An error occurred while Style/RedundantFetchBlock cop was inspecting file

[acallaghan]

Hi there,

I've experienced this bug with the Style/RedundantFetchBlock cop today, and it suggested to make a bug report, so here I am.

---

Expected behavior

Rubocop doesn't throw exception

Actual behavior

1 error occurred:
An error occurred while Style/RedundantFetchBlock cop was inspecting -file-
Errors are usually caused by RuboCop bugs.
Please, report your problems to RuboCop's issue tracker.
https://github.com/rubocop-hq/rubocop/issues

Mention the following information in the issue report:
0.86.0 (using Parser 2.7.1.4, rubocop-ast 0.0.3, running on ruby 2.6.4 x86_64-darwin19)
Finished in 1.0352169999969192 seconds

Steps to reproduce the problem

be rubocop -d file

I can't disclose the source file here, but I can try and whittle down a failing case from it if you need it

Backtrace

An error occurred while Style/RedundantFetchBlock cop was inspecting {{file}}
undefined method `basic_literal?' for nil:NilClass
~/.rbenv/versions/2.6.4/lib/ruby/gems/2.6.0/gems/rubocop-0.86.0/lib/rubocop/cop/style/redundant_fetch_block.rb:76:in `basic_literal?'
~/.rbenv/versions/2.6.4/lib/ruby/gems/2.6.0/gems/rubocop-0.86.0/lib/rubocop/cop/style/redundant_fetch_block.rb:52:in `redundant_fetch_block_candidate?'
~/.rbenv/versions/2.6.4/lib/ruby/gems/2.6.0/gems/rubocop-0.86.0/lib/rubocop/cop/style/redundant_fetch_block.rb:48:in `on_block'
~/.rbenv/versions/2.6.4/lib/ruby/gems/2.6.0/gems/rubocop-0.86.0/lib/rubocop/cop/commissioner.rb:56:in `block (2 levels) in trigger_responding_cops'
~/.rbenv/versions/2.6.4/lib/ruby/gems/2.6.0/gems/rubocop-0.86.0/lib/rubocop/cop/commissioner.rb:115:in `with_cop_error_handling'
~/.rbenv/versions/2.6.4/lib/ruby/gems/2.6.0/gems/rubocop-0.86.0/lib/rubocop/cop/commissioner.rb:55:in `block in trigger_responding_cops'
~/.rbenv/versions/2.6.4/lib/ruby/gems/2.6.0/gems/rubocop-0.86.0/lib/rubocop/cop/commissioner.rb:54:in `each'
~/.rbenv/versions/2.6.4/lib/ruby/gems/2.6.0/gems/rubocop-0.86.0/lib/rubocop/cop/commissioner.rb:54:in `trigger_responding_cops'
~/.rbenv/versions/2.6.4/lib/ruby/gems/2.6.0/gems/rubocop-0.86.0/lib/rubocop/cop/commissioner.rb:32:in `block (2 levels) in <class:Commissioner>'
~/.rbenv/versions/2.6.4/lib/ruby/gems/2.6.0/gems/rubocop-ast-0.0.3/lib/rubocop/ast/traversal.rb:114:in `block in on_send'
~/.rbenv/versions/2.6.4/lib/ruby/gems/2.6.0/gems/rubocop-ast-0.0.3/lib/rubocop/ast/traversal.rb:111:in `each'
~/.rbenv/versions/2.6.4/lib/ruby/gems/2.6.0/gems/rubocop-ast-0.0.3/lib/rubocop/ast/traversal.rb:111:in `each_with_index'
~/.rbenv/versions/2.6.4/lib/ruby/gems/2.6.0/gems/rubocop-ast-0.0.3/lib/rubocop/ast/traversal.rb:111:in `on_send'
~/.rbenv/versions/2.6.4/lib/ruby/gems/2.6.0/gems/rubocop-0.86.0/lib/rubocop/cop/commissioner.rb:33:in `block (2 levels) in <class:Commissioner>'
~/.rbenv/versions/2.6.4/lib/ruby/gems/2.6.0/gems/rubocop-ast-0.0.3/lib/rubocop/ast/traversal.rb:57:in `block in on_begin'
~/.rbenv/versions/2.6.4/lib/ruby/gems/2.6.0/gems/rubocop-ast-0.0.3/lib/rubocop/ast/traversal.rb:57:in `each'
~/.rbenv/versions/2.6.4/lib/ruby/gems/2.6.0/gems/rubocop-ast-0.0.3/lib/rubocop/ast/traversal.rb:57:in `on_begin'
~/.rbenv/versions/2.6.4/lib/ruby/gems/2.6.0/gems/rubocop-0.86.0/lib/rubocop/cop/commissioner.rb:33:in `block (2 levels) in <class:Commissioner>'
~/.rbenv/versions/2.6.4/lib/ruby/gems/2.6.0/gems/rubocop-ast-0.0.3/lib/rubocop/ast/traversal.rb:171:in `on_block'
~/.rbenv/versions/2.6.4/lib/ruby/gems/2.6.0/gems/rubocop-0.86.0/lib/rubocop/cop/commissioner.rb:33:in `block (2 levels) in <class:Commissioner>'
~/.rbenv/versions/2.6.4/lib/ruby/gems/2.6.0/gems/rubocop-ast-0.0.3/lib/rubocop/ast/traversal.rb:57:in `block in on_kwbegin'
~/.rbenv/versions/2.6.4/lib/ruby/gems/2.6.0/gems/rubocop-ast-0.0.3/lib/rubocop/ast/traversal.rb:57:in `each'
~/.rbenv/versions/2.6.4/lib/ruby/gems/2.6.0/gems/rubocop-ast-0.0.3/lib/rubocop/ast/traversal.rb:57:in `on_kwbegin'
~/.rbenv/versions/2.6.4/lib/ruby/gems/2.6.0/gems/rubocop-0.86.0/lib/rubocop/cop/commissioner.rb:33:in `block (2 levels) in <class:Commissioner>'
~/.rbenv/versions/2.6.4/lib/ruby/gems/2.6.0/gems/rubocop-ast-0.0.3/lib/rubocop/ast/traversal.rb:57:in `block in on_or_asgn'
~/.rbenv/versions/2.6.4/lib/ruby/gems/2.6.0/gems/rubocop-ast-0.0.3/lib/rubocop/ast/traversal.rb:57:in `each'
~/.rbenv/versions/2.6.4/lib/ruby/gems/2.6.0/gems/rubocop-ast-0.0.3/lib/rubocop/ast/traversal.rb:57:in `on_or_asgn'
~/.rbenv/versions/2.6.4/lib/ruby/gems/2.6.0/gems/rubocop-0.86.0/lib/rubocop/cop/commissioner.rb:33:in `block (2 levels) in <class:Commissioner>'
~/.rbenv/versions/2.6.4/lib/ruby/gems/2.6.0/gems/rubocop-ast-0.0.3/lib/rubocop/ast/traversal.rb:107:in `on_def'
~/.rbenv/versions/2.6.4/lib/ruby/gems/2.6.0/gems/rubocop-0.86.0/lib/rubocop/cop/commissioner.rb:33:in `block (2 levels) in <class:Commissioner>'
~/.rbenv/versions/2.6.4/lib/ruby/gems/2.6.0/gems/rubocop-ast-0.0.3/lib/rubocop/ast/traversal.rb:57:in `block in on_begin'
~/.rbenv/versions/2.6.4/lib/ruby/gems/2.6.0/gems/rubocop-ast-0.0.3/lib/rubocop/ast/traversal.rb:57:in `each'
~/.rbenv/versions/2.6.4/lib/ruby/gems/2.6.0/gems/rubocop-ast-0.0.3/lib/rubocop/ast/traversal.rb:57:in `on_begin'
~/.rbenv/versions/2.6.4/lib/ruby/gems/2.6.0/gems/rubocop-0.86.0/lib/rubocop/cop/commissioner.rb:33:in `block (2 levels) in <class:Commissioner>'
~/.rbenv/versions/2.6.4/lib/ruby/gems/2.6.0/gems/rubocop-ast-0.0.3/lib/rubocop/ast/traversal.rb:99:in `on_class'
~/.rbenv/versions/2.6.4/lib/ruby/gems/2.6.0/gems/rubocop-0.86.0/lib/rubocop/cop/commissioner.rb:33:in `block (2 levels) in <class:Commissioner>'
~/.rbenv/versions/2.6.4/lib/ruby/gems/2.6.0/gems/rubocop-ast-0.0.3/lib/rubocop/ast/traversal.rb:157:in `on_while'
~/.rbenv/versions/2.6.4/lib/ruby/gems/2.6.0/gems/rubocop-0.86.0/lib/rubocop/cop/commissioner.rb:33:in `block (2 levels) in <class:Commissioner>'
~/.rbenv/versions/2.6.4/lib/ruby/gems/2.6.0/gems/rubocop-ast-0.0.3/lib/rubocop/ast/traversal.rb:14:in `walk'
~/.rbenv/versions/2.6.4/lib/ruby/gems/2.6.0/gems/rubocop-0.86.0/lib/rubocop/cop/commissioner.rb:43:in `investigate'
~/.rbenv/versions/2.6.4/lib/ruby/gems/2.6.0/gems/rubocop-0.86.0/lib/rubocop/cop/team.rb:149:in `investigate'
~/.rbenv/versions/2.6.4/lib/ruby/gems/2.6.0/gems/rubocop-0.86.0/lib/rubocop/cop/team.rb:137:in `offenses'
~/.rbenv/versions/2.6.4/lib/ruby/gems/2.6.0/gems/rubocop-0.86.0/lib/rubocop/cop/team.rb:75:in `inspect_file'
~/.rbenv/versions/2.6.4/lib/ruby/gems/2.6.0/gems/rubocop-0.86.0/lib/rubocop/runner.rb:299:in `inspect_file'
~/.rbenv/versions/2.6.4/lib/ruby/gems/2.6.0/gems/rubocop-0.86.0/lib/rubocop/runner.rb:247:in `block in do_inspection_loop'
~/.rbenv/versions/2.6.4/lib/ruby/gems/2.6.0/gems/rubocop-0.86.0/lib/rubocop/runner.rb:279:in `block in iterate_until_no_changes'
~/.rbenv/versions/2.6.4/lib/ruby/gems/2.6.0/gems/rubocop-0.86.0/lib/rubocop/runner.rb:272:in `loop'
~/.rbenv/versions/2.6.4/lib/ruby/gems/2.6.0/gems/rubocop-0.86.0/lib/rubocop/runner.rb:272:in `iterate_until_no_changes'
~/.rbenv/versions/2.6.4/lib/ruby/gems/2.6.0/gems/rubocop-0.86.0/lib/rubocop/runner.rb:243:in `do_inspection_loop'
~/.rbenv/versions/2.6.4/lib/ruby/gems/2.6.0/gems/rubocop-0.86.0/lib/rubocop/runner.rb:122:in `block in file_offenses'
~/.rbenv/versions/2.6.4/lib/ruby/gems/2.6.0/gems/rubocop-0.86.0/lib/rubocop/runner.rb:146:in `file_offense_cache'
~/.rbenv/versions/2.6.4/lib/ruby/gems/2.6.0/gems/rubocop-0.86.0/lib/rubocop/runner.rb:120:in `file_offenses'
~/.rbenv/versions/2.6.4/lib/ruby/gems/2.6.0/gems/rubocop-0.86.0/lib/rubocop/runner.rb:111:in `process_file'
~/.rbenv/versions/2.6.4/lib/ruby/gems/2.6.0/gems/rubocop-0.86.0/lib/rubocop/runner.rb:90:in `block in each_inspected_file'
~/.rbenv/versions/2.6.4/lib/ruby/gems/2.6.0/gems/rubocop-0.86.0/lib/rubocop/runner.rb:89:in `each'
~/.rbenv/versions/2.6.4/lib/ruby/gems/2.6.0/gems/rubocop-0.86.0/lib/rubocop/runner.rb:89:in `reduce'
~/.rbenv/versions/2.6.4/lib/ruby/gems/2.6.0/gems/rubocop-0.86.0/lib/rubocop/runner.rb:89:in `each_inspected_file'
~/.rbenv/versions/2.6.4/lib/ruby/gems/2.6.0/gems/rubocop-0.86.0/lib/rubocop/runner.rb:78:in `inspect_files'
~/.rbenv/versions/2.6.4/lib/ruby/gems/2.6.0/gems/rubocop-0.86.0/lib/rubocop/runner.rb:39:in `run'
~/.rbenv/versions/2.6.4/lib/ruby/gems/2.6.0/gems/rubocop-0.86.0/lib/rubocop/cli/command/execute_runner.rb:21:in `execute_runner'
~/.rbenv/versions/2.6.4/lib/ruby/gems/2.6.0/gems/rubocop-0.86.0/lib/rubocop/cli/command/execute_runner.rb:13:in `run'
~/.rbenv/versions/2.6.4/lib/ruby/gems/2.6.0/gems/rubocop-0.86.0/lib/rubocop/cli/command.rb:10:in `run'
~/.rbenv/versions/2.6.4/lib/ruby/gems/2.6.0/gems/rubocop-0.86.0/lib/rubocop/cli/environment.rb:17:in `run'
~/.rbenv/versions/2.6.4/lib/ruby/gems/2.6.0/gems/rubocop-0.86.0/lib/rubocop/cli.rb:65:in `run_command'
~/.rbenv/versions/2.6.4/lib/ruby/gems/2.6.0/gems/rubocop-0.86.0/lib/rubocop/cli.rb:72:in `execute_runners'
~/.rbenv/versions/2.6.4/lib/ruby/gems/2.6.0/gems/rubocop-0.86.0/lib/rubocop/cli.rb:41:in `run'
~/.rbenv/versions/2.6.4/lib/ruby/gems/2.6.0/gems/rubocop-0.86.0/exe/rubocop:13:in `block in <top (required)>'
~/.rbenv/versions/2.6.4/lib/ruby/gems/2.6.0/gems/rubocop-0.86.0/exe/rubocop:12:in `<top (required)>'
~/.rbenv/versions/2.6.4/bin/rubocop:23:in `load'
~/.rbenv/versions/2.6.4/bin/rubocop:23:in `<top (required)>'

I've redacted parts that weren't relevant

RuboCop version

``
$ bundle exec rubocop -V
0.86.0 (using Parser 2.7.1.4, rubocop-ast 0.0.3, running on ruby 2.6.4 x86_64-darwin19)

[koic]

I can't disclose the source file here, but I can try and whittle down a failing case from it if you need it

Yeah, the minimal reproducible code that happens the error will be a clue to the issue.

[acallaghan]

@koic So i've whittled it down, this generates no rubocop offenses, but triggers the error:

class Master
  def method
    b.fetch(c) {}
  end
end

[koic]

@acallaghan Thanks for showing the reproduction code. I opened PR #8197.