The changes in src/legacy are not watched

[sulemanof]

Kibana version: master branch

OS version: Windows 10

Browser version: Chrome 74

Original install method (e.g. download page, yum, from source, etc.): yarn start

Describe the bug:
The changes in src/legacy folder are not watched. After a short research, seems the problem appeared after #35406
Not sure about the whole folder, noticed while working in src\legacy\ui\ and src\legacy\core_plugins\metrics folder under Windows 10 OS

Steps to reproduce:

1. Run yarn start
2. Change anything in src/legacy
3. The changes do not cause server restarting

Expected behavior:
The server should be restarted to apply new changes

Screenshots (if relevant):

Errors in browser console (if relevant):

Provide logs and/or server output (if relevant):

Any additional context:

[elasticmachine]

Pinging @elastic/kibana-operations

[peteharverson]

Have also been seeing this exact same sort of issue for the past few days (developing off master) with edits to changes to files inside x-pack/plugins (specifically ml) not triggering optimization. I am developing on Windows 10, but we have also seen the issue on Mac OS). Changes to client side JS files do not seem to be watched at all, and I have had to touch an html file for optimization to run.

I reverted to the commit before #35406 and no longer see the issue - changes to JS files are being watched as expected. It's also worth noting than optimize seems to happen faster before #35406.

[spalger]

Reopening until we resolve the underlying problem.

@sulemanof @peteharverson what editors are you using? We've found some related issues with people using VSCode microsoft/vscode#34634 microsoft/vscode#45295

[mistic]

Yeah I think the problem was not related with the relative cache-loader PR itself. I think the problem is related with the maximum file handles being reached when using vscode as it uses more file handles than the other editors. Are u able to reproduce that problem with vim for example? What is your current max file handle value?

I'm thinking that the problem could be more obvious when used with the relative cache-loader as we change a sourcemaps option to a dynamic thing that could be itself using more file handles make the problem itself more visible.

[sulemanof]

@spalger @mistic
Obviously it's not an editor issue. Tried different: VSCode, JetBrains Webstorm and Vim. Seems that problem was in watching file system in a whole. Changes were not reflected also while operating with git commands (reset, revert and others).

[mistic]

@sulemanof none of us are able to reproduce the problem. As you reported the problem on windows but you also found the problem being happening on Vim for example, are u using an WSL or other bash emulation? If yes, could you please try to reproduce the problem checking out a commit hash before the yesterday revert like for example 0153e59 and then increment your file watchers ? More info could be found here https://webpack.js.org/configuration/watch/#not-enough-watchers

Let me know about the findings please

[mistic]

Problem solved with the revert and another PR without problems were opened #36131