Rails backtrace silencers do not work, while filters do

Question

Fresh Rails 4.2 set up. I want to suppress long error backtraces. In the following backtrace log first line would be enough for me, and next 4 could be removed

Answer 1

This is because of https://github.com/vipulnsward/rails/blob/ecc8f283cfc1b002b5141c527a827e74b770f2f0/actionpack/lib/action_dispatch/middleware/debug_exceptions.rb#L155-L156

Since application_trace is empty(This is because error is not from user code but route error), we are falling back to framework_trace, which does not filter it (it filters only noise).

You can reach your gaol it with creating your own log_formatter. In your development.rb and/or test.rb add

config.log_formatter = SilentLogger.new
config.log_formatter.add_silencer { |line| line =~ /lib/ }

And create simple class in models with only method call required. There you can modify your backtrace as you wish.

class SilentLogger
  def initialize
    @silencers = []
  end

  def add_silencer(&block)
    @silencers << block
  end

  def call(severity, timestamp, progname, msg)
    backtrace = (String === msg) ? "#{msg}\n" : "#{msg.inspect}\n"

    return backtrace if @silencers.empty?

    @silencers.each do |s|
      backtrace = backtrace.split("\n").delete_if { |line| s.call(line) }
    end

    backtrace.join("\n")
  end
end