Rubocop crashes on splat operator in case/when block when in auto-correct mode

[rpherbig]

---

Expected behavior

Running rubocop in auto-correct mode should behave the same as normal mode, but also fix as many issues as possible. This is the output in normal mode:

$ rubocop crash.rb
Inspecting 1 file
W

Offenses:

crash.rb:1:11: C: Use %w or %W for an array of words.
results = ['a', 'b']
          ^^^^^^^^^^
crash.rb:2:6: W: Literal 'a' appeared in a condition.
case 'a'
     ^^^
crash.rb:3:1: C: Place when conditions with a splat at the end of the when branches.
when *results, 'c'
^^^^^^^^^^^^^
crash.rb:7:4: C: Final newline missing.
end

Actual behavior

However, rubocop crashes on the same code in auto-correct mode:

$ rubocop --auto-correct crash.rb
Inspecting 1 file


0 files inspected, no offenses detected
undefined method `source_range' for nil:NilClass
c:/Ruby200/lib/ruby/gems/2.0.0/gems/rubocop-0.43.0/lib/rubocop/cop/performance/case_when_splat.rb:126:in `when_branch_range'
c:/Ruby200/lib/ruby/gems/2.0.0/gems/rubocop-0.43.0/lib/rubocop/cop/performance/case_when_splat.rb:110:in `reorder_condition'
c:/Ruby200/lib/ruby/gems/2.0.0/gems/rubocop-0.43.0/lib/rubocop/cop/performance/case_when_splat.rb:86:in `block in autocorrect'
c:/Ruby200/lib/ruby/gems/2.0.0/gems/rubocop-0.43.0/lib/rubocop/cop/corrector.rb:57:in `call'
c:/Ruby200/lib/ruby/gems/2.0.0/gems/rubocop-0.43.0/lib/rubocop/cop/corrector.rb:57:in `block (2 levels) in rewrite'
c:/Ruby200/lib/ruby/gems/2.0.0/gems/parser-2.3.1.4/lib/parser/source/rewriter.rb:194:in `transaction'
c:/Ruby200/lib/ruby/gems/2.0.0/gems/rubocop-0.43.0/lib/rubocop/cop/corrector.rb:56:in `block in rewrite'
c:/Ruby200/lib/ruby/gems/2.0.0/gems/rubocop-0.43.0/lib/rubocop/cop/corrector.rb:54:in `each'
c:/Ruby200/lib/ruby/gems/2.0.0/gems/rubocop-0.43.0/lib/rubocop/cop/corrector.rb:54:in `rewrite'
c:/Ruby200/lib/ruby/gems/2.0.0/gems/rubocop-0.43.0/lib/rubocop/cop/team.rb:145:in `autocorrect_all_cops'
c:/Ruby200/lib/ruby/gems/2.0.0/gems/rubocop-0.43.0/lib/rubocop/cop/team.rb:77:in `autocorrect'
c:/Ruby200/lib/ruby/gems/2.0.0/gems/rubocop-0.43.0/lib/rubocop/cop/team.rb:105:in `block in offenses'
c:/Ruby200/lib/ruby/gems/2.0.0/gems/rubocop-0.43.0/lib/rubocop/cop/team.rb:122:in `investigate'
c:/Ruby200/lib/ruby/gems/2.0.0/gems/rubocop-0.43.0/lib/rubocop/cop/team.rb:101:in `offenses'
c:/Ruby200/lib/ruby/gems/2.0.0/gems/rubocop-0.43.0/lib/rubocop/cop/team.rb:52:in `inspect_file'
c:/Ruby200/lib/ruby/gems/2.0.0/gems/rubocop-0.43.0/lib/rubocop/runner.rb:244:in `inspect_file'
c:/Ruby200/lib/ruby/gems/2.0.0/gems/rubocop-0.43.0/lib/rubocop/runner.rb:191:in `block in do_inspection_loop'
c:/Ruby200/lib/ruby/gems/2.0.0/gems/rubocop-0.43.0/lib/rubocop/runner.rb:223:in `block in iterate_until_no_changes'
c:/Ruby200/lib/ruby/gems/2.0.0/gems/rubocop-0.43.0/lib/rubocop/runner.rb:216:in `loop'
c:/Ruby200/lib/ruby/gems/2.0.0/gems/rubocop-0.43.0/lib/rubocop/runner.rb:216:in `iterate_until_no_changes'
c:/Ruby200/lib/ruby/gems/2.0.0/gems/rubocop-0.43.0/lib/rubocop/runner.rb:187:in `do_inspection_loop'
c:/Ruby200/lib/ruby/gems/2.0.0/gems/rubocop-0.43.0/lib/rubocop/runner.rb:102:in `block in file_offenses'
c:/Ruby200/lib/ruby/gems/2.0.0/gems/rubocop-0.43.0/lib/rubocop/runner.rb:112:in `file_offense_cache'
c:/Ruby200/lib/ruby/gems/2.0.0/gems/rubocop-0.43.0/lib/rubocop/runner.rb:100:in `file_offenses'
c:/Ruby200/lib/ruby/gems/2.0.0/gems/rubocop-0.43.0/lib/rubocop/runner.rb:91:in `process_file'
c:/Ruby200/lib/ruby/gems/2.0.0/gems/rubocop-0.43.0/lib/rubocop/runner.rb:69:in `block in each_inspected_file'
c:/Ruby200/lib/ruby/gems/2.0.0/gems/rubocop-0.43.0/lib/rubocop/runner.rb:66:in `each'
c:/Ruby200/lib/ruby/gems/2.0.0/gems/rubocop-0.43.0/lib/rubocop/runner.rb:66:in `reduce'
c:/Ruby200/lib/ruby/gems/2.0.0/gems/rubocop-0.43.0/lib/rubocop/runner.rb:66:in `each_inspected_file'
c:/Ruby200/lib/ruby/gems/2.0.0/gems/rubocop-0.43.0/lib/rubocop/runner.rb:58:in `inspect_files'
c:/Ruby200/lib/ruby/gems/2.0.0/gems/rubocop-0.43.0/lib/rubocop/runner.rb:37:in `run'
c:/Ruby200/lib/ruby/gems/2.0.0/gems/rubocop-0.43.0/lib/rubocop/cli.rb:72:in `execute_runner'
c:/Ruby200/lib/ruby/gems/2.0.0/gems/rubocop-0.43.0/lib/rubocop/cli.rb:28:in `run'
c:/Ruby200/lib/ruby/gems/2.0.0/gems/rubocop-0.43.0/bin/rubocop:14:in `block in <top (required)>'
c:/Ruby200/lib/ruby/2.0.0/benchmark.rb:296:in `realtime'
c:/Ruby200/lib/ruby/gems/2.0.0/gems/rubocop-0.43.0/bin/rubocop:13:in `<top (required)>'
c:/Ruby200/bin/rubocop:23:in `load'
c:/Ruby200/bin/rubocop:23:in `<main>'

Steps to reproduce the problem

I made a simple ruby file that demonstrates the problem. Run Rubocop on it twice to see the problem (once with auto-correct, once without):

results = ['a', 'b']
case 'a'
when *results, 'c'
  puts 'true'
else
  puts 'false'
end

RuboCop version

$ rubocop -V
0.43.0 (using Parser 2.3.1.4, running on ruby 2.0.0 i386-mingw32)

[rpherbig]

It appears to be CaseWhenSplat which is causing the crash.

[rrosenblum]

@rpherbig, I was not able to reproduce the reported issue with the provided example. I was however able to reproduce the reported issue when there are 2 when branches.

results = ['a', 'b']
case 'a'
when *results, 'c'
  puts 'true'
when results, 'c'
  puts 'true'
else
  puts 'false'
end

I noticed a different issue for the example that you provided. CaseWhenSplat is not auto-correcting the offense that it is registering. I found some examples in the tests for this same scenario. There is a TODO to see if reordering the splat after the other variable will speed up the case statement. I have run a benchmark and determined that it is faster to list all splat expanded variables last.

[8] pry(main)> def splat_first(num)
[8] pry(main)*   case num
[8] pry(main)*   when *FOO, 6, 7, 8  
[8] pry(main)*     true
[8] pry(main)*   else  
[8] pry(main)*     false
[8] pry(main)*   end  
[8] pry(main)* end  
=> :splat_first
[9] pry(main)> def splat_last(num)
[9] pry(main)*   case num
[9] pry(main)*   when 6, 7, 8, *FOO  
[9] pry(main)*     true
[9] pry(main)*   else  
[9] pry(main)*     false
[9] pry(main)*   end  
[9] pry(main)* end  
=> :splat_last

[17] pry(main)> Benchmark.ips do |x|
[17] pry(main)*   x.report('splat first value in splat') { splat_first(3) }
[17] pry(main)*   x.report('splat first value not in splat') { splat_first(7) }
[17] pry(main)*   x.report('splat first no match') { splat_first(0) }
[17] pry(main)*   x.report('splat last value in splat') { splat_last(3) }
[17] pry(main)*   x.report('splat last value not in splat') { splat_last(7) }
[17] pry(main)*   x.report('splat last no match') { splat_last(0) }
[17] pry(main)*   x.compare!
[17] pry(main)* end  
Warming up --------------------------------------
splat first value in splat
                        58.742k i/100ms
splat first value not in splat
                        57.867k i/100ms
splat first no match    53.724k i/100ms
splat last value in splat
                       111.219k i/100ms
splat last value not in splat
                       135.851k i/100ms
 splat last no match   113.707k i/100ms
Calculating -------------------------------------
splat first value in splat
                        708.937k (± 9.9%) i/s -      3.525M in   5.023715s
splat first value not in splat
                        652.417k (± 9.5%) i/s -      3.241M in   5.013931s
splat first no match    631.900k (± 9.0%) i/s -      3.170M in   5.062059s
splat last value in splat
                          1.618M (± 6.4%) i/s -      8.119M in   5.039173s
splat last value not in splat
                          1.907M (± 8.3%) i/s -      9.510M in   5.023153s
 splat last no match      1.483M (± 6.9%) i/s -      7.391M in   5.007247s

Comparison:
splat last value not in splat:    1906993.2 i/s
splat last value in splat:        1618336.7 i/s - 1.18x slower
splat last no match:              1483380.3 i/s - 1.29x slower
splat first value in splat:       708936.7 i/s - 2.69x slower
splat first value not in splat:   652417.0 i/s - 2.92x slower
splat first no match:             631900.4 i/s - 3.02x slower

tldr: There are two things that should be fixed in this cop. The first is the NoMethodError. The second is that we need to auto-correct all splat variables to the end of each when statement.