Does rootDir need to be required in tsconfig?

[billyzkid]

Not all typescript projects need a rootDir configured for building the project. Can we eliminate this extra requirement for copying?

[bencergazda]

It would be great! Do you think we can use TS API to find out the rootDir?

[jrencz]

Also: if rootDirs is used instead of rootDir it fails.
(Since this issue exists I'm attaching this finding here instead of creating a separate issue)