Error converting if-then-else-end oneliner

[maagical]

When using the RuboCop linter to autocorrect a one-liner if-then-else-end construct with the --autocorrect option, the resulting code is incorrect. The expected behavior is that the one-liner should be converted to a multi-line construct before the autocorrect is applied, resulting in the correct code.

Expected behavior

When running RuboCop with the --autocorrect option on the one-liner

if matches.size == 1 then matches.first else raise Exception.new :parse_error end

the expected output should be:
with rubocop -A:

raise StandardError, :parse_error unless matches.size == 1
matches.first

or (with only rubocop --autocorrect):

raise Exception, :parse_error unless matches.size == 1
matches.first

Actual behavior

The output generated by RuboCop with the --autocorrect option is incorrect, resulting in the code:

raise Exception.new :parse_error unless matches.size == 1 then matches.first

This code generates a syntax error when run on Rails 7:

./app/models/test.rb:12: syntax error, unexpected `then', expecting `end' or dummy end
...r unless matches.size == 1 then matches.first
... ^~~~

Full Code:

$ rubocop --debug --autocorrect test.rb 
For /var/home/user: Default configuration from /var/home/user/.rvm/gems/ruby-3.2.2/gems/rubocop-1.50.2/config/default.yml
Use parallel by default.
Skipping parallel inspection: only a single file needs inspection
Inspecting 1 file
Scanning /var/home/user/test.rb
Loading cache from /var/home/user/.cache/rubocop_cache/da75a89333f8c1bb0515b8e36c92928c3466edbc/6d7a3b621ca1730e04accd938619e4bdab66cfb1/8eac1b4809748bba093f0ace295341f33f387ef5
F

Offenses:

test.rb:1:1: C: [Corrected] Style/GuardClause: Use a guard clause (raise Exception.new :parse_error unless matches.size == 1) instead of wrapping the code inside a conditional expression.
if matches.size == 1 then matches.first else raise Exception.new :parse_error end 
^^
test.rb:1:1: C: [Corrected] Style/OneLineConditional: Favor the ternary operator (?:) or multi-line constructs over single-line if/then/else/end constructs.
if matches.size == 1 then matches.first else raise Exception.new :parse_error end 
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
test.rb:1:46: C: [Corrected] Style/RaiseArgs: Provide an exception class and message as arguments to raise.
if matches.size == 1 then matches.first else raise Exception.new :parse_error end 
                                             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
test.rb:1:59: F: Lint/Syntax: unexpected token kTHEN
(Using Ruby 2.7 parser; configure using TargetRubyVersion parameter, under AllCops)
raise Exception.new :parse_error unless matches.size == 1 then matches.first   
                                                          ^^^^
test.rb:1:82: C: [Corrected] Layout/TrailingWhitespace: Trailing whitespace detected.
if matches.size == 1 then matches.first else raise Exception.new :parse_error end 
                                                                                 ^

1 file inspected, 5 offenses detected, 4 offenses corrected
Finished in 0.21446587999889744 seconds

Steps to reproduce the problem

Create a file test.rb with the following one-liner:

if matches.size == 1 then matches.first else raise Exception.new :parse_error end

Run the RuboCop linter with the --autocorrect option on the test.rb file:

$ rubocop --autocorrect test.rb

The resulting code generated by RuboCop is:

raise Exception.new :parse_error unless matches.size == 1 then matches.first

RuboCop version

Include the output of rubocop -V or bundle exec rubocop -V if using Bundler.
If you see extension cop versions (e.g. rubocop-performance, rubocop-rspec, and others)
output by rubocop -V, include them as well. Here's an example:

$ rubocop -V
1.50.2 (using Parser 3.2.2.1, rubocop-ast 1.28.1, running on ruby 3.2.2) [x86_64-linux]