Class: ActiveSupport::BacktraceCleaner

Inherits:
Object
  • Object
show all
Defined in:
activesupport/lib/active_support/backtrace_cleaner.rb

Overview

Backtraces often include many lines that are not relevant for the context under review. This makes it hard to find the signal amongst the backtrace noise, and adds debugging time. With a BacktraceCleaner, filters and silencers are used to remove the noisy lines, so that only the most relevant lines remain.

Filters are used to modify lines of data, while silencers are used to remove lines entirely. The typical filter use case is to remove lengthy path information from the start of each line, and view file paths relevant to the app directory instead of the file system root. The typical silencer use case is to exclude the output of a noisy library from the backtrace, so that you can focus on the rest.

bc = BacktraceCleaner.new
bc.add_filter   { |line| line.gsub(Rails.root, '') } # strip the Rails.root prefix
bc.add_silencer { |line| line =~ /mongrel|rubygems/ } # skip any lines from mongrel or rubygems
bc.clean(exception.backtrace) # perform the cleanup

To reconfigure an existing BacktraceCleaner (like the default one in Rails) and show as much data as possible, you can always call BacktraceCleaner#remove_silencers!, which will restore the backtrace to a pristine state. If you need to reconfigure an existing BacktraceCleaner so that it does not filter or modify the paths of any lines of the backtrace, you can call BacktraceCleaner#remove_filters! These two methods will give you a completely untouched backtrace.

Inspired by the Quiet Backtrace gem by Thoughtbot.

Direct Known Subclasses

Rails::BacktraceCleaner

Instance Method Summary collapse

Constructor Details

#initializeBacktraceCleaner



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# File 'activesupport/lib/active_support/backtrace_cleaner.rb', line 30

def initialize
  @filters, @silencers = [], []
end

Instance Method Details

#add_filter(&block) ⇒ Object

Adds a filter from the block provided. Each line in the backtrace will be mapped against this filter.

# Will turn "/my/rails/root/app/models/person.rb" into "/app/models/person.rb"
backtrace_cleaner.add_filter { |line| line.gsub(Rails.root, '') }


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# File 'activesupport/lib/active_support/backtrace_cleaner.rb', line 55

def add_filter(&block)
  @filters << block
end

#add_silencer(&block) ⇒ Object

Adds a silencer from the block provided. If the silencer returns true for a given line, it will be excluded from the clean backtrace.

# Will reject all lines that include the word "mongrel", like "/gems/mongrel/server.rb" or "/app/my_mongrel_server/rb"
backtrace_cleaner.add_silencer { |line| line =~ /mongrel/ }


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# File 'activesupport/lib/active_support/backtrace_cleaner.rb', line 64

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

#clean(backtrace, kind = :silent) ⇒ Object Also known as: filter

Returns the backtrace after all filters and silencers have been run against it. Filters run first, then silencers.



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# File 'activesupport/lib/active_support/backtrace_cleaner.rb', line 36

def clean(backtrace, kind = :silent)
  filtered = filter_backtrace(backtrace)

  case kind
  when :silent
    silence(filtered)
  when :noise
    noise(filtered)
  else
    filtered
  end
end

#remove_filters!Object

Removes all filters, but leaves in silencers. Useful if you suddenly need to see entire filepaths in the backtrace that you had already filtered out.



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# File 'activesupport/lib/active_support/backtrace_cleaner.rb', line 78

def remove_filters!
  @filters = []
end

#remove_silencers!Object

Will remove all silencers, but leave in the filters. This is useful if your context of debugging suddenly expands as you suspect a bug in one of the libraries you use.



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# File 'activesupport/lib/active_support/backtrace_cleaner.rb', line 71

def remove_silencers!
  @silencers = []
end