cucumber-expressions: index 3 out of matches (IndexError) #329

nwallace · 2018-01-30T15:58:31Z

Summary

Given a certain (slightly complex) regexp to define a step definition, cucumber fails to load and I get an unfriendly error message "index 3 out of matches (IndexError)". The step definition looks like this:

Given /^I am a person( named "(?<first_name>.+) (?<last_name>.+)")?$/ do |first_name, last_name|
  ...
end

Expected Behavior

This step definition worked fine before (known to work against v2.4.0), so it should either work correctly or give me a helpful error message to help me fix the problem.

Current Behavior

An IndexError is raised when cucumber tries to load the step definitions.

$ cucumber
index 3 out of matches (IndexError)
/home/nathan/.gem/ruby/2.5.0/gems/cucumber-expressions-5.0.13/lib/cucumber/cucumber_expressions/group_builder.rb:20:in `offset'
/home/nathan/.gem/ruby/2.5.0/gems/cucumber-expressions-5.0.13/lib/cucumber/cucumber_expressions/group_builder.rb:20:in `build'
/home/nathan/.gem/ruby/2.5.0/gems/cucumber-expressions-5.0.13/lib/cucumber/cucumber_expressions/group_builder.rb:19:in `block in build'
/home/nathan/.gem/ruby/2.5.0/gems/cucumber-expressions-5.0.13/lib/cucumber/cucumber_expressions/group_builder.rb:19:in `map'
/home/nathan/.gem/ruby/2.5.0/gems/cucumber-expressions-5.0.13/lib/cucumber/cucumber_expressions/group_builder.rb:19:in `build'
/home/nathan/.gem/ruby/2.5.0/gems/cucumber-expressions-5.0.13/lib/cucumber/cucumber_expressions/group_builder.rb:19:in `block in build'
/home/nathan/.gem/ruby/2.5.0/gems/cucumber-expressions-5.0.13/lib/cucumber/cucumber_expressions/group_builder.rb:19:in `map'
/home/nathan/.gem/ruby/2.5.0/gems/cucumber-expressions-5.0.13/lib/cucumber/cucumber_expressions/group_builder.rb:19:in `build'
/home/nathan/.gem/ruby/2.5.0/gems/cucumber-expressions-5.0.13/lib/cucumber/cucumber_expressions/tree_regexp.rb:48:in `match'
/home/nathan/.gem/ruby/2.5.0/gems/cucumber-expressions-5.0.13/lib/cucumber/cucumber_expressions/argument.rb:10:in `build'
/home/nathan/.gem/ruby/2.5.0/gems/cucumber-expressions-5.0.13/lib/cucumber/cucumber_expressions/regular_expression.rb:32:in `match'
/home/nathan/.gem/ruby/2.5.0/gems/cucumber-3.1.0/lib/cucumber/glue/step_definition.rb:101:in `arguments_from'
/home/nathan/.gem/ruby/2.5.0/gems/cucumber-3.1.0/lib/cucumber/glue/registry_and_more.rb:66:in `block in step_matches'
/home/nathan/.gem/ruby/2.5.0/gems/cucumber-3.1.0/lib/cucumber/glue/registry_and_more.rb:65:in `each'
/home/nathan/.gem/ruby/2.5.0/gems/cucumber-3.1.0/lib/cucumber/glue/registry_and_more.rb:65:in `reduce'
/home/nathan/.gem/ruby/2.5.0/gems/cucumber-3.1.0/lib/cucumber/glue/registry_and_more.rb:65:in `step_matches'
/home/nathan/.gem/ruby/2.5.0/gems/cucumber-3.1.0/lib/cucumber/step_match_search.rb:19:in `call'
/home/nathan/.gem/ruby/2.5.0/gems/cucumber-3.1.0/lib/cucumber/step_match_search.rb:19:in `call'
/home/nathan/.rubies/ruby-2.5.0/lib/ruby/2.5.0/delegate.rb:83:in `method_missing'
/home/nathan/.gem/ruby/2.5.0/gems/cucumber-3.1.0/lib/cucumber/step_match_search.rb:62:in `call'
/home/nathan/.gem/ruby/2.5.0/gems/cucumber-3.1.0/lib/cucumber/filters/activate_steps.rb:66:in `matches'
/home/nathan/.gem/ruby/2.5.0/gems/cucumber-3.1.0/lib/cucumber/filters/activate_steps.rb:47:in `result'
/home/nathan/.gem/ruby/2.5.0/gems/cucumber-3.1.0/lib/cucumber/filters/activate_steps.rb:37:in `find_match'
/home/nathan/.gem/ruby/2.5.0/gems/cucumber-3.1.0/lib/cucumber/filters/activate_steps.rb:33:in `attempt_to_activate'
/home/nathan/.gem/ruby/2.5.0/gems/cucumber-3.1.0/lib/cucumber/filters/activate_steps.rb:29:in `map'
/home/nathan/.gem/ruby/2.5.0/gems/cucumber-3.1.0/lib/cucumber/filters/activate_steps.rb:29:in `new_test_steps'
/home/nathan/.gem/ruby/2.5.0/gems/cucumber-3.1.0/lib/cucumber/filters/activate_steps.rb:23:in `test_case'
/home/nathan/.gem/ruby/2.5.0/gems/cucumber-3.1.0/lib/cucumber/filters/activate_steps.rb:12:in `test_case'
/home/nathan/.gem/ruby/2.5.0/gems/cucumber-core-3.1.0/lib/cucumber/core/test/case.rb:25:in `describe_to'
/home/nathan/.gem/ruby/2.5.0/gems/cucumber-core-3.1.0/lib/cucumber/core/test/filters/locations_filter.rb:18:in `block in done'
/home/nathan/.gem/ruby/2.5.0/gems/cucumber-core-3.1.0/lib/cucumber/core/test/filters/locations_filter.rb:17:in `each'
/home/nathan/.gem/ruby/2.5.0/gems/cucumber-core-3.1.0/lib/cucumber/core/test/filters/locations_filter.rb:17:in `done'
/home/nathan/.gem/ruby/2.5.0/gems/cucumber-core-3.1.0/lib/cucumber/core/filter.rb:62:in `done'
/home/nathan/.gem/ruby/2.5.0/gems/cucumber-core-3.1.0/lib/cucumber/core/test/filters/tag_filter.rb:18:in `done'
/home/nathan/.gem/ruby/2.5.0/gems/cucumber-core-3.1.0/lib/cucumber/core/compiler.rb:24:in `done'
/home/nathan/.gem/ruby/2.5.0/gems/cucumber-core-3.1.0/lib/cucumber/core/gherkin/parser.rb:37:in `done'
/home/nathan/.gem/ruby/2.5.0/gems/cucumber-core-3.1.0/lib/cucumber/core.rb:32:in `parse'
/home/nathan/.gem/ruby/2.5.0/gems/cucumber-core-3.1.0/lib/cucumber/core.rb:21:in `compile'
/home/nathan/.gem/ruby/2.5.0/gems/cucumber-3.1.0/lib/cucumber/runtime.rb:74:in `run!'
/home/nathan/.gem/ruby/2.5.0/gems/cucumber-3.1.0/lib/cucumber/cli/main.rb:33:in `execute!'
/home/nathan/.gem/ruby/2.5.0/gems/cucumber-3.1.0/bin/cucumber:9:in `<top (required)>'
/home/nathan/.gem/ruby/2.5.0/bin/cucumber:23:in `load'
/home/nathan/.gem/ruby/2.5.0/bin/cucumber:23:in `<top (required)>'
/home/nathan/.gem/ruby/2.5.0/gems/bundler-1.16.1/lib/bundler/cli/exec.rb:75:in `load'
/home/nathan/.gem/ruby/2.5.0/gems/bundler-1.16.1/lib/bundler/cli/exec.rb:75:in `kernel_load'
/home/nathan/.gem/ruby/2.5.0/gems/bundler-1.16.1/lib/bundler/cli/exec.rb:28:in `run'
/home/nathan/.gem/ruby/2.5.0/gems/bundler-1.16.1/lib/bundler/cli.rb:424:in `exec'
/home/nathan/.gem/ruby/2.5.0/gems/bundler-1.16.1/lib/bundler/vendor/thor/lib/thor/command.rb:27:in `run'
/home/nathan/.gem/ruby/2.5.0/gems/bundler-1.16.1/lib/bundler/vendor/thor/lib/thor/invocation.rb:126:in `invoke_command'
/home/nathan/.gem/ruby/2.5.0/gems/bundler-1.16.1/lib/bundler/vendor/thor/lib/thor.rb:387:in `dispatch'
/home/nathan/.gem/ruby/2.5.0/gems/bundler-1.16.1/lib/bundler/cli.rb:27:in `dispatch'
/home/nathan/.gem/ruby/2.5.0/gems/bundler-1.16.1/lib/bundler/vendor/thor/lib/thor/base.rb:466:in `start'
/home/nathan/.gem/ruby/2.5.0/gems/bundler-1.16.1/lib/bundler/cli.rb:18:in `start'
/home/nathan/.gem/ruby/2.5.0/gems/bundler-1.16.1/exe/bundle:30:in `block in <top (required)>'
/home/nathan/.gem/ruby/2.5.0/gems/bundler-1.16.1/lib/bundler/friendly_errors.rb:122:in `with_friendly_errors'
/home/nathan/.gem/ruby/2.5.0/gems/bundler-1.16.1/exe/bundle:22:in `<top (required)>'
/home/nathan/.gem/ruby/2.5.0/bin/bundle:23:in `load'
/home/nathan/.gem/ruby/2.5.0/bin/bundle:23:in `<main>'

Steps to Reproduce (for bugs)

Minimal demo of behavior here: https://github.com/nwallace/cucumber-index-error-bug
Clone the repo, install ruby 2.5.0 (if necessary), bundle install, cucumber

Your Environment

Version used: 3.1.0
Operating System and version: Arch Linux

The text was updated successfully, but these errors were encountered:

nwallace · 2018-01-30T16:02:04Z

It appears to be caused by the named captures inside the optional group. Without the names, I get a nice error message:

Given /^I am a person( named "(.+) (.+)")?$/ do |first_name, last_name|
  ...
end

$ cucumber
Feature: Demonstrate IndexError bug

  Scenario: It cannot handle this Regexp       # features/index_error.feature:3
    Given I am a person named "Charlotte Rose" # features/step_definitions/error_steps.rb:1
      Single transformer unexpectedly matched 2 values - "Charlotte" and "Rose" (Cucumber::CucumberExpressions::CucumberExpressionError)
      features/index_error.feature:4:in `Given I am a person named "Charlotte Rose"'
    Then my first name is "Charlotte"          # features/step_definitions/error_steps.rb:6
    And my last name is "Rose"                 # features/step_definitions/error_steps.rb:10

Failing Scenarios:
cucumber features/index_error.feature:3 # Scenario: It cannot handle this Regexp

aslakhellesoy · 2018-01-30T16:47:05Z

Hi @nwallace adding support for named capture groups should be easy to do, I'll handle that. When that's fixed, you'll get the same error message as when you use (.*).

Out of curiosity, why did you wrap thefirst_name and last_name capture groups in a surrounding one?

nwallace · 2018-01-30T18:49:08Z

Sometimes I want to specify the person's name and sometimes I don't care what their name is. I was surprised when it worked the way I wanted back on the old version, but it's understandable that that would be hard to parse by cucumber. It's easy enough to just have two separate step definitions 👍

aslakhellesoy · 2018-01-31T00:37:46Z

I've tracked this down to what seems to be a bug in Ruby's RegExp. It turns out a RegExp with a mix of unnamed and named capture groups only exposes access to the named capture groups, and not the unnamed ones.

m = /(a)(?<x>b)/.match('ab')
m.length # => 2
m[0] # => 'ab'
m[1] # => 'b'
m[:x] # => 'b'

There is no way to access the capture group containing the a.

Because of this bug I think our best option is to simply disallow named capture groups in Cucumber.

WDYT?

lock · 2019-01-31T10:55:51Z

This thread has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue for related bugs.

aslakhellesoy added library: cucumber-expressions language: ruby 🐛 bug Defect / Bug labels Jan 30, 2018

aslakhellesoy closed this as completed in 903835f Jan 31, 2018

marcoadkins mentioned this issue Sep 20, 2018

cucumber-expressions: Cucumber treats a (?!text) group as a capturing group; IndexError is then thrown #481

Closed

simondean mentioned this issue Oct 25, 2018

Add step duration to the JSON Formatter cucumber/cucumber-js#125

Closed

lock bot locked as resolved and limited conversation to collaborators Jan 31, 2019

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

cucumber-expressions: index 3 out of matches (IndexError) #329

cucumber-expressions: index 3 out of matches (IndexError) #329

nwallace commented Jan 30, 2018

nwallace commented Jan 30, 2018

aslakhellesoy commented Jan 30, 2018

nwallace commented Jan 30, 2018

aslakhellesoy commented Jan 31, 2018 •

edited

Loading

lock bot commented Jan 31, 2019

cucumber-expressions: index 3 out of matches (IndexError) #329

cucumber-expressions: index 3 out of matches (IndexError) #329

Comments

nwallace commented Jan 30, 2018

Summary

Expected Behavior

Current Behavior

Steps to Reproduce (for bugs)

Your Environment

nwallace commented Jan 30, 2018

aslakhellesoy commented Jan 30, 2018

nwallace commented Jan 30, 2018

aslakhellesoy commented Jan 31, 2018 • edited Loading

lock bot commented Jan 31, 2019

aslakhellesoy commented Jan 31, 2018 •

edited

Loading