st0012/power_trace

Buff exception backtrace with local variables, passed in arguments and instance variables!

power_trace

Backtrace (Stack traces) are essential information for debugging our applications. However, they only tell us what the program did, but don't tell us what it had (the arguments, local variables...etc.). So it's very often that we'd need to visit each call site, rerun the program, and try to print out the variables. To me, It's like the Google map's navigation only tells us the name of the roads, but not showing us the map along with them.

So I hope to solve this problem by adding some additional runtime info to the backtrace, and save us the work to manually look them up.

Please Don't Use It On Production

Installation

Add this line to your application's Gemfile:

gem 'power_trace', group: [:test, :development]

And then execute:

$ bundle install

Or install it yourself as:

$ gem install power_trace

Usage

Use It With Rails

You can add more context to Rails' exception reporting with:

# config/initializers/power_trace.rb

if defined?(PowerTrace)
  PowerTrace.integrations = :rails
end

Result:

Before

After

Use It With RSpec

You can prettify RSpec's error messages with power_trace by adding:

# spec/spec_helper.rb

require "power_trace"
PowerTrace.integrations = :rspec

Result:

Before

After

Use It With Minitest

You can also prettify Minitest's error messages with power_trace with:

# test/test_helper.rb

require "power_trace"
PowerTrace.integrations = :minitest

Result:

Before

After

Use It With Multiple Integrations

It's also possible to use it with multiple integrations (e.g. rspec + rails):

PowerTrace.integrations = [:rspec, :rails]

Call power_trace directly

If you call power_trace directly, it'll return a PowerTrace::Stack instance that contains all the processed traces. You can then use it in 3 different ways:

• Print it directly
• Access each trace (Entry instance)
• Convert it into backtraces (an array of strings)

Print It Directly

You can use puts(power_trace) to print the beautiful output to stdout:

It should look just like the normal puts(caller), just colorized and with more helpful info.

Access Individual Entries

Except for the call site, each entry also contains rich information about the runtime context. You can build your own debugging tool with that information easily.

Every entry has these attributes:

• filepath
• line_number
• receiver - the receiver object
• frame - the call frame (Binding) object
• locals - local variables in that frame
• arguments
  • the method call's arguments
  • will be empty for block entries

Convert It Into Backtraces

You can do it by calling power_trace.to_backtrace. The major usage is to replace an exception object's backtrace like

a_exception.set_backtrace(power_trace.to_backtrace)

I don't recommend using it like this for other purposes, though. Because by default, all entries will be color-encoded strings. Also, the embedded arguments/locals aren't easily parseable. For other uses, you should either print it directly or process the traces without calling to_backtrace.

Options

• colorize - to decide whether to colorize each entry in their string format. Default is true.
• line_limit - power_trace truncates every argument/local variable's value to avoid creating too much noise. Default is 100
• extra_info_indent -

By default, extra info sections (locals/arguments) are indented with 4 spaces. Like:

/Users/st0012/projects/power_trace/spec/fixtures.rb:23:in `forth_call'
    (Arguments)
      num1: 20
      num2: 10

You can change this indentation with the extra_info_indent: Int option. It's useful when you need to adjust the output from some formatting tools (like RSpec formatters).

Use It With StandardError (Experimental)

If you set

PowerTrace.replace_backtrace = true

it will replace every StandardError exception's backtrace with the power_trace.to_backtrace. So most of the error traces you see will also contain the colorized environment information!

This is still an experimental feature for now, as it has a very wide impact on all the libraries and your own code. Don't try this on production!!!!

Get power_trace Manually From A StandardError Exception

If you think the above feature is too aggressive. You can access an exception object's enhanced backtrace manually with the power_trace method:

begin
  perform_a_call
rescue => e
  e.stored_power_trace # <= like this
end

This feature doesn't require any flag to enable, as the information is added as an extra field and doesn't override anything.

Inspirations & Helpful Tools

• pretty_backtrace
• pry-stack_explorer
• tapping_device

Development

After checking out the repo, run bin/setup to install dependencies. Then, run rake spec to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and tags, and push the .gem file to rubygems.org.

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/st0012/power_trace. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the code of conduct.

License

The gem is available as open source under the terms of the MIT License.

Code of Conduct

Everyone interacting in the PowerTrace project's codebases, issue trackers, chat rooms and mailing lists is expected to follow the code of conduct.