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.

Example:

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

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.

Instance Method Summary (collapse)

Constructor Details

- (BacktraceCleaner) initialize

Returns a new instance of BacktraceCleaner



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# File 'activesupport/lib/active_support/backtrace_cleaner.rb', line 25

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

Instance Method Details

- (Object) add_filter(&block)

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

Example:

# 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 49

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

- (Object) 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.

Example:

# 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 60

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

- (Object) clean(backtrace, kind = :silent)

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 30

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

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

- (Object) remove_filters!



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# File 'activesupport/lib/active_support/backtrace_cleaner.rb', line 70

def remove_filters!
  @filters = []
end

- (Object) remove_silencers!

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 66

def remove_silencers!
  @silencers = []
end