Thanks!

Could you tell me some more about how this problem presented please? I haven't noticed a related issue being raised and so I'd like to understand the context for this.

As stated in #736, I got the following error when I turned on experimentalWatchApi:

Module build failed: RangeError: The normalization form should be one of NFC, NFD, NFKC, NFKD.
    at String.normalize (<anonymous>)
    at Object.directoryExists (d:\git\project\node_modules\ts-loader\dist\servicesHost.js:112:68)
    at Object.compilerHost.directoryExists (d:\git\project\node_modules\typescript\lib\typescript.js:77404:121)
    at d:\git\project\node_modules\typescript\lib\typescript.js:23409:22
    at Object.forEachAncestorDirectory (d:\git\project\node_modules\typescript\lib\typescript.js:11141:26)
    at getDefaultTypeRoots (d:\git\project\node_modules\typescript\lib\typescript.js:23407:12)
    at getEffectiveTypeRoots (d:\git\project\node_modules\typescript\lib\typescript.js:23393:20)
    at resolveTypeReferenceDirective (d:\git\project\node_modules\typescript\lib\typescript.js:23425:25)
    at resolveNamesWithLocalCache (d:\git\project\node_modules\typescript\lib\typescript.js:76752:38)
    at Object.resolveTypeReferenceDirectives (d:\git\project\node_modules\typescript\lib\typescript.js:76804:20)

Our project previously used the happyPack mode, so we don't have any previous history to go by. But the offending change, 388f2a6 8 days ago, has only been included in the 4.0.0 release from 5 days ago so far.

Yup - totally my bad. Me and my refactoring 😄

Thanks for the fix; I'll merge and release this as 4.0.1. Hopefully sometime this weekend. Thanks again for pitching in!

Released - thanks for your help!

No problem. I tried playing around with a fixed version locally today when I had time, but ran into hangs during webpack that I couldn't reproduce in a minimal repo (with experimentalWatchApi, to be clear). Are there any diagnostics I could leverage in any future investigation?

You could try using the trace functionality (set traceResolution: true in your tsconfig.json) which might help. Otherwise the easiest thing to do is hack console logs into it whilst you're investigating.

Basic, but it suffices!