Do no watch parent directory of dirs

[y-yagi]

EventedFileUpdateChecker will search the parent directory if the specified directory does not exist.

Since test/mailers/previews is included in the watch target by default, if there is no test directory (e.g. using rspec), the Rails root directory will be included in the watch target.

$ rails new app
$ cd app
$ ./bin/rails r "p Rails.application.reloaders.last.send(:directories_to_watch).include?(Rails.root)"
false
$ rm -rf test
$ ./bin/rails r "p Rails.application.reloaders.last.send(:directories_to_watch).include?(Rails.root)"
true

This causes node_modules to be included in watch target. Adding parent directories to watch target may include unexpected directories. I think it should be avoided.

Related to #32700.

[matthewd]

I think we'd need the EventedFileUpdateChecker to poll for the existence of any paths it's omitting here: the reason it currently watches the parents [and ultimately, the root] is that someone could create that directory, and then put a file in it, and if we don't notice.. that's bad.

[y-yagi]

I have some doubt whether the case that the directory will be added later is actually there, but indeed I think that the point is right. Thanks.

However, I want to prevent node_modules from being watched.
For example, in the case of Guard, this problem can be avoided by explicitly specifying the directory to be watched, but in the current EventedFileUpdateChecker this can not be done.
https://github.com/guard/listen/wiki/Duplicate-directory-errors#case-of-a-guardfile

Therefore,

• Add config to specify directory to ignore
• Ignore node_modules directory by default in EventedFileUpdateChecker(It seems that listen have the plan. Ignore node_modules directory by default  guard/listen#338)

I'd like to do one of the fixes, what do you think?

[rafaelfranca]

Let's go with Add config to specify directory to ignore and have node_modules there by default.

[matthewd]

Sorry, to be clear, I wasn't claiming the current behaviour is necessary -- I was suggesting a third option:

• Use events to watch the directories that exist, and use polling to check that any initially-absent ones haven't appeared.

[dhh]

Whatever we go with, it would be great to have something at least temporary on rails/master. I can't record the video for Action Mailbox while this issue is there present 😄. (Well, at least not using rails/master).

[y-yagi]

@matthewd Does "polling" mean listen's polling adapter, right?

In my understanding, since the polling adapter cannot be specified for directories that do not exist, I think that it is necessary to watch the parent directory (probably the root of the Rails application).
In that case, all of the files of node_modules are subject to polling, and the load does not matter?

[matthewd]

@y-yagi I was thinking something along these lines: https://gist.github.com/matthewd/820e2100f45aa1011746ebec025a3acc

(Totally untested, just a sketch.)

[y-yagi]

@matthewd Thanks for clearing. I updated the PR with that approach.

[matthewd]

Awesome, thanks! ❤️

Do you think it's worth adding a test that we don't watch a node_modules-like sibling of a missing directory? Or maybe that's too specific to the old behaviour. 🤔

[matthewd]

I sneaky-edited which gist my comment was pointing to... just after posting I realised this needs to re-check the conditional inside the lock: Process.pid can't have changed, but @pid might've been fixed by another thread that did the following while we were waiting for the mutex.

[y-yagi]

Do you think it's worth adding a test that we don't watch a node_modules-like sibling of a missing directory?

Thank you for pointing out. I think that test should be. I updated.