Performance/DeleteSuffix is not safe

[jmkoni]

We had a user of StandardRB open up standardrb/standard#292.

Expected behavior

Currently, if you are using sub to remove a suffix on a Pathname object, it replaces it with delete_suffix, which is not a valid method on a Pathname object. I would expect the following not to change:

path = Pathname.new("path/to/some/ruby/file.rb").sub(/\.rb\z/, "")

This should either not change or the cop should be marked as not safe.

Actual behavior

It changes the above code to:

path = Pathname.new("path/to/some/ruby/file.rb").delete_suffix(".rb")

which results in the following error:

Traceback (most recent call last):
standardrb_bug.rb:3:in `<main>': undefined method `delete_suffix' for #<Pathname:path/to/some/ruby/file.rb> (NoMethodError)

Steps to reproduce the problem

Put the above code in a ruby file, fix the file with Performance/DeleteSuffix enabled. Then try to run the file.

RuboCop version

rubocop 1.14.0
rubocop-performance 1.11.2

[koic]

@jmkoni Thank you for your feedback! JFYI, Performance/DeletePrefix cop has the same false positive.