+
+          # In the CE repo
+          $ git fetch origin master
+          $ git format-patch FETCH_HEAD --stdout > ~/#{ce_branch}.patch
+
+          # In the EE repo
+          $ git fetch origin master
+          $ git checkout -b #{ee_branch} FETCH_HEAD
+          $ git apply ~/#{ce_branch}.patch
+
+          At this point you will likely have conflicts.
+          Solve them, and create a new "Port of #{ce_branch} to EE" commit.
+
+        Don't forget to push your branch to #{EE_REPO}:
+
+          # In the EE repo
+          $ git push origin #{ee_branch}
+
+        You can then retry this failed build, and hopefully it should pass.
+
+        Stay 💪 !
+        =================================================================\n
+      MSG
+    end
+
+    def ee_branch_doesnt_apply_cleanly_msg
+      <<-MSG.strip_heredoc
+        =================================================================
+        💥 Oh no! 💥
+
+        The #{ce_branch} does not apply cleanly to the current
+        EE/master, and even though a #{ee_branch} branch exists in the EE
+        repository, it does not apply cleanly either to EE/master!
+
+        Please update the #{ee_branch}, push it again to #{EE_REPO}, and
+        retry this build.
+
+        Stay 💪 !
+        =================================================================\n
+      MSG
+    end
+
+    def ee_applies_cleanly_msg
+      <<-MSG.strip_heredoc
+        =================================================================
+        🎉 Congratulations!! 🎉
+
+        The #{ee_branch} branch applies cleanly to EE/master!
+
+        Much ❤️!!
+        =================================================================\n
+      MSG
+    end
+  end
+end