Allow entirely opting out of deprecation warnings

Previously if you did `app.config.active_support.deprecation = :silence`, some work would still be done on each call to `ActiveSupport::Deprecation.warn`. Specifically [checking the backtrace](12372c5482/activesupport/lib/active_support/deprecation/reporting.rb (L21)), generating the [deprecation warning](12372c5482/activesupport/lib/active_support/deprecation/reporting.rb (L22)), and [checking if the warning is disallowed](12372c5482/activesupport/lib/active_support/deprecation/reporting.rb (L23)).

In very hot paths, this could cause performance issues. This PR lets you turn off deprecation reporting entirely for a specific environment.

```ruby
config.active_support.report_deprecations = false
```

^ so has the same outcome as:

```ruby
config.active_support.deprecation = :silence
config.active_support.disallowed_deprecation = :silence
```

But it will short circuit [here](12372c5482/activesupport/lib/active_support/deprecation/reporting.rb (L19)).

activesupport/CHANGELOG.md

@@ -1,3 +1,26 @@
+*   Allow entirely opting out of deprecation warnings
+
+    Previously if you did `app.config.active_support.deprecation = :silence`, some work would
+    still be done on each call to `ActiveSupport::Deprecation.warn`. In very hot paths, this could
+    cause performance issues.
+
+    Now, you can make `ActiveSupport::Deprecation.warn` a no-op:
+
+    ```ruby
+    config.active_support.report_deprecations = false
+    ```
+
+    This is the default in production for new apps. It is the equivalent to:
+
+    ```ruby
+    config.active_support.deprecation = :silence
+    config.active_support.disallowed_deprecation = :silence
+    ```
+
+    but will take a more optimised code path.
+
+    *Alex Ghiculescu*
+
 *   Faster tests by parallelizing only when overhead is justified by the number
     of them.
 

activesupport/lib/active_support/deprecation/behaviors.rb

@@ -54,7 +54,7 @@ module ActiveSupport
     # [+stderr+]  Log all deprecation warnings to <tt>$stderr</tt>.
     # [+log+]     Log all deprecation warnings to +Rails.logger+.
     # [+notify+]  Use +ActiveSupport::Notifications+ to notify +deprecation.rails+.
-    # [+silence+] Do nothing.
+    # [+silence+] Do nothing. On Rails, set `config.active_support.report_deprecations = false` to disable all behaviors.
     #
     # Setting behaviors only affects deprecations that happen after boot time.
     # For more information you can read the documentation of the +behavior=+ method.
@@ -93,6 +93,9 @@ module ActiveSupport
       #   ActiveSupport::Deprecation.behavior = ->(message, callstack, deprecation_horizon, gem_name) {
       #     # custom stuff
       #   }
+      #
+      # If you are using Rails, you can set `config.active_support.report_deprecations = false` to disable
+      # all deprecation behaviors. This is similar to the `silence` option but more performant.
       def behavior=(behavior)
         @behavior = Array(behavior).map { |b| DEFAULT_BEHAVIORS[b] || arity_coerce(b) }
       end

activesupport/lib/active_support/railtie.rb

@@ -39,16 +39,22 @@ module ActiveSupport
     end
 
     initializer "active_support.deprecation_behavior" do |app|
-      if deprecation = app.config.active_support.deprecation
-        ActiveSupport::Deprecation.behavior = deprecation
-      end
+      if app.config.active_support.report_deprecations == false
+        ActiveSupport::Deprecation.silenced = true
+        ActiveSupport::Deprecation.behavior = :silence
+        ActiveSupport::Deprecation.disallowed_behavior = :silence
+      else
+        if deprecation = app.config.active_support.deprecation
+          ActiveSupport::Deprecation.behavior = deprecation
+        end
 
-      if disallowed_deprecation = app.config.active_support.disallowed_deprecation
-        ActiveSupport::Deprecation.disallowed_behavior = disallowed_deprecation
-      end
+        if disallowed_deprecation = app.config.active_support.disallowed_deprecation
+          ActiveSupport::Deprecation.disallowed_behavior = disallowed_deprecation
+        end
 
-      if disallowed_warnings = app.config.active_support.disallowed_deprecation_warnings
-        ActiveSupport::Deprecation.disallowed_warnings = disallowed_warnings
+        if disallowed_warnings = app.config.active_support.disallowed_deprecation_warnings
+          ActiveSupport::Deprecation.disallowed_warnings = disallowed_warnings
+        end
       end
     end
 

activesupport/test/deprecation_test.rb

@@ -298,8 +298,12 @@ class DeprecationTest < ActiveSupport::TestCase
     end
 
     ActiveSupport::Deprecation.silenced = true
+    assert ActiveSupport::Deprecation.silenced
+
     assert_not_deprecated { @dtc.partially }
+
     ActiveSupport::Deprecation.silenced = false
+    assert_not ActiveSupport::Deprecation.silenced
   end
 
   def test_silence_threaded

guides/source/configuring.md

@@ -922,20 +922,18 @@ There are a few configuration options available in Active Support:
 
 * `config.active_support.cache_format_version` specifies which version of the cache serializer to use. Possible values are `6.1` and `7.0`.
 
+* `config.active_support.deprecation` configures the behavior of deprecation warnings. The options are `:raise`, `:stderr`, `:log`, `:notify`, or `:silence`. The default is `:stderr`. Alternatively, you can set `ActiveSupport::Deprecation.behavior`.
+
+* `config.active_support.disallowed_deprecation` configures the behavior of disallowed deprecation warnings. The options are `:raise`, `:stderr`, `:log`, `:notify`, or `:silence`. The default is `:raise`. Alternatively, you can set `ActiveSupport::Deprecation.disallowed_behavior`.
+
+* `config.active_support.disallowed_deprecation_warnings` configures deprecation warnings that the Application considers disallowed. This allows, for example, specific deprecations to be treated as hard failures. Alternatively, you can set `ActiveSupport::Deprecation.disallowed_warnings`.
+
+* `config.active_support.report_deprecations` allows you to disable all deprecation warnings (including disallowed deprecations); it makes `ActiveSupport::Deprecation.warn` a no-op. This is enabled by default in production.
+
 * `ActiveSupport::Logger.silencer` is set to `false` to disable the ability to silence logging in a block. The default is `true`.
 
 * `ActiveSupport::Cache::Store.logger` specifies the logger to use within cache store operations.
 
-* `ActiveSupport::Deprecation.behavior` alternative setter to `config.active_support.deprecation` which configures the behavior of deprecation warnings for Rails.
-
-* `ActiveSupport::Deprecation.disallowed_behavior` alternative setter to `config.active_support.disallowed_deprecation` which configures the behavior of disallowed deprecation warnings for Rails.
-
-* `ActiveSupport::Deprecation.disallowed_warnings` alternative setter to `config.active_support.disallowed_deprecation_warnings` which configures deprecation warnings that the Application considers disallowed. This allows, for example, specific deprecations to be treated as hard failures.
-
-* `ActiveSupport::Deprecation.silence` takes a block in which all deprecation warnings are silenced.
-
-* `ActiveSupport::Deprecation.silenced` sets whether or not to display deprecation warnings. The default is `false`.
-
 * `ActiveSupport.utc_to_local_returns_utc_offset_times` configures
   `ActiveSupport::TimeZone.utc_to_local` to return a time with a UTC offset
   instead of a UTC time incorporating that offset.
@@ -1673,7 +1671,7 @@ Below is a comprehensive list of all the initializers found in Rails in the orde
 
 * `i18n.callbacks`: In the development environment, sets up a `to_prepare` callback which will call `I18n.reload!` if any of the locales have changed since the last request. In production this callback will only run on the first request.
 
-* `active_support.deprecation_behavior`: Sets up deprecation reporting for environments, defaulting to `:log` for development, `:notify` for production, and `:stderr` for test. If a value isn't set for `config.active_support.deprecation` then this initializer will prompt the user to configure this line in the current environment's `config/environments` file. Can be set to an array of values. This initializer also sets up behaviors for disallowed deprecations, defaulting to `:raise` for development and test and `:log` for production. Disallowed deprecation warnings default to an empty array.
+* `active_support.deprecation_behavior`: Sets up deprecation reporting for environments, defaulting to `:log` for development, `:silence` for production, and `:stderr` for test.  Can be set to an array of values. This initializer also sets up behaviors for disallowed deprecations, defaulting to `:raise` for development and test and `:silence` for production. Disallowed deprecation warnings default to an empty array.
 
 * `active_support.initialize_time_zone`: Sets the default time zone for the application based on the `config.time_zone` setting, which defaults to "UTC".
 

railties/lib/rails/generators/rails/app/templates/config/environments/production.rb.tt

@@ -84,14 +84,8 @@ Rails.application.configure do
   # the I18n.default_locale when a translation cannot be found).
   config.i18n.fallbacks = true
 
-  # Send deprecation notices to registered listeners.
-  config.active_support.deprecation = :notify
-
-  # Log disallowed deprecations.
-  config.active_support.disallowed_deprecation = :log
-
-  # Tell Active Support which deprecation messages to disallow.
-  config.active_support.disallowed_deprecation_warnings = []
+  # Don't log any deprecations.
+  config.active_support.report_deprecations = false
 
   # Use default logging formatter so that PID and timestamp are not suppressed.
   config.log_formatter = ::Logger::Formatter.new

railties/test/application/configuration_test.rb

@@ -3459,6 +3459,16 @@ module ApplicationTests
       assert_equal true, ActiveSupport::TimeWithZone.methods(false).include?(:name)
     end
 
+    test "can entirely opt out of ActiveSupport::Deprecations" do
+      add_to_config "config.active_support.report_deprecations = false"
+
+      app "production"
+
+      assert_equal true, ActiveSupport::Deprecation.silenced
+      assert_equal [ActiveSupport::Deprecation::DEFAULT_BEHAVIORS[:silence]], ActiveSupport::Deprecation.behavior
+      assert_equal [ActiveSupport::Deprecation::DEFAULT_BEHAVIORS[:silence]], ActiveSupport::Deprecation.disallowed_behavior
+    end
+
     private
       def set_custom_config(contents, config_source = "custom".inspect)
         app_file "config/custom.yml", contents