0.06
There's a lot of open issues
The gem enhances Exception#message by adding a short explanation where the exception is raised
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
2021
2022
 Dependencies
 Project Readme

ErrorHighlight

Installation

Ruby 3.1 will ship with this gem and it will automatically be required when a Ruby process starts up. No special setup is required.

Note: This gem works only on MRI and requires Ruby 3.1 or later because it depends on MRI's internal APIs that are available since 3.1.

Examples

1.time {}
$ ruby test.rb
test.rb:1:in `<main>': undefined method `time' for 1:Integer (NoMethodError)

1.time {}
 ^^^^^
Did you mean?  times

More example

def extract_value(data)
  data[:results].first[:value]
end

When data is { :results => [] }, the following error message is shown:

$ ruby test.rb
test.rb:2:in `extract_value': undefined method `[]' for nil:NilClass (NoMethodError)

  data[:results].first[:value]
                      ^^^^^^^^
        from test.rb:5:in `<main>'

When data is nil, it prints:

$ ruby test.rb
test.rb:2:in `extract_value': undefined method `[]' for nil:NilClass (NoMethodError)

  data[:results].first[:value]
      ^^^^^^^^^^
        from test.rb:5:in `<main>'

Using the ErrorHighlight.spot

Note: This API is experimental, may change in future.

You can use the ErrorHighlight.spot method to get the snippet data. Note that the argument must be a RubyVM::AbstractSyntaxTree::Node object that is created with keep_script_lines: true option (which is available since Ruby 3.1).

class Dummy
  def test(_dummy_arg)
    node = RubyVM::AbstractSyntaxTree.of(caller_locations.first, keep_script_lines: true)
    ErrorHighlight.spot(node)
  end
end

pp Dummy.new.test(42) # <- Line 8
#           ^^^^^       <- Column 12--17

#=> {:first_lineno=>8,
#    :first_column=>12,
#    :last_lineno=>8,
#    :last_column=>17,
#    :snippet=>"pp Dummy.new.test(42) # <- Line 8\n"}

Custom Formatter

If you want to customize the message format for code snippet, use ErrorHighlight.formatter= to set your custom object that responds to message_for method.

formatter = Object.new
def formatter.message_for(spot)
  marker = " " * spot[:first_column] + "^" + "~" * (spot[:last_column] - spot[:first_column] - 1)

  "\n\n#{ spot[:snippet] }#{ marker }"
end

ErrorHighlight.formatter = formatter

1.time {}

#=>
#
# test.rb:10:in `<main>': undefined method `time' for 1:Integer (NoMethodError)
#
# 1.time {}
#  ^~~~~
# Did you mean?  times

Disabling error_highlight

Occasionally, you may want to disable the error_highlight gem for e.g. debugging issues in the error object itself. You can disable it entirely by specifying --disable-error_highlight option to the ruby command:

$ ruby --disable-error_highlight -e '1.time {}'
-e:1:in `<main>': undefined method `time' for 1:Integer (NoMethodError)
Did you mean?  times

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/ruby/error_highlight.

License

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