Merge remote-tracking branch 'upstream/master' into pr-5048

* upstream/master: (27 commits)
  Create security policy following github's template (mongodb#5070)
  MONGOID-5131 Use proper mdb <-> ubuntu versions (mongodb#5067)
  MONGOID-5131: Set up build pipeline for outside contributors (mongodb#5043)
  MONGOID-5165 Fix documentation link (mongodb#5065)
  Fix indentation
  MONGOID-5029 #empty method should use an #exists? rather than a #count query (mongodb#5029)
  MONGOID-5177 Fix flaky contextual spec (mongodb#5064)
  MONGOID-5170 - Fix more typos mostly in code docs and code comments (mongodb#5056)
  MONGOID-5105 Allow block form in Mongoid::Association::EmbedsMany::Proxy#count  (mongodb#5060)
  MONGOID-5162 Add a release note for the planned changes in ObjectId#as_json (mongodb#5059)
  MONGOID-5171 - Make the minimum Ruby version 2.5 (mongodb#5058)
  MONGOID-5130 Remove conn count from client spec (mongodb#5055)
  Add driver 2.15 to compat table
  Fix MONGOID-5136 .touch with custom field is broken for embedded documents (mongodb#5039)
  MONGOID-5144 Add a deprecation warning when using the legacy query cache (mongodb#5042)
  MONGOID-???? Replace field[0] == ?$ with field.start_with?('$') -- easier to read and 30%+ faster (mongodb#5052)
  MONGOID-???? - Remove BSON::ObjectId#as_json as we will defer to the bson-ruby gem implementation. (mongodb#5057)
  MONGOID-4737 Deprecate the :compact option on Document#as_json (mongodb#5040)
  MONGOID-5143 [Code Comments Only] Remove magic comment "# encoding: utf-8" (mongodb#5041)
  Remove all @SInCE comments. These are generally not useful as: (mongodb#5037)
  ...

.evergreen/make-github-actions

@@ -0,0 +1,288 @@
+#!/usr/bin/env ruby
+
+# TODO: Support topology=sharded-cluster (requires better MongoDB Github Action)
+# TODO: Support i18n-fallbacks test
+# TODO: Support app-tests tests
+
+require 'fileutils'
+require 'active_support/dependencies/autoload'
+require 'active_support/core_ext'
+require 'yaml'
+
+class YamlConfig
+  def data
+    @data ||= YAML.load(File.read(path)).deep_symbolize_keys
+  end
+end
+
+class EvergreenConfig < YamlConfig
+
+  def matrix_axes
+    data[:axes].each_with_object({}) do |axis, node|
+      node[axis[:id].underscore] = axis[:values].pluck(:id)
+    end
+  end
+
+  def axes
+    @axes ||= data[:axes].each_with_object({}) do |axis, node|
+      node[axis[:id].underscore.to_sym] = axis[:values].pluck(:id)
+    end
+  end
+
+  def variants
+    @variants ||= data[:buildvariants].each_with_object([]) do |var, nodes|
+      name = var[:matrix_name]
+
+      spec = var[:matrix_spec]
+      tasks = var[:tasks]&.pluck(:name)
+      raise("Invalid Evergreen buildvariant '#{name}'. Value for 'tasks' is empty.") unless tasks.present?
+      raise("Unsupported Evergreen buildvariant '#{name}'. Cannot have more than one item in 'tasks'.") unless tasks.size == 1
+
+      node = {
+        # matrix_name:  name,
+        # display_name: var[:display_name],
+        mongodb:  spec[:'mongodb-version'],
+        ruby:     spec[:jruby] || spec[:ruby],
+        topology: spec[:topology],
+        task:     tasks.first,
+
+        # these will be later mapped to gemfile
+        driver: spec[:driver],
+        rails:  spec[:rails],
+        i18n:   spec[:i18n],
+      }
+
+      missing = node.map {|k, v| k if v.blank? }.compact
+      missing -= %i[driver rails i18n]
+
+      if missing.present?
+        puts "Skipping invalid Evergreen buildvariant '#{name}'. Keys missing: #{missing}"
+        next
+      end
+
+      nodes << node
+    end
+  end
+
+  protected
+
+  def path
+    File.join(File.dirname(__FILE__), 'config.yml')
+  end
+end
+
+class GithubConfig < YamlConfig
+
+  def write(data)
+    FileUtils.mkdir_p(File.dirname(path))
+    data = data.deep_stringify_keys
+    File.open(path, 'w+') {|f| f.write((comment || '') + data.to_yaml) }
+    @data = data
+  end
+
+  private
+
+  def path
+    File.join(File.dirname(__FILE__), '../.github/workflows/test.yml')
+  end
+
+  def comment
+    <<~COMMENT
+      # This file was auto-generated by .evergreen/make-github-actions
+      # at #{Time.now.utc.rfc3339}
+    COMMENT
+  end
+end
+
+class Transmogrifier
+  SPLATTABLE_FIELDS  = %i[mongodb topology ruby rails driver i18n]
+  COMPACTABLE_FIELDS = %i[mongodb topology ruby gemfile]
+
+  attr_reader :eg_config,
+              :gh_config
+
+  def initialize
+    @eg_config = EvergreenConfig.new
+    @gh_config = GithubConfig.new
+  end
+
+  def transmogrify!
+    gh_config.write(root_node)
+    print_stats
+  end
+
+  delegate :variants,
+           :axes,
+           to: :eg_config
+
+  def root_node
+    {
+      name: 'Run Mongoid Tests',
+      on: %w[push pull_request],
+      jobs: {
+        build: {
+          name: '${{matrix.ruby}} driver-${{matrix.driver}} mongodb-${{matrix.mongodb}} ${{matrix.topology}}',
+          env: {
+            CI: true,
+            TESTOPTS: "-v"
+          },
+          'runs-on': 'ubuntu-latest',
+          'continue-on-error': "${{matrix.experimental}}",
+          strategy: {
+            'fail-fast': false,
+            matrix: { include: inclusions_node } },
+          steps: steps_node
+        }
+      }
+    }
+  end
+
+  def print_stats
+    puts "#{inclusions_node.size} unique matrix builds written"
+  end
+
+  def inclusions_node
+    @inclusions_node ||= begin
+      inclusions = splat(variants).each {|node| transform_node!(node) }.reject {|node| unsupported?(node) }
+      puts "#{inclusions.size} candidate matrix builds identified"
+      compact_nodes(inclusions)
+    end
+  end
+
+  def compact_nodes(nodes)
+    nodes.each_with_object({}) do |node, uniq_nodes|
+      key = COMPACTABLE_FIELDS.map {|k| "#{k}:#{node[k]}" }.join('|')
+      uniq_nodes[key] ||= node
+    end.values
+  end
+
+  def splat(array)
+    # array
+    SPLATTABLE_FIELDS.each do |field|
+      array = array.each_with_object([]) do |node, new_array|
+        case node[field]
+        when Array
+          node[field].each do |val|
+            new_array << node.dup.tap {|n| n[field] = val }
+          end
+        when '*'
+          axes[field].each do |val|
+            new_array << node.dup.tap {|n| n[field] = val }
+          end
+        else
+          new_array << node
+        end
+      end
+    end
+    array
+  end
+
+  def unsupported?(node)
+    node[:topology] == 'sharded_cluster'
+  end
+
+  def transform_node!(node)
+    node[:topology] = case node[:topology]
+                        when 'replica-set'
+                          'replica_set'
+                        when 'sharded-cluster'
+                          'sharded_cluster'
+                        else
+                          'server'
+                      end
+    extract_gemfile!(node)
+    set_experimental!(node)
+  end
+
+  def set_experimental!(node)
+    node[:experimental] = node[:gemfile].match?(/master|main|head/)
+  end
+
+  def extract_gemfile!(node)
+    node[:gemfile] = get_gemfile(*node.values_at(:driver, :rails, :i18n))
+  end
+
+  # Ported from run-tests.sh
+  def get_gemfile(driver, rails, i18n)
+    driver, rails, i18n = [driver, rails, i18n].map {|v| v&.to_s }
+    if driver && driver != 'current'
+      "gemfiles/driver_#{driver.underscore}.gemfile"
+    elsif rails && rails != '6.1' # TODO: "6.1" should be renamed to "current" in Evergreen
+      "gemfiles/rails-#{rails}.gemfile"
+    elsif i18n && i18n == '1.0'
+      'gemfiles/i18n-1.0.gemfile'
+    else
+      'Gemfile'
+    end
+  end
+
+  def ruby_env
+    {}
+  end
+
+  def steps_node
+    [ step_checkout,
+      step_mongodb,
+      step_ruby,
+      step_bundle,
+      step_test ]
+  end
+
+  def step_checkout
+    {
+      name: "repo checkout",
+      uses: "actions/checkout@v2",
+      with: {
+        submodules: "recursive"
+      }
+    }
+  end
+
+  def step_mongodb
+    {
+      id: "start-mongodb"
+      name: "start mongodb",
+      uses: "mongodb-labs/drivers-evergreen-tools@master",
+      with: {
+        'version': '${{matrix.mongodb}}',
+        'topology': '${{matrix.topology}}'
+      }
+    }
+  end
+
+  def step_ruby
+    {
+      name: "load ruby",
+      uses: "ruby/setup-ruby@v1",
+      env: step_ruby_env,
+      with: {
+        'ruby-version': "${{matrix.ruby}}",
+        bundler: 2
+      }
+    }
+  end
+
+  def step_bundle
+    {
+      name: 'bundle',
+      run: 'bundle install --jobs 4 --retry 3',
+      env: step_ruby_env
+    }
+  end
+
+  def step_test
+    {
+      name: 'test',
+      "timeout-minutes": 60,
+      "continue-on-error": '${{matrix.experimental}}',
+      run: 'bundle exec rake spec',
+      env: step_ruby_env.merge({'MONGODB_URI': "${{ steps.start-mongodb.outputs.cluster-uri }}"})
+    }
+  end
+
+  def step_ruby_env
+    { 'BUNDLE_GEMFILE': '${{matrix.gemfile}}' }
+  end
+end
+
+Transmogrifier.new.transmogrify!