Style/HashAsLastArrayItem copy with style "no_braces" can result in invalid code

[aried3r]

Expected behavior

Using Style/HashAsLastArrayItem with EnforcedStyle: no_braces should yield valid Ruby code.

I was planning to use braces but wanted to see which parts of our code base might use the no_braces style currently and wanted to see what would change with either of the two styles.

Actual behavior

The cop is not safe and results in invalid Ruby code.

Steps to reproduce the problem

# .rubocop.yml
AllCops:
  NewCops: enable

Style/HashAsLastArrayItem:
  EnforcedStyle: no_braces

# hash_as_last_array_item.rb before
# frozen-string-literal: true

a = [
  {
    foo: :bar
  },
  {
    foo: :baz
  }
]

pp a

$ ruby hash_as_last_array_item.rb
[{:foo=>:bar}, {:foo=>:baz}]

$ rubocop -a hash_as_last_array_item.rb
Inspecting 1 file
E

Offenses:

hash_as_last_array_item.rb:4:3: C: [Corrected] Style/HashAsLastArrayItem: Omit the braces around the hash.
  { ...
  ^
hash_as_last_array_item.rb:6:3: E: Lint/Syntax: unexpected token tCOMMA
(Using Ruby 2.4 parser; configure using TargetRubyVersion parameter, under AllCops)
  ,
  ^
hash_as_last_array_item.rb:7:3: C: [Corrected] Style/HashAsLastArrayItem: Omit the braces around the hash.
  { ...
  ^

1 file inspected, 3 offenses detected, 2 offenses corrected

# hash_as_last_array_item.rb after
# frozen-string-literal: true

a = [
  
    foo: :bar
  ,
  
    foo: :baz
  
]

pp a

$ ruby hash_as_last_array_item.rb
hash_as_last_array_item.rb:6: syntax error, unexpected ',', expecting ']'
hash_as_last_array_item.rb:10: syntax error, unexpected ']', expecting end-of-input

RuboCop version

$ rubocop -V
0.88.0 (using Parser 2.7.1.4, rubocop-ast 0.1.0, running on ruby 2.7.1 x86_64-darwin19)