What is "Ambiguous regexp literal" in rubocop?

Question

The following code

expect(foo).to match /#{MyGem.config.environment_name}/

triggers a rubocop issue

Warning: Ambiguous regexp literal. Parenthesize the method arguments if it's surely a regexp literal, or add a whitespace to the right of the / if it should be a division.

Can someone explain what the issue is and how to resolve it?

Answer 1

Another way to fix this is to simply add parens as rubocop suggests. Change

expect(foo).to match /#{MyGem.config.environment_name}/

to

expect(foo).to match(/#{MyGem.config.environment_name}/)

Answer 2

It is complaining that at this point:

match /#{MyGem.config.environment_name}/

it is unclear whether you're dividing two numbers or passing a RegExp literal to a method call.

In this particulare case, since you're just checking for the presence of a substring within a string, it would be better to use the RSpec #include matcher, like so:

expect(foo).to include MyGem.config.environment_name