class BacktraceCleaner

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 =~ /puma|rubygems/ } # skip any lines from puma 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.

Constants

FORMATTED_GEMS_PATTERN
VERSION

Public Class Methods

new() click to toggle source

# File lib/backtrace_cleaner.rb, line 39
def initialize
  @filters, @silencers = [], []
  add_gem_filter
  add_gem_silencer
  add_stdlib_silencer
end

Public Instance Methods

add_filter(&block) click to toggle source

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 lib/backtrace_cleaner.rb, line 67
def add_filter(&block)
  @filters << block
end

add_silencer(&block) click to toggle source

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 "puma", like "/gems/puma/server.rb" or "/app/my_puma_server/rb"
backtrace_cleaner.add_silencer { |line| line =~ /puma/ }

# File lib/backtrace_cleaner.rb, line 76
def add_silencer(&block)
  @silencers << block
end

clean(backtrace, kind = :silent) click to toggle source

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

# File lib/backtrace_cleaner.rb, line 48
def clean(backtrace, kind = :silent)
  filtered = filter_backtrace(backtrace)

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

Also aliased as: filter

filter(backtrace, kind = :silent)

Alias for: clean

remove_filters!() click to toggle source

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 lib/backtrace_cleaner.rb, line 90
def remove_filters!
  @filters = []
end

remove_silencers!() click to toggle source

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 lib/backtrace_cleaner.rb, line 83
def remove_silencers!
  @silencers = []
end

Private Instance Methods

add_gem_filter() click to toggle source

# File lib/backtrace_cleaner.rb, line 98
def add_gem_filter
  gems_paths = (Gem.path | [Gem.default_dir]).map { |p| Regexp.escape(p) }
  return if gems_paths.empty?

  gems_regexp = %r{(#{gems_paths.join('|')})/(bundler/)?gems/([^/]+)-([\w.]+)/(.*)}
  gems_result = '\3 (\4) \5'
  add_filter { |line| line.sub(gems_regexp, gems_result) }
end

add_gem_silencer() click to toggle source

# File lib/backtrace_cleaner.rb, line 107
def add_gem_silencer
  add_silencer { |line| FORMATTED_GEMS_PATTERN.match?(line) }
end

add_stdlib_silencer() click to toggle source

# File lib/backtrace_cleaner.rb, line 111
def add_stdlib_silencer
  add_silencer { |line| line.start_with?(RbConfig::CONFIG["rubylibdir"]) }
end

filter_backtrace(backtrace) click to toggle source

# File lib/backtrace_cleaner.rb, line 115
def filter_backtrace(backtrace)
  @filters.each do |f|
    backtrace = backtrace.map { |line| f.call(line) }
  end

  backtrace
end

noise(backtrace) click to toggle source

# File lib/backtrace_cleaner.rb, line 131
def noise(backtrace)
  backtrace - silence(backtrace)
end

silence(backtrace) click to toggle source

# File lib/backtrace_cleaner.rb, line 123
def silence(backtrace)
  @silencers.each do |s|
    backtrace = backtrace.reject { |line| s.call(line) }
  end

  backtrace
end