Rubocop mistakens plain ruby for rspec DSL

[githubuseracct]

PDK v2.2.0 using rubocop v1.6.1 (pdk enforces the rubocop version, so sorry if this has been fixed already).

Expected behavior

Rubocop would distinguish between plain ruby and rspec DSL.

Actual behavior

Given the line

hosts.each { |_x| install_puppet } unless ENV['BEAKER_provision'] == 'no'

I get

hosts.each { |_x| install_puppet } unless ENV['BEAKER_provision'] == 'no'
^^^^^^^^^^

Steps to reproduce the problem

$ pdk new module whatever --skip-interview
$ cd whatever
$ echo "hosts.each { |_x| install_puppet } unless ENV['BEAKER_provision'] == 'no'" >spec/spec_helper_local.rb
$ pdk bundle exec rubocop --debug spec/spec_helper_local.rb 
pdk (INFO): Using Ruby 2.7.3
pdk (INFO): Using Puppet 7.9.0
warning: parser/current is loading parser/ruby27, which recognizes
warning: 2.7.4-compliant syntax, but you are running 2.7.3.
warning: please see https://github.com/whitequark/parser#compatibility-with-ruby-mri.
For /home/me/whatever: configuration from /home/me/whatever/.rubocop.yml
configuration from /opt/puppetlabs/pdk/share/cache/ruby/2.7.0/gems/rubocop-performance-1.9.1/config/default.yml
configuration from /opt/puppetlabs/pdk/share/cache/ruby/2.7.0/gems/rubocop-performance-1.9.1/config/default.yml
Default configuration from /opt/puppetlabs/pdk/share/cache/ruby/2.7.0/gems/rubocop-1.6.1/config/default.yml
configuration from /opt/puppetlabs/pdk/share/cache/ruby/2.7.0/gems/rubocop-rspec-2.0.1/config/default.yml
configuration from /opt/puppetlabs/pdk/share/cache/ruby/2.7.0/gems/rubocop-rspec-2.0.1/config/default.yml
Inspecting 1 file
Scanning /home/me/whatever/spec/spec_helper_local.rb
C

Offenses:

spec/spec_helper_local.rb:1:1: C: RSpec/IteratedExpectation: Prefer using the all matcher instead of iterating over an array.
hosts.each { |_x| install_puppet } unless ENV['BEAKER_provision'] == 'no'
^^^^^^^^^^

RuboCop version

$ pdk bundle exec rubocop -V
pdk (INFO): Using Ruby 2.7.3
pdk (INFO): Using Puppet 7.9.0
warning: parser/current is loading parser/ruby27, which recognizes
warning: 2.7.4-compliant syntax, but you are running 2.7.3.
warning: please see https://github.com/whitequark/parser#compatibility-with-ruby-mri.
1.6.1 (using Parser 3.0.2.0, rubocop-ast 1.10.0, running on ruby 2.7.3 x86_64-linux)
  - rubocop-performance 1.9.1
  - rubocop-rspec 2.0.1

[pirj]

Tracked it down to .all?:

rubocop-rspec/lib/rubocop/cop/rspec/iterated_expectation.rb:39 RuboCop::Cop::RSpec::IteratedExpectation#on_block:

    36: def on_block(node)
    37:   each?(node) do |arg, body|
    38:     require 'pry'; binding.pry
 => 39:     if single_expectation?(body, arg) || only_expectations?(body, arg)
    40:       add_offense(node.send_node)

here,

only_expectations?(body, arg)
=> true

but

body.child_nodes.count # => 0

only_expectations? is defined as:

          def only_expectations?(body, arg)
            body.each_child_node.all? { |child| expectation?(child, arg) }

which is incorrect for the case when there are no children.
As in:

[].all? { |x| x == 100 } # => true

I'd suggest adding a check:

def only_expectations?(body, arg)
+ body.each_child_node.any? &&
  body.each_child_node.all? { |child| expectation?(child, arg) }
end

Would you like to send a PR, @githubuseracct ?
Your example is quite good to be added as a spec as is.