Jest is missing watchman version compatibility checks

[wez]

In facebook/watchman#428 the user rightly reports that the error message is a bit cryptic.

In this case, jest should be using a capability check to gate the use of watch-project.

An example of that can be found in the docs here:

https://facebook.github.io/watchman/docs/nodejs.html#checking-for-watchman-availability

Using literally that check will suffice to catch this specific problem; if the installed watchman server doesn't support relative roots (which is the capability that you need for watch-project to succeed), then the version command will fail with a more descriptive error message, and because you know that it failed during the capability check, you can tailor the jest specific error message to be more directive; just tell the user to upgrade their watchman server.

[thymikee]

This seems like a nice to have, anybody interesting in contributing this check? :)

[Aftabnack]

I call it!

[Aftabnack]

So this is relating to the version of fb-watchman installed?
Upgrading jest will automatically update the version of fb-watchman, is there a scenario when we would have an older version running.

If watchman server is indeed running separately, then I don't remember setting it up for my usage of jest.

How do I recreate this issue? Do I already have watchman installed out of the box on ubuntu? Does jest internally install watchman server when setting it up.

[Aftabnack]

I'm guessing in jest it just falls back to node js file crawler? If watchman is not found?

[thymikee]

Not sure about Ubuntu. Jest doesn't install watchman for you. E.g. on macOS you need brew install watchman. fb-watchman is just a nodejs client: https://github.com/facebook/watchman/tree/master/node

[Aftabnack]

Was just going through the docs. So I cannot test the change.

[Aftabnack]

You can look at PR and the change. If that is enough to close this, go ahead and do so.
Or if you want someone with watchman installed to test this out. Then someone else can take this up.

[Aftabnack]

Someone else can take this up. :)

[DavideDaniel]

after going through various tools including watchman I ended up back here realizing really this is a problem with someone at jest attributing this error in a way that anyone who's not at facebook would be right to be confused - maybe it's just a matter of elaborating the error message

[k-rajat19]

@thymikee how can i test this or reproduce this error. I have installed lower version of fb-watchman but not getting this error and everything works fine.
OS - windows 7 64 bit

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