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module ActiveSupport
# 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 <tt>BacktraceCleaner#remove_silencers!</tt>, 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.
class BacktraceCleaner
def initialize
@filters, @silencers = [], []
end
# Returns the backtrace after all filters and silencers have been run against it. Filters run first, then silencers.
def clean(backtrace, kind = :silent)
filtered = filter(backtrace)
case kind
when :silent
silence(filtered)
when :noise
noise(filtered)
else
filtered
end
end
# 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, '') }
def add_filter(&block)
@filters << block
end
# 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/ }
def add_silencer(&block)
@silencers << block
end
# 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.
def remove_silencers!
@silencers = []
end
def remove_filters!
@filters = []
end
private
def filter(backtrace)
@filters.each do |f|
backtrace = backtrace.map { |line| f.call(line) }
end
backtrace
end
def silence(backtrace)
@silencers.each do |s|
backtrace = backtrace.reject { |line| s.call(line) }
end
backtrace
end
def noise(backtrace)
@silencers.each do |s|
backtrace = backtrace.select { |line| s.call(line) }
end
backtrace
end
end
end
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