Autocorrecting Style/LineEndConcatenation changes behaviour

[glowacki-dev]

When using << to append multiple string to array, Style/LineEndConcatenation suggests using \ to join the strings together.

array = []
array << 'Foo' <<
         'Bar' <<
         'Baz'
puts array.join('-')

---

Expected behavior

The way we append strings to array should not be changed. Running corrected code should output Foo-Bar-Baz

Actual behavior

Autocorrect changes the code to use \ instead of << which causes strings to be joined before appending them to the array. Running corrected code outputs FooBarBaz

Steps to reproduce the problem

Autocorrect the code snippet above with rubocop -a

RuboCop version

$ rubocop -V
0.61.1 (using Parser 2.5.3.0, running on ruby 2.5.3 x86_64-linux)

[Drenmi]

Unfortunately we can't know what type a variable dereferences to at runtime using static analysis. What we can do is mark this auto-correction as unsafe in the configuration.

[jaredbeck]

Fixed by #6605