From 9f0b8eb5843b8f8db19440fcb1962727f655eed1 Mon Sep 17 00:00:00 2001
From: John Hawthorn <john@hawthorn.email>
Date: Mon, 17 Jan 2022 10:49:31 -0800
Subject: [PATCH] Deprecate Event#{children,parent_of}

---
 activesupport/CHANGELOG.md                    |  2 ++
 .../notifications/instrumenter.rb             | 28 ++++++++++++-------
 activesupport/test/notifications_test.rb      | 15 ----------
 3 files changed, 20 insertions(+), 25 deletions(-)

diff --git a/activesupport/CHANGELOG.md b/activesupport/CHANGELOG.md
index 1d4f2f64de..8507a00a05 100644
--- a/activesupport/CHANGELOG.md
+++ b/activesupport/CHANGELOG.md
@@ -1,3 +1,5 @@
+*   Deprecate `Notification::Event`'s `#children` and `#parent_of?`
+
 *   Change default serialization format of `MessageEncryptor` from `Marshal` to `JSON` for Rails 7.1.
 
     Existing apps are provided with an upgrade path to migrate to `JSON` as described in `guides/source/upgrading_ruby_on_rails.md`
diff --git a/activesupport/lib/active_support/notifications/instrumenter.rb b/activesupport/lib/active_support/notifications/instrumenter.rb
index c69e8cd8d4..867cb7c6ef 100644
--- a/activesupport/lib/active_support/notifications/instrumenter.rb
+++ b/activesupport/lib/active_support/notifications/instrumenter.rb
@@ -56,7 +56,7 @@ module ActiveSupport
     end
 
     class Event
-      attr_reader :name, :time, :end, :transaction_id, :children
+      attr_reader :name, :time, :end, :transaction_id
       attr_accessor :payload
 
       def initialize(name, start, ending, transaction_id, payload)
@@ -65,7 +65,6 @@ module ActiveSupport
         @time           = start ? start.to_f * 1_000.0 : start
         @transaction_id = transaction_id
         @end            = ending ? ending.to_f * 1_000.0 : ending
-        @children       = []
         @cpu_time_start = 0.0
         @cpu_time_finish = 0.0
         @allocation_count_start = 0
@@ -117,6 +116,23 @@ module ActiveSupport
         @allocation_count_finish - @allocation_count_start
       end
 
+      def children # :nodoc:
+        ActiveSupport::Deprecation.warn <<~EOM
+          ActiveSupport::Notifications::Event#children is deprecated and will
+          be removed in Rails 7.2.
+        EOM
+        []
+      end
+
+      def parent_of?(event) # :nodoc:
+        ActiveSupport::Deprecation.warn <<~EOM
+          ActiveSupport::Notifications::Event#parent_of? is deprecated and will
+          be removed in Rails 7.2.
+        EOM
+        start = (time - event.time) * 1000
+        start <= 0 && (start + duration >= event.duration)
+      end
+
       # Returns the difference in milliseconds between when the execution of the
       # event started and when it ended.
       #
@@ -133,14 +149,6 @@ module ActiveSupport
         self.end - time
       end
 
-      def <<(event)
-        @children << event
-      end
-
-      def parent_of?(event)
-        @children.include? event
-      end
-
       private
         def now
           Process.clock_gettime(Process::CLOCK_MONOTONIC, :float_millisecond)
diff --git a/activesupport/test/notifications_test.rb b/activesupport/test/notifications_test.rb
index 2964e752dc..775c470862 100644
--- a/activesupport/test/notifications_test.rb
+++ b/activesupport/test/notifications_test.rb
@@ -462,21 +462,6 @@ module Notifications
       assert_equal Hash[payload: :bar], event.payload
     end
 
-    def test_event_is_parent_based_on_children
-      time = Process.clock_gettime(Process::CLOCK_MONOTONIC)
-
-      parent    = event(:foo, Process.clock_gettime(Process::CLOCK_MONOTONIC), Process.clock_gettime(Process::CLOCK_MONOTONIC) + 100, random_id, {})
-      child     = event(:foo, time, time + 10, random_id, {})
-      not_child = event(:foo, time, time + 100, random_id, {})
-
-      parent.children << child
-
-      assert parent.parent_of?(child)
-      assert_not child.parent_of?(parent)
-      assert_not parent.parent_of?(not_child)
-      assert_not not_child.parent_of?(parent)
-    end
-
     def test_subscribe_raises_error_on_non_supported_arguments
       notifier = ActiveSupport::Notifications::Fanout.new