Debugging Ruby and Ruby on Rails Cheatsheet

Basic

puts

You can put puts or if it doesn't work, Rails.logger, almost everywhere (except some very weird DSL gems) - controllers, views (<% puts "blabla" %>), jobs.

binding.pry

The same, stops execution and provides command line. Pain to use to debug controllers in Docker, but still useful for tests.

More Advanced

caller

In a prompt or anywhere in a method add caller and it provides backtrace as an array.

irb(main):003> caller
=>
["/home/damon/.rbenv/versions/3.2.2/lib/ruby/gems/3.2.0/gems/irb-1.12.0/lib/irb/workspace.rb:117:in `eval'",
 "/home/damon/.rbenv/versions/3.2.2/lib/ruby/gems/3.2.0/gems/irb-1.12.0/lib/irb/workspace.rb:117:in `evaluate'",
 "/home/damon/.rbenv/versions/3.2.2/lib/ruby/gems/3.2.0/gems/irb-1.12.0/lib/irb/context.rb:609:in `evaluate'",
 "/home/damon/.rbenv/versions/3.2.2/lib/ruby/gems/3.2.0/gems/irb-1.12.0/lib/irb.rb:1012:in `block (2 levels) in eval_input'",
 "/home/damon/.rbenv/versions/3.2.2/lib/ruby/gems/3.2.0/gems/irb-1.12.0/lib/irb.rb:1323:in `signal_status'",
 "/home/damon/.rbenv/versions/3.2.2/lib/ruby/gems/3.2.0/gems/irb-1.12.0/lib/irb.rb:1005:in `block in eval_input'",
 "/home/damon/.rbenv/versions/3.2.2/lib/ruby/gems/3.2.0/gems/irb-1.12.0/lib/irb.rb:1085:in `block in each_top_level_statement'",
 "/home/damon/.rbenv/versions/3.2.2/lib/ruby/gems/3.2.0/gems/irb-1.12.0/lib/irb.rb:1082:in `loop'",
 "/home/damon/.rbenv/versions/3.2.2/lib/ruby/gems/3.2.0/gems/irb-1.12.0/lib/irb.rb:1082:in `each_top_level_statement'",
 "/home/damon/.rbenv/versions/3.2.2/lib/ruby/gems/3.2.0/gems/irb-1.12.0/lib/irb.rb:1004:in `eval_input'",
 "/home/damon/.rbenv/versions/3.2.2/lib/ruby/gems/3.2.0/gems/irb-1.12.0/lib/irb.rb:988:in `block in run'",
 "/home/damon/.rbenv/versions/3.2.2/lib/ruby/gems/3.2.0/gems/irb-1.12.0/lib/irb.rb:987:in `catch'",
 "/home/damon/.rbenv/versions/3.2.2/lib/ruby/gems/3.2.0/gems/irb-1.12.0/lib/irb.rb:987:in `run'",
 "/home/damon/.rbenv/versions/3.2.2/lib/ruby/gems/3.2.0/gems/irb-1.12.0/lib/irb.rb:884:in `start'",
 "/home/damon/.rbenv/versions/3.2.2/lib/ruby/gems/3.2.0/gems/railties-7.1.3.2/lib/rails/commands/console/console_command.rb:78:in `start'",
 "/home/damon/.rbenv/versions/3.2.2/lib/ruby/gems/3.2.0/gems/railties-7.1.3.2/lib/rails/commands/console/console_command.rb:16:in `start'",
 "/home/damon/.rbenv/versions/3.2.2/lib/ruby/gems/3.2.0/gems/railties-7.1.3.2/lib/rails/commands/console/console_command.rb:106:in `perform'",
 "/home/damon/.rbenv/versions/3.2.2/lib/ruby/gems/3.2.0/gems/thor-1.3.1/lib/thor/command.rb:28:in `run'",
 "/home/damon/.rbenv/versions/3.2.2/lib/ruby/gems/3.2.0/gems/thor-1.3.1/lib/thor/invocation.rb:127:in `invoke_command'",
 "/home/damon/.rbenv/versions/3.2.2/lib/ruby/gems/3.2.0/gems/railties-7.1.3.2/lib/rails/command/base.rb:178:in `invoke_command'",
 "/home/damon/.rbenv/versions/3.2.2/lib/ruby/gems/3.2.0/gems/thor-1.3.1/lib/thor.rb:527:in `dispatch'",
 "/home/damon/.rbenv/versions/3.2.2/lib/ruby/gems/3.2.0/gems/railties-7.1.3.2/lib/rails/command/base.rb:73:in `perform'",
 "/home/damon/.rbenv/versions/3.2.2/lib/ruby/gems/3.2.0/gems/railties-7.1.3.2/lib/rails/command.rb:71:in `block in invoke'",
 "/home/damon/.rbenv/versions/3.2.2/lib/ruby/gems/3.2.0/gems/railties-7.1.3.2/lib/rails/command.rb:149:in `with_argv'",
 "/home/damon/.rbenv/versions/3.2.2/lib/ruby/gems/3.2.0/gems/railties-7.1.3.2/lib/rails/command.rb:69:in `invoke'",
 "/home/damon/.rbenv/versions/3.2.2/lib/ruby/gems/3.2.0/gems/railties-7.1.3.2/lib/rails/commands.rb:18:in `<top (required)>'",
 "<internal:/home/damon/.rbenv/versions/3.2.2/lib/ruby/3.2.0/rubygems/core_ext/kernel_require.rb>:37:in `require'",
 "<internal:/home/damon/.rbenv/versions/3.2.2/lib/ruby/3.2.0/rubygems/core_ext/kernel_require.rb>:37:in `require'",
 "bin/rails:4:in `<main>'"]

source_location

Find out where the method is defined exactly

OniSorceress::Content::Article.method(:find).source_location
=> ["/home/damon/.rbenv/versions/3.2.2/lib/ruby/gems/3.2.0/gems/activerecord-7.1.3.2/lib/active_record/core.rb", 243]

Returns nil for methods defined in C like String#to_s.

owner of method

Find out which module provides the method

"damon".method(:to_s).owner
=> String