Style/HashConversion: Invalid conversion (undefined method `to_h')

[jdufresne]

Testing using RuboCop commit 2d3e1bc

$ bundle exec rubocop -V
1.9.1 (using Parser 3.0.0.0, rubocop-ast 1.4.1, running on ruby 2.7.2 x86_64-linux)
  - rubocop-performance 1.9.2
  - rubocop-rspec 2.0.1

Input file:

Hash[Integer => BigInteger]

Command

$ bundle exec rubocop -a --only Style/HashConversion ~/test.rb 
Inspecting 1 file
C

Offenses:

/home/jon/test.rb:1:1: C: [Corrected] Style/HashConversion: Prefer ary.to_h to Hash[ary].
Hash[Integer => BigInteger]
^^^^^^^^^^^^^^^^^^^^^^^^^^^

1 file inspected, 1 offense detected, 1 offense corrected

Changed file:

Integer => BigInteger.to_h

Running the code now results in:

NoMethodError (undefined method `to_h' for BigInteger:Class)
Did you mean?  to_s

[RichardsonWTR]

@bbatsov, I've just experienced this same error in Ruby 2.7.1p83.

$ bundle exec rubocop -V
warning: parser/current is loading parser/ruby27, which recognizes
warning: 2.7.2-compliant syntax, but you are running 2.7.1.
warning: please see https://github.com/whitequark/parser#compatibility-with-ruby-mri.
1.10.0 (using Parser 3.0.0.0, rubocop-ast 1.4.1, running on ruby 2.7.1 x86_64-linux)

Input file:

hash1 = { 'some' => 'value', 'another' => 'value'  }
hash2 = { 'some' => 'value'}
hash1_without_hash2 = Hash[hash1.to_a - hash2.to_a]

p hash1_without_hash2

Code result:

$ ruby test.rb 
{"another"=>"value"}

Rubocop execution:

$ bundle exec rubocop test.rb 
warning: parser/current is loading parser/ruby27, which recognizes
warning: 2.7.2-compliant syntax, but you are running 2.7.1.
warning: please see https://github.com/whitequark/parser#compatibility-with-ruby-mri.
Inspecting 1 file
C

Offenses:

test.rb:3:23: C: [Correctable] Style/HashConversion: Prefer ary.to_h to Hash[ary].
hash1_without_hash2 = Hash[hash1.to_a - hash2.to_a]
                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

1 file inspected, 1 offense detected, 1 offense auto-correctable

After the execution of bundle exec rubocop test.rb -a

hash1 = { 'some' => 'value', 'another' => 'value' }
hash2 = { 'some' => 'value' }
hash1_without_hash2 = hash1.to_a - hash2.to_a.to_h

p hash1_without_hash2

Now the script causes an error.

$ ruby test.rb 
Traceback (most recent call last):
        1: from test.rb:3:in `<main>'
test.rb:3:in `-': no implicit conversion of Hash into Array (TypeError)

Can you reopen this issue, or should I open a new issue? By the way, is there a better way to write the above code?

[dvandersluis]

@RichardsonWTR can you make sure you're using the latest version of RuboCop and try again? If the problem persists, create a new ticket please. 🙌

[RichardsonWTR]

Thanks @dvandersluis
No need to open a new ticket.
I've just tested with the 1.12.1 version and Rubocop worked as expected. Pure and simple solution.