`RSpec/LeadingSubject` crashes under TargetRubyVersion: 3.4 with prism

[Drowze]

Steps to reproduce the problem

Given foo_spec.rb:

RSpec.describe "Test" do
  subject { "foo" }
  it
end

Given .rubocop.yml:

AllCops:
  TargetRubyVersion: 3.4
plugins:
  - rubocop-rspec

Running rubocop:

rubocop -d --cache false --only RSpec/LeadingSubject foo_spec.rb

Expected behavior

I expect no unhandled crashes.

Actual behavior

A crash on leading_subject.rb.
(NOTE: the crash does NOT happen if I set ParserEngine to parser_whitequark, so it's likely an issue related to some difference between Parser and Prism)

Some relevant lines of the output:

An error occurred while RSpec/LeadingSubject cop was inspecting /Users/Drowze/workspace/ruby-scripts/rubocop_lsp_bug/foo_spec.rb:2:2.
/Users/Drowze/.local/share/mise/installs/ruby/3.4.7/lib/ruby/gems/3.4.0/gems/rubocop-rspec-3.8.0/lib/rubocop/cop/rspec/leading_subject.rb:67:in 'RuboCop::Cop::RSpec::LeadingSubject#parent': undefined method 'body' for nil (NoMethodError)

          node.each_ancestor(:block).first.body
                                          ^^^^^
        from /Users/Drowze/.local/share/mise/installs/ruby/3.4.7/lib/ruby/gems/3.4.0/gems/rubocop-rspec-3.8.0/lib/rubocop/cop/rspec/leading_subject.rb:59:in 'RuboCop::Cop::RSpec::LeadingSubject#offending_node'
        from /Users/Drowze/.local/share/mise/installs/ruby/3.4.7/lib/ruby/gems/3.4.0/gems/rubocop-rspec-3.8.0/lib/rubocop/cop/rspec/leading_subject.rb:50:in 'RuboCop::Cop::RSpec::LeadingSubject#check_previous_nodes'
        from /Users/Drowze/.local/share/mise/installs/ruby/3.4.7/lib/ruby/gems/3.4.0/gems/rubocop-rspec-3.8.0/lib/rubocop/cop/rspec/leading_subject.rb:44:in 'RuboCop::Cop::RSpec::LeadingSubject#on_block'

Full output (click to expand)

Scanning /Users/Drowze/workspace/ruby-scripts/rubocop_lsp_bug/foo_spec.rb
An error occurred while RSpec/LeadingSubject cop was inspecting /Users/Drowze/workspace/ruby-scripts/rubocop_lsp_bug/foo_spec.rb:2:2.
/Users/Drowze/.local/share/mise/installs/ruby/3.4.7/lib/ruby/gems/3.4.0/gems/rubocop-rspec-3.8.0/lib/rubocop/cop/rspec/leading_subject.rb:67:in 'RuboCop::Cop::RSpec::LeadingSubject#parent': undefined method 'body' for nil (NoMethodError)

          node.each_ancestor(:block).first.body
                                          ^^^^^
        from /Users/Drowze/.local/share/mise/installs/ruby/3.4.7/lib/ruby/gems/3.4.0/gems/rubocop-rspec-3.8.0/lib/rubocop/cop/rspec/leading_subject.rb:59:in 'RuboCop::Cop::RSpec::LeadingSubject#offending_node'
        from /Users/Drowze/.local/share/mise/installs/ruby/3.4.7/lib/ruby/gems/3.4.0/gems/rubocop-rspec-3.8.0/lib/rubocop/cop/rspec/leading_subject.rb:50:in 'RuboCop::Cop::RSpec::LeadingSubject#check_previous_nodes'
        from /Users/Drowze/.local/share/mise/installs/ruby/3.4.7/lib/ruby/gems/3.4.0/gems/rubocop-rspec-3.8.0/lib/rubocop/cop/rspec/leading_subject.rb:44:in 'RuboCop::Cop::RSpec::LeadingSubject#on_block'
        from /Users/Drowze/.local/share/mise/installs/ruby/3.4.7/lib/ruby/gems/3.4.0/gems/rubocop-1.81.7/lib/rubocop/cop/commissioner.rb:107:in 'Kernel#public_send'
        from /Users/Drowze/.local/share/mise/installs/ruby/3.4.7/lib/ruby/gems/3.4.0/gems/rubocop-1.81.7/lib/rubocop/cop/commissioner.rb:107:in 'block (2 levels) in RuboCop::Cop::Commissioner#trigger_responding_cops'
        from /Users/Drowze/.local/share/mise/installs/ruby/3.4.7/lib/ruby/gems/3.4.0/gems/rubocop-1.81.7/lib/rubocop/cop/commissioner.rb:171:in 'RuboCop::Cop::Commissioner#with_cop_error_handling'
        from /Users/Drowze/.local/share/mise/installs/ruby/3.4.7/lib/ruby/gems/3.4.0/gems/rubocop-1.81.7/lib/rubocop/cop/commissioner.rb:106:in 'block in RuboCop::Cop::Commissioner#trigger_responding_cops'
        from /Users/Drowze/.local/share/mise/installs/ruby/3.4.7/lib/ruby/gems/3.4.0/gems/rubocop-1.81.7/lib/rubocop/cop/commissioner.rb:105:in 'Array#each'
        from /Users/Drowze/.local/share/mise/installs/ruby/3.4.7/lib/ruby/gems/3.4.0/gems/rubocop-1.81.7/lib/rubocop/cop/commissioner.rb:105:in 'RuboCop::Cop::Commissioner#trigger_responding_cops'
        from /Users/Drowze/.local/share/mise/installs/ruby/3.4.7/lib/ruby/gems/3.4.0/gems/rubocop-1.81.7/lib/rubocop/cop/commissioner.rb:69:in 'RuboCop::Cop::Commissioner#on_block'
        from /Users/Drowze/.local/share/mise/installs/ruby/3.4.7/lib/ruby/gems/3.4.0/gems/rubocop-ast-1.48.0/lib/rubocop/ast/traversal.rb:147:in 'block in RuboCop::AST::Traversal#on_dstr'
        from /Users/Drowze/.local/share/mise/installs/ruby/3.4.7/lib/ruby/gems/3.4.0/gems/rubocop-ast-1.48.0/lib/rubocop/ast/traversal.rb:147:in 'Array#each'
        from /Users/Drowze/.local/share/mise/installs/ruby/3.4.7/lib/ruby/gems/3.4.0/gems/rubocop-ast-1.48.0/lib/rubocop/ast/traversal.rb:147:in 'RuboCop::AST::Traversal#on_dstr'
        from /Users/Drowze/.local/share/mise/installs/ruby/3.4.7/lib/ruby/gems/3.4.0/gems/rubocop-1.81.7/lib/rubocop/cop/commissioner.rb:71:in 'RuboCop::Cop::Commissioner#on_begin'
        from /Users/Drowze/.local/share/mise/installs/ruby/3.4.7/lib/ruby/gems/3.4.0/gems/rubocop-ast-1.48.0/lib/rubocop/ast/traversal.rb:169:in 'RuboCop::AST::Traversal#on_itblock'
        from /Users/Drowze/.local/share/mise/installs/ruby/3.4.7/lib/ruby/gems/3.4.0/gems/rubocop-1.81.7/lib/rubocop/cop/commissioner.rb:71:in 'RuboCop::Cop::Commissioner#on_itblock'
        from /Users/Drowze/.local/share/mise/installs/ruby/3.4.7/lib/ruby/gems/3.4.0/gems/rubocop-ast-1.48.0/lib/rubocop/ast/traversal.rb:20:in 'RuboCop::AST::Traversal#walk'
        from /Users/Drowze/.local/share/mise/installs/ruby/3.4.7/lib/ruby/gems/3.4.0/gems/rubocop-1.81.7/lib/rubocop/cop/commissioner.rb:87:in 'RuboCop::Cop::Commissioner#investigate'
        from /Users/Drowze/.local/share/mise/installs/ruby/3.4.7/lib/ruby/gems/3.4.0/gems/rubocop-1.81.7/lib/rubocop/cop/team.rb:174:in 'RuboCop::Cop::Team#investigate_partial'
        from /Users/Drowze/.local/share/mise/installs/ruby/3.4.7/lib/ruby/gems/3.4.0/gems/rubocop-1.81.7/lib/rubocop/cop/team.rb:108:in 'RuboCop::Cop::Team#investigate'
        from /Users/Drowze/.local/share/mise/installs/ruby/3.4.7/lib/ruby/gems/3.4.0/gems/rubocop-1.81.7/lib/rubocop/runner.rb:350:in 'block in RuboCop::Runner#inspect_file'
        from /Users/Drowze/.local/share/mise/installs/ruby/3.4.7/lib/ruby/gems/3.4.0/gems/rubocop-1.81.7/lib/rubocop/runner.rb:349:in 'Array#each'
        from /Users/Drowze/.local/share/mise/installs/ruby/3.4.7/lib/ruby/gems/3.4.0/gems/rubocop-1.81.7/lib/rubocop/runner.rb:349:in 'Enumerable#flat_map'
        from /Users/Drowze/.local/share/mise/installs/ruby/3.4.7/lib/ruby/gems/3.4.0/gems/rubocop-1.81.7/lib/rubocop/runner.rb:349:in 'RuboCop::Runner#inspect_file'
        from /Users/Drowze/.local/share/mise/installs/ruby/3.4.7/lib/ruby/gems/3.4.0/gems/rubocop-1.81.7/lib/rubocop/runner.rb:291:in 'block in RuboCop::Runner#do_inspection_loop'
        from /Users/Drowze/.local/share/mise/installs/ruby/3.4.7/lib/ruby/gems/3.4.0/gems/rubocop-1.81.7/lib/rubocop/runner.rb:326:in 'block in RuboCop::Runner#iterate_until_no_changes'
        from <internal:kernel>:168:in 'Kernel#loop'
        from /Users/Drowze/.local/share/mise/installs/ruby/3.4.7/lib/ruby/gems/3.4.0/gems/rubocop-1.81.7/lib/rubocop/runner.rb:319:in 'RuboCop::Runner#iterate_until_no_changes'
        from /Users/Drowze/.local/share/mise/installs/ruby/3.4.7/lib/ruby/gems/3.4.0/gems/rubocop-1.81.7/lib/rubocop/runner.rb:287:in 'RuboCop::Runner#do_inspection_loop'
        from /Users/Drowze/.local/share/mise/installs/ruby/3.4.7/lib/ruby/gems/3.4.0/gems/rubocop-1.81.7/lib/rubocop/runner.rb:167:in 'block in RuboCop::Runner#file_offenses'
        from /Users/Drowze/.local/share/mise/installs/ruby/3.4.7/lib/ruby/gems/3.4.0/gems/rubocop-1.81.7/lib/rubocop/runner.rb:192:in 'RuboCop::Runner#file_offense_cache'
        from /Users/Drowze/.local/share/mise/installs/ruby/3.4.7/lib/ruby/gems/3.4.0/gems/rubocop-1.81.7/lib/rubocop/runner.rb:166:in 'RuboCop::Runner#file_offenses'
        from /Users/Drowze/.local/share/mise/installs/ruby/3.4.7/lib/ruby/gems/3.4.0/gems/rubocop-1.81.7/lib/rubocop/runner.rb:154:in 'RuboCop::Runner#process_file'
        from /Users/Drowze/.local/share/mise/installs/ruby/3.4.7/lib/ruby/gems/3.4.0/gems/rubocop-1.81.7/lib/rubocop/runner.rb:135:in 'block in RuboCop::Runner#each_inspected_file'
        from /Users/Drowze/.local/share/mise/installs/ruby/3.4.7/lib/ruby/gems/3.4.0/gems/rubocop-1.81.7/lib/rubocop/runner.rb:134:in 'Array#each'
        from /Users/Drowze/.local/share/mise/installs/ruby/3.4.7/lib/ruby/gems/3.4.0/gems/rubocop-1.81.7/lib/rubocop/runner.rb:134:in 'Enumerable#reduce'
        from /Users/Drowze/.local/share/mise/installs/ruby/3.4.7/lib/ruby/gems/3.4.0/gems/rubocop-1.81.7/lib/rubocop/runner.rb:134:in 'RuboCop::Runner#each_inspected_file'
        from /Users/Drowze/.local/share/mise/installs/ruby/3.4.7/lib/ruby/gems/3.4.0/gems/rubocop-1.81.7/lib/rubocop/runner.rb:120:in 'RuboCop::Runner#inspect_files'
        from /Users/Drowze/.local/share/mise/installs/ruby/3.4.7/lib/ruby/gems/3.4.0/gems/rubocop-1.81.7/lib/rubocop/runner.rb:73:in 'RuboCop::Runner#run'
        from /Users/Drowze/.local/share/mise/installs/ruby/3.4.7/lib/ruby/gems/3.4.0/gems/rubocop-1.81.7/lib/rubocop/cli/command/execute_runner.rb:26:in 'block in RuboCop::CLI::Command::ExecuteRunner#execute_runner'
        from /Users/Drowze/.local/share/mise/installs/ruby/3.4.7/lib/ruby/gems/3.4.0/gems/rubocop-1.81.7/lib/rubocop/cli/command/execute_runner.rb:52:in 'RuboCop::CLI::Command::ExecuteRunner#with_redirect'
        from /Users/Drowze/.local/share/mise/installs/ruby/3.4.7/lib/ruby/gems/3.4.0/gems/rubocop-1.81.7/lib/rubocop/cli/command/execute_runner.rb:25:in 'RuboCop::CLI::Command::ExecuteRunner#execute_runner'
        from /Users/Drowze/.local/share/mise/installs/ruby/3.4.7/lib/ruby/gems/3.4.0/gems/rubocop-1.81.7/lib/rubocop/cli/command/execute_runner.rb:17:in 'RuboCop::CLI::Command::ExecuteRunner#run'
        from /Users/Drowze/.local/share/mise/installs/ruby/3.4.7/lib/ruby/gems/3.4.0/gems/rubocop-1.81.7/lib/rubocop/cli/command.rb:11:in 'RuboCop::CLI::Command.run'
        from /Users/Drowze/.local/share/mise/installs/ruby/3.4.7/lib/ruby/gems/3.4.0/gems/rubocop-1.81.7/lib/rubocop/cli/environment.rb:18:in 'RuboCop::CLI::Environment#run'
        from /Users/Drowze/.local/share/mise/installs/ruby/3.4.7/lib/ruby/gems/3.4.0/gems/rubocop-1.81.7/lib/rubocop/cli.rb:128:in 'RuboCop::CLI#run_command'
        from /Users/Drowze/.local/share/mise/installs/ruby/3.4.7/lib/ruby/gems/3.4.0/gems/rubocop-1.81.7/lib/rubocop/cli.rb:135:in 'RuboCop::CLI#execute_runners'
        from /Users/Drowze/.local/share/mise/installs/ruby/3.4.7/lib/ruby/gems/3.4.0/gems/rubocop-1.81.7/lib/rubocop/cli.rb:54:in 'block in RuboCop::CLI#run'
        from /Users/Drowze/.local/share/mise/installs/ruby/3.4.7/lib/ruby/gems/3.4.0/gems/rubocop-1.81.7/lib/rubocop/cli.rb:87:in 'RuboCop::CLI#profile_if_needed'
        from /Users/Drowze/.local/share/mise/installs/ruby/3.4.7/lib/ruby/gems/3.4.0/gems/rubocop-1.81.7/lib/rubocop/cli.rb:45:in 'RuboCop::CLI#run'
        from /Users/Drowze/.local/share/mise/installs/ruby/3.4.7/lib/ruby/gems/3.4.0/gems/rubocop-1.81.7/exe/rubocop:15:in '<top (required)>'
        from /Users/Drowze/.local/share/mise/installs/ruby/3.4.7/bin/rubocop:25:in 'Kernel#load'
        from /Users/Drowze/.local/share/mise/installs/ruby/3.4.7/bin/rubocop:25:in '<main>'
.

1 file inspected, no offenses detected

1 error occurred:
An error occurred while RSpec/LeadingSubject cop was inspecting /Users/Drowze/workspace/ruby-scripts/rubocop_lsp_bug/foo_spec.rb:2:2.
configuration from /Users/Drowze/workspace/ruby-scripts/rubocop_lsp_bug/.rubocop.yml
Errors are usually caused by RuboCop bugs.
Please, update to the latest RuboCop version if not already in use, and report a bug if the issue still occurs on this version.
https://github.com/rubocop/rubocop/issues

Mention the following information in the issue report:
1.81.7 (using Parser 3.3.10.0, rubocop-ast 1.48.0, analyzing as Ruby 2.7, running on ruby 3.4.7) [arm64-darwin24]
Finished in 0.11606499998015352 seconds

RuboCop RSpec version

$ rubocop -V
1.81.7 (using Parser 3.3.10.0, Prism 1.6.0, rubocop-ast 1.48.0, analyzing as Ruby 3.4, running on ruby 3.4.7) [arm64-darwin24]
  - rubocop-rspec 3.8.0

[Drowze]

I suppose this is discrepancy in prism vs parser due to ruby 3.4 "it" default block parameter.

Using prism's binary utility to confirm the difference:

prism parser -e 'RSpec.describe "Test" do
  it
end'

Output:

Parser:
s(:block,
  s(:send,
    s(:const, nil, :RSpec), :describe,
    s(:str, "Test")),
  s(:args),
  s(:send, nil, :it))

Prism:
s(:itblock,
  s(:send,
    s(:const, nil, :RSpec), :describe,
    s(:str, "Test")), :it,
  s(:lvar, :it))

Note that prism treats it as a variable (s(:lvar, :it)), while parser treats as a method call (s(:send, nil, :it)).
Another relevant, simpler example:

$ prism parser -e 'foo { it }'

Parser:
s(:block,
  s(:send, nil, :foo),
  s(:args),
  s(:send, nil, :it))

Prism:
s(:itblock,
  s(:send, nil, :foo), :it,
  s(:lvar, :it))

Pull request that added itblock support to prism: ruby/prism#3481