Add explicit conversion Pathname -> String

[radeksimko]

This is related to #8022 and some of our rspec tests (after adding fakefs bootstrap) will fail while calling this code because it relies on automatic conversion from object to String (via to_str).

I first thought I'm gonna send a PR to fakefs to implement the to_str method, but after doing a quick search I rather decided to do explicit conversion here and here's why:
https://www.ruby-forum.com/topic/4405700

I'm actually surprised that the tests are still green on Ruby 2.0.0+.

I was also thinking that we could add it elsewhere where we work with Pathname as String, but this is currently the one place which is heavily covered with tests and which bothers me most + I want to see your feedback on suggested approach first.

Feel free to run the tests with fakefs to see the failures:
https://github.com/radeksimko/homebrew-cask/commit/fe1095b5c81992aaa1e6c39a6afb0931d1191b30

It is only problem when ignoring the shutup helper, so you will need to use the environment variable from here:
#8101

[rolandwalker]

This change does no harm, as it makes explicit what system does implicitly. At some point, before Ruby gets down to invoking execve, everything must become a C array of char.

However, as system always invokes this to_s implicitly, fakefs should be patched as well, if possible. From a quick glance, I wasn't sure whether they intend to cover system at all, or whether they just mock native methods in FileUtils and Pathname.

Fakefs looks like a step in the right direction for us. Our core functionality is changing state on the disk, but we don't always test whether we have changed state on a disk! A relevant recent bug was 2e71e51 – we were really only testing the mocking.

The reason our existing Pathname code works fine (and is conceptually just fine) is the difference between the to_s and to_str methods. We depend on to_s, which is OK because any Pathname (any Object) always has a (perhaps lossy) string representation. We don't depend on to_str, because a Pathname instance doesn't respond to all String methods in a String-like way.

(Though there are plenty of places the distinction is muddied, especially in the test suite. We inherited Pathname#/ from Homebrew, which I find confusing, and would like to remove after #8089).

[rolandwalker]

@radeksimko you were right. We have tons of code that depends on this alias from Homebrew .

This is a case where, because this is the only Ruby project I have worked on, the stuff we implicitly pulled in from Homebrew has warped my understanding of how Ruby actually works. Contrary to what I wrote above, system attempts to_str.

While it's clear which bugs they were addressing with the change to the Pathname class, I'd argue that the behavior of system here is poor. The Pathname arguments are in isolation, there is no other possible interpretation, and paths are something frequently passed to system. So, system ought to invoke to_path.