100% CPU when installing node_modules while a file is open #30208

TypeScript Version: typescript@3.4.0-dev.20190302

Search Terms: tsserver cpu ember reload

Steps to reproduce

This is super-verbose; the relevant steps are bold and should be easy to reproduce

• Tested in MacOS
• Clone https://github.com/phil294/tsserver_lag_demo2. (It includes just a few dependencies with which the issue can be reproduced)
• Open it up in vscode
• Open process explorer so you can see the CPU usage of tsserver
• Do not open main.js (if you already have, close the tab & reload)
• Run rm -rf node_modules && yarn
• Wait for it to finish
• Open main.js
• tsserver cpu goes up to 50% for ~1 second. This is how it should be
• Keep main.js open
• Run rm -rf node_modules && yarn
• Wait for it to finish

Expected behavior:

tsserver should not go mad

Actual behavior:

tsserver cpu goes up to 100% and stays like this for a long time. It varies, but I've had both 30 seconds and 15 minutes. It renders the entire intellisense and go-to mechanics useless. Reinstalling node_modules is one of the most common things to do in a JS/TS project. This bug makes developing Ember.js applications with vscode & typescript intellisense support effectively impossible. For example, in our team, we all had to go back to Sublime Text because of this. The CPU usage is probably related to some dependency in package.json, but I have not been able to narrow it down. Either way, it is a Typescript bug.

Related Issues:
There are multiple tsserver CPU related issues. This one was the most similar but is missing details and is also closed, so probably not related.