The auxiliary source module did not compile successfully.

Number:rdar://6468393784737 Date Originated:
Status:Open Resolved:
Product:Xcode Product Version:9.4.1(9F2000)
Classification:Serious bug Reproducible:Always
while working on Xcode 9.4.1 (9F2000) playground, i'm constantly seeing an error that says "The auxiliary source module did not compile successfully".

Steps to Reproduce:
create a new file in `Sources` folder and add a generic type (e.g. function, class etc).

Expected Results:
There should not be an error of popped up.

Actual Results:
It pops up with the error as soon as I declare a generic type. 

Xcode 9.4.1(9F2000)


Please note: Reports posted here will not necessarily be seen by Apple. All problems should be submitted at before they are posted here. Please only post information for Radars that you have filed yourself, and please do not include Apple confidential information in your posts. Thank you!