Fixes #3556 - Backtrace lines pollute log.

config/initializers/backtrace_silencers.rb

@@ -3,7 +3,11 @@
 # Be sure to restart your server when you modify this file.
 
 # You can add backtrace silencers for libraries that you're using but don't wish to see in your backtraces.
-# Rails.backtrace_cleaner.add_silencer { |line| line =~ /my_noisy_library/ }
+# Rails.backtrace_cleaner.add_silencer { |line| %r{puma|rubygems}.match?(line) }
 
-# You can also remove all the silencers if you're trying to debug a problem that might stem from framework code.
+# You can add backtrace filters to modify lines of data.
+# Rails.backtrace_cleaner.add_filter { |line| line.gsub(Rails.root.to_s, '') }
+
+# You can also remove all the silencers and filters if you're trying to debug a problem that might stem from framework code.
 # Rails.backtrace_cleaner.remove_silencers!
+# Rails.backtrace_cleaner.remove_filters!

lib/core_ext/logger/formatter.rb

@@ -1,6 +1,7 @@
 # Copyright (C) 2012-2021 Zammad Foundation, http://zammad-foundation.org/
 
 # This customization adds the id of the current Thread to all log lines.
+# The #msg2str method will be extended, so that the "Rails.bracktrace_cleaner" can be used to clean the exceptions.
 # It was introduced to make it more easy to follow the execution of tasks in the log in threaded processes.
 #
 # before:
@@ -18,5 +19,19 @@ class Logger
     def call(severity, time, progname, msg)
       format(FORMAT_WITH_THREAD_ID, severity[0..0], format_datetime(time), Process.pid, Thread.current.object_id, severity, progname, msg2str(msg))
     end
+
+    private
+
+    def msg2str(msg)
+      case msg
+      when ::String
+        msg
+      when ::Exception
+        # "#{ msg.message } (#{ msg.class })\n#{ msg.backtrace.join("\n") if msg.backtrace }"
+        "#{msg.message} (#{msg.class})\n#{Rails.backtrace_cleaner.clean(msg.backtrace).join("\n") if msg.backtrace}"
+      else
+        msg.inspect
+      end
+    end
   end
 end