class ActiveSupport::BacktraceCleaner

Backtrace Cleaner¶ ↑

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 = ActiveSupport::BacktraceCleaner.new
root = "#{Rails.root}/"
bc.add_filter   { |line| line.delete_prefix(root) } # strip the Rails.root prefix
bc.add_silencer { |line| /puma|rubygems/.match?(line) } # 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

Public Class Methods

new ()

# File activesupport/lib/active_support/backtrace_cleaner.rb, line 35
def initialize
  @filters, @silencers = [], []
  add_core_silencer
  add_gem_filter
  add_gem_silencer
  add_stdlib_silencer
end

Public Instance 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"
root = "#{Rails.root}/"
backtrace_cleaner.add_filter { |line| line.delete_prefix(root) }

# File activesupport/lib/active_support/backtrace_cleaner.rb, line 154
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 "puma", like "/gems/puma/server.rb" or "/app/my_puma_server/rb"
backtrace_cleaner.add_silencer { |line| /puma/.match?(line) }

# File activesupport/lib/active_support/backtrace_cleaner.rb, line 163
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.

# File activesupport/lib/active_support/backtrace_cleaner.rb, line 45
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

clean_frame (frame, kind = :silent)

Returns the frame with all filters applied. returns nil if the frame was silenced.

# File activesupport/lib/active_support/backtrace_cleaner.rb, line 73
def clean_frame(frame, kind = :silent)
  frame = frame.to_s
  @filters.each do |f|
    frame = f.call(frame.to_s)
  end

  case kind
  when :silent
    frame unless @silencers.any? { |s| s.call(frame) }
  when :noise
    frame if @silencers.any? { |s| s.call(frame) }
  else
    frame
  end
end

clean_locations (locations, kind = :silent)

Given an array of Thread::Backtrace::Location objects, returns an array with the clean ones:

clean_locations = backtrace_cleaner.clean_locations(caller_locations)

Filters and silencers receive strings as usual. However, the path attributes of the locations in the returned array are the original, unfiltered ones, since locations are immutable.

# File activesupport/lib/active_support/backtrace_cleaner.rb, line 67
def clean_locations(locations, kind = :silent)
  locations.select { |location| clean_frame(location, kind) }
end

filter (backtrace, kind = :silent)

Alias for: clean

first_clean_frame (kind = :silent)

Returns the first clean frame of the caller’s backtrace, or nil.

Frames are strings.

# File activesupport/lib/active_support/backtrace_cleaner.rb, line 94
def first_clean_frame(kind = :silent)
  caller_location_skipped = false

  Thread.each_caller_location do |location|
    unless caller_location_skipped
      caller_location_skipped = true
      next
    end

    frame = clean_frame(location, kind)
    return frame if frame
  end
end

first_clean_location (kind = :silent)

Returns the first clean location of the caller’s call stack, or nil.

Locations are Thread::Backtrace::Location objects. Since they are immutable, their path attributes are the original ones, but filters are applied internally so silencers can still rely on them.

# File activesupport/lib/active_support/backtrace_cleaner.rb, line 113
def first_clean_location(kind = :silent)
  caller_location_skipped = false

  Thread.each_caller_location do |location|
    unless caller_location_skipped
      caller_location_skipped = true
      next
    end

    return location if clean_frame(location, kind)
  end
end

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 177
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 170
def remove_silencers!
  @silencers = []
end