From 46b996c24da17cdc7a16bc3037edab5c6132ccd0 Mon Sep 17 00:00:00 2001
From: "github-actions[bot]"
 <41898282+github-actions[bot]@users.noreply.github.com>
Date: Wed, 24 Jul 2024 10:29:18 +0100
Subject: [PATCH] settings: add support for observing settings after
 post-process hooks (#16339) (#16348)

Because logging configuration occurs after loading the `logstash.yml`
settings, deprecation logs from `LogStash::Settings::DeprecatedAlias#set` are
effectively emitted to a null logger and lost.

By re-emitting after the post-process hooks, we can ensure that they make
their way to the deprecation log. This change adds support for any setting
that responds to `Object#observe_post_process` to receive it after all
post-processing hooks have been executed.

Resolves: elastic/logstash#16332
(cherry picked from commit c633ad25682f3376adb0ba434d658b9eb820ac92)

Co-authored-by: Ry Biesemeyer <yaauie@users.noreply.github.com>
---
 logstash-core/lib/logstash/settings.rb        | 23 ++++++++++++++++---
 .../setting_with_deprecated_alias_spec.rb     | 21 +++++++++++++++++
 logstash-core/spec/logstash/settings_spec.rb  | 12 ++++++++++
 3 files changed, 53 insertions(+), 3 deletions(-)

diff --git a/logstash-core/lib/logstash/settings.rb b/logstash-core/lib/logstash/settings.rb
index 4e23e34c3a9..d6238fe1cb0 100644
--- a/logstash-core/lib/logstash/settings.rb
+++ b/logstash-core/lib/logstash/settings.rb
@@ -197,6 +197,13 @@ def post_process
           callback.call(self)
         end
       end
+
+      # because we cannot rely on deprecation logger being wired up when the setters
+      # are initially used, we re-emit setter-related deprecations after all post-processing
+      # hooks have been activated (and therefore after logging has been configured)
+      @settings.each_value do |setting|
+        setting.observe_post_process if setting.respond_to?(:observe_post_process)
+      end
     end
 
     def on_post_process(&block)
@@ -839,9 +846,7 @@ def initialize(canonical_proxy, alias_name)
       end
 
       def set(value)
-        deprecation_logger.deprecated(I18n.t("logstash.settings.deprecation.set",
-                                             :deprecated_alias => name,
-                                             :canonical_name => canonical_proxy.name))
+        do_log_setter_deprecation
         super
       end
 
@@ -856,6 +861,18 @@ def validate_value
         # bypass deprecation warning
         wrapped.validate_value if set?
       end
+
+      def observe_post_process
+        do_log_setter_deprecation if set?
+      end
+
+      private
+
+      def do_log_setter_deprecation
+        deprecation_logger.deprecated(I18n.t("logstash.settings.deprecation.set",
+                                             :deprecated_alias => name,
+                                             :canonical_name => canonical_proxy.name))
+      end
     end
 
     ##
diff --git a/logstash-core/spec/logstash/settings/setting_with_deprecated_alias_spec.rb b/logstash-core/spec/logstash/settings/setting_with_deprecated_alias_spec.rb
index 9ddd87a783c..481e387ba03 100644
--- a/logstash-core/spec/logstash/settings/setting_with_deprecated_alias_spec.rb
+++ b/logstash-core/spec/logstash/settings/setting_with_deprecated_alias_spec.rb
@@ -52,6 +52,13 @@
     end
 
     include_examples '#validate_value success'
+
+    context "#observe_post_process" do
+      it 'does not emit a deprecation warning' do
+        expect(LogStash::Settings.deprecation_logger).to_not receive(:deprecated).with(a_string_including(deprecated_setting_name))
+        settings.get_setting(deprecated_setting_name).observe_post_process
+      end
+    end
   end
 
   context "when only the deprecated alias is set" do
@@ -71,6 +78,13 @@
 
     include_examples '#validate_value success'
 
+    context "#observe_post_process" do
+      it 're-emits the deprecation warning' do
+        expect(LogStash::Settings.deprecation_logger).to receive(:deprecated).with(a_string_including(deprecated_setting_name))
+        settings.get_setting(deprecated_setting_name).observe_post_process
+      end
+    end
+
     it 'validates deprecated alias' do
       expect { settings.get_setting(canonical_setting_name).deprecated_alias.validate_value }.to_not raise_error
     end
@@ -107,6 +121,13 @@
     end
 
     include_examples '#validate_value success'
+
+    context "#observe_post_process" do
+      it 'does not emit a deprecation warning' do
+        expect(LogStash::Settings.deprecation_logger).to_not receive(:deprecated).with(a_string_including(deprecated_setting_name))
+        settings.get_setting(deprecated_setting_name).observe_post_process
+      end
+    end
   end
 
   context "when both the canonical setting and deprecated alias are set" do
diff --git a/logstash-core/spec/logstash/settings_spec.rb b/logstash-core/spec/logstash/settings_spec.rb
index 241ac2272eb..3e0b425dd46 100644
--- a/logstash-core/spec/logstash/settings_spec.rb
+++ b/logstash-core/spec/logstash/settings_spec.rb
@@ -144,6 +144,18 @@
     it "should preserve original settings" do
       expect(settings.get("foo")).to eq("bar")
     end
+
+    context 'when a registered setting responds to `observe_post_process`' do
+      let(:observe_post_process_setting) do
+        LogStash::Setting::Boolean.new("this.that", true).tap { |s| allow(s).to receive(:observe_post_process) }
+      end
+      subject(:settings) do
+        described_class.new.tap { |s| s.register(observe_post_process_setting) }
+      end
+      it 'it sends `observe_post_process`' do
+        expect(observe_post_process_setting).to have_received(:observe_post_process)
+      end
+    end
   end
 
   context "transient settings" do