[close #22917] Don't output to `STDOUT` twice

When `rails console` or `rails server` are used along with a logger set to output to `STDOUT` then the contents will show up twice. This happens because the logger is extended with `ActiveSupportLogger.broadcast` with a destination of STDOUT even if it is already outputting to `STDOUT`.

Previously PR #22592 attempted to fix this issue, but it ended up causing NoMethodErrors. A better approach than relying on adding a method and flow control is to inspect the log destination directly. For this `ActiveSupport::Logger.logger_outputs_to?` was introduced

```ruby
logger = Logger.new(STDOUT)
ActiveSupport::Logger.logger_outputs_to?(logger, STDOUT)
# => true
```

To accomplish this we must look inside of an instance variable of standard lib's Logger `@logdev`. There is a related Ruby proposal to expose this method in a standard way: https://bugs.ruby-lang.org/issues/11955

2 files changed, 21 insertions, 3 deletions

diff --git a/activesupport/lib/active_support/logger.rb b/activesupport/lib/active_support/logger.rb
index 3c9c86c30b..f9aacd20fc 100644
--- a/activesupport/lib/active_support/logger.rb
+++ b/activesupport/lib/active_support/logger.rb
@@ -1,4 +1,3 @@
-require 'active_support/core_ext/module/attribute_accessors'
 require 'active_support/logger_silence'
 require 'logger'
 
@@ -6,6 +5,17 @@ module ActiveSupport
   class Logger < ::Logger
     include LoggerSilence
 
+    # Returns true if the logger destination matches one of the sources
+    #
+    #   logger = Logger.new(STDOUT)
+    #   ActiveSupport::Logger.logger_outputs_to?(logger, STDOUT)
+    #   # => true
+    def self.logger_outputs_to?(logger, *sources)
+      logdev = logger.instance_variable_get("@logdev")
+      logger_source = logdev.dev if logdev.respond_to?(:dev)
+      sources.any? { |source| source == logger_source }
+    end
+
     # Broadcasts logs to multiple loggers.
     def self.broadcast(logger) # :nodoc:
       Module.new do
diff --git a/activesupport/test/logger_test.rb b/activesupport/test/logger_test.rb
index a57dc7a241..317e09b7f2 100644
--- a/activesupport/test/logger_test.rb
+++ b/activesupport/test/logger_test.rb
@@ -17,6 +17,14 @@ class LoggerTest < ActiveSupport::TestCase
     @logger  = Logger.new(@output)
   end
 
+  def test_log_outputs_to
+    assert Logger.logger_outputs_to?(@logger, @output),            "Expected logger_outputs_to? @output to return true but was false"
+    assert Logger.logger_outputs_to?(@logger, @output, STDOUT),    "Expected logger_outputs_to? @output or STDOUT to return true but was false"
+
+    assert_not Logger.logger_outputs_to?(@logger, STDOUT),         "Expected logger_outputs_to? to STDOUT to return false, but was true"
+    assert_not Logger.logger_outputs_to?(@logger, STDOUT, STDERR), "Expected logger_outputs_to? to STDOUT or STDERR to return false, but was true"
+  end
+
   def test_write_binary_data_to_existing_file
     t = Tempfile.new ['development', 'log']
     t.binmode
@@ -65,7 +73,7 @@ class LoggerTest < ActiveSupport::TestCase
   def test_should_not_log_debug_messages_when_log_level_is_info
     @logger.level = Logger::INFO
     @logger.add(Logger::DEBUG, @message)
-    assert ! @output.string.include?(@message)
+    assert_not @output.string.include?(@message)
   end
 
   def test_should_add_message_passed_as_block_when_using_add
@@ -129,7 +137,7 @@ class LoggerTest < ActiveSupport::TestCase
       @logger.error "THIS IS HERE"
     end
 
-    assert !@output.string.include?("NOT THERE")
+    assert_not @output.string.include?("NOT THERE")
     assert @output.string.include?("THIS IS HERE")
   end