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.
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Constants
FORMATTED_GEMS_PATTERN | = | /\A[^\/]+ \([\w.]+\) / |
Class Public methods
new() Link
Instance Public methods
add_filter(&block) Link
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) }
add_silencer(&block) Link
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) }
clean(backtrace, kind = :silent) Link
Returns the backtrace after all filters and silencers have been run against it. Filters run first, then silencers.
clean_frame(frame, kind = :silent) Link
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) Link
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.
first_clean_frame(kind = :silent) Link
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) Link
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!() Link
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.
remove_silencers!() Link
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.