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

defextract_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).

classDummydeftest(_dummy_arg)node=RubyVM::AbstractSyntaxTree.of(caller_locations.first,keep_script_lines: true)ErrorHighlight.spot(node)endendppDummy.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.newdefformatter.message_for(spot)marker=" " * spot[:first_column] + "^" + "~" * (spot[:last_column] - spot[:first_column] - 1)"\n\n#{spot[:snippet]}#{marker}"endErrorHighlight.formatter=formatter1.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.