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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.to_s, '') } # 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.

Methods
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Class Public methods
new()
# File activesupport/lib/active_support/backtrace_cleaner.rb, line 30
def initialize
  @filters, @silencers = [], []
end
Instance Public methods
add_filter(&block)

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, '') }
# File activesupport/lib/active_support/backtrace_cleaner.rb, line 55
def add_filter(&block)
  @filters << block
end
add_silencer(&block)

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/ }
# File activesupport/lib/active_support/backtrace_cleaner.rb, line 64
def add_silencer(&block)
  @silencers << block
end
clean(backtrace, kind = :silent)

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

Also aliased as: filter
# 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
filter(backtrace, kind = :silent)
Alias for: clean
remove_filters!()

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

# File activesupport/lib/active_support/backtrace_cleaner.rb, line 78
def remove_filters!
  @filters = []
end
remove_silencers!()

Removes all silencers, but leaves in the filters. Useful if your context of debugging suddenly expands as you suspect a bug in one of the libraries you use.

# File activesupport/lib/active_support/backtrace_cleaner.rb, line 71
def remove_silencers!
  @silencers = []
end