The cop Style/CollectionCompact has unsafe autocorrect which changes calls to Hash#delete_if to Hash#compact.
This is incorrect because Hash#delete_if modifies the object and Hash#compact does not.
The correct replacement would be Hash#compact! (the ! version).

The same applies to Array#delete_if erroneously being converted to Array#compact.
My reproduction below only shows the Hash case. I have not gone looking for other Array / Hash methods that modify the receiver.

Warning: Array#delete_if returns self after modifying the object. Array#compact! sometimes returns nil:
`
$ ri --no-pager Array#compact!
Array#compact!

(from ruby core)

array.compact! -> self or nil

Removes all nil elements from self.

Returns self if any elements removed, otherwise nil.
So maybe it is not as simple as just changingcompacttocompact!` in the replacement.

Expected behavior

I expect a call to Hash#delete_if to be replaced with Hash#compact! (the ! version)

Actual behavior

Hash#delete_if is replaced with Hash#compact (the non ! version)

Steps to reproduce the problem

Example input:

#!/usr/bin/ruby
h = {
  a: "a",
  b: "b",
  c: nil,
}
h.delete_if { |_, v| v.nil? }
pp h

This prints the following:

$ ruby test.rb
{:a=>"a", :b=>"b"}

After letting rubocop correct the source file, the output has changed:

$ rubocop -c /dev/null test.rb  --only Style/CollectionCompact -A
Inspecting 1 file
C

Offenses:

test.rb:8:3: C: [Corrected] Style/CollectionCompact: Use compact instead of delete_if { |_, v| v.nil? }.
h.delete_if { |_, v| v.nil? }
  ^^^^^^^^^^^^^^^^^^^^^^^^^^^

1 file inspected, 1 offense detected, 1 offense corrected

$ ruby test.rb
{:a=>"a", :b=>"b", :c=>nil}

RuboCop version

$ rubocop -V
1.62.1 (using Parser 3.3.0.5, rubocop-ast 1.31.2, running on ruby 3.1.2) +server [x86_64-linux-gnu]