Prepend specified path to backtrace in rspec output (for rails in subdirectory).

backtrace_relative_path.rb

# NOTE: Put this file to spec/support/ .

# Prepend specified path to backtrace and Failure/Error section.
# Useful for multi module repository where rails is placed in the subdirectory.
# Intended for editors with click-to-open-file feature.
#
# For example
#   # ./spec/models/your_model_spec.rb:12:in `your_method'
# to
#   # ./rails/spec/models/your_model_spec.rb:12:in `your_method'

if ENV['RSPEC_RELATIVE_ROOT']
  RSpec.configure do |config|
    # https://github.com/rspec/rspec-core/blob/7b6b9c3f2e2878213f97d6fc9e9eb23c323cfe1c/lib/rspec/core/backtrace_formatter.rb#L49
    orig_backtrace_line = config.backtrace_formatter.method(:backtrace_line)
    config.backtrace_formatter.define_singleton_method(:backtrace_line) do |*args|
      orig_backtrace_line.call(*args)&.sub(%r{^\./}, "./#{ENV['RSPEC_RELATIVE_ROOT']}/")
    end
  end

  # https://github.com/rspec/rspec-core/blob/7b6b9c3f2e2878213f97d6fc9e9eb23c323cfe1c/lib/rspec/core/example.rb#L96
  RSpec::Core::Example.class_eval do
    alias_method :location_rerun_argument_without_relative_root, :location_rerun_argument
    def location_rerun_argument
      location_rerun_argument_without_relative_root&.sub(%r{^\./}, "./#{ENV['RSPEC_RELATIVE_ROOT']}/")
    end
  end
end