Better error reporting

[apohllo]

Describe the bug

The error reporting when a function is wrongly composed is not useful.

To Reproduce

Let's take the example from the documentation

require 'dry/transformer'

class Mapper < Dry::Transformer::Pipe
  import Dry::Transformer::ArrayTransformations
  import Dry::Transformer::HashTransformations

  define! do
    map_array do
      symbolize_keys
      rename_keys :user_name, :name # the error is here!
      nest :address, [:city, :street, :zipcode]
    end
  end
end


mapper = Mapper.new

pp mapper.(
  [
    { 'user_name' => 'Jane',
      'city' => 'NYC',
      'street' => 'Street 1',
      'zipcode' => '123'
    }
  ]
)

Running the code gives:

Traceback (most recent call last):
	11: from example.rb:19:in `<main>'
	10: from /home/apohllo/.rvm/gems/ruby-2.7.2/gems/dry-transformer-0.1.1/lib/dry/transformer/pipe.rb:71:in `call'
	 9: from /home/apohllo/.rvm/gems/ruby-2.7.2/gems/dry-transformer-0.1.1/lib/dry/transformer/function.rb:50:in `call'
	 8: from /home/apohllo/.rvm/gems/ruby-2.7.2/gems/dry-transformer-0.1.1/lib/dry/transformer/function.rb:50:in `call'
	 7: from /home/apohllo/.rvm/gems/ruby-2.7.2/gems/dry-transformer-0.1.1/lib/dry/transformer/array.rb:45:in `map_array'
	 6: from /home/apohllo/.rvm/gems/ruby-2.7.2/gems/dry-transformer-0.1.1/lib/dry/transformer/array.rb:45:in `map'
	 5: from /home/apohllo/.rvm/gems/ruby-2.7.2/gems/dry-transformer-0.1.1/lib/dry/transformer/array.rb:45:in `block in map_array'
	 4: from /home/apohllo/.rvm/gems/ruby-2.7.2/gems/dry-transformer-0.1.1/lib/dry/transformer/composite.rb:33:in `call'
	 3: from /home/apohllo/.rvm/gems/ruby-2.7.2/gems/dry-transformer-0.1.1/lib/dry/transformer/composite.rb:33:in `call'
	 2: from /home/apohllo/.rvm/gems/ruby-2.7.2/gems/dry-transformer-0.1.1/lib/dry/transformer/function.rb:50:in `call'
	 1: from /home/apohllo/.rvm/gems/ruby-2.7.2/gems/dry-transformer-0.1.1/lib/dry/transformer/function.rb:50:in `call'
/home/apohllo/.rvm/gems/ruby-2.7.2/gems/dry-transformer-0.1.1/lib/dry/transformer/hash.rb:170:in `rename_keys': wrong number of arguments (given 3, expected 2) (ArgumentError)

Expected behavior

I would like that the stack trace included the line that introduced the error, i.e. the line with the comment. But there is no reference to that line, making debugging of the composed code pretty hard. This stays in contrast with regular ruby code, which would directly indicate the line that has the error.

[solnic]

Thanks! I'll make sure this is addressed for the 1.0.0 release.