tsconfig.json extends impossible to cancel / override previous settings

[pocesar]

TypeScript Version: 2.1.1 / nightly (2.2.0-dev.201xxxxx)

Code

// tsconfig.json
{
   "compilerOptions": {
     "outFile": "dist/app.js"
   }
}
// extends.json
{
   "extends": "./tsconfig.json",
   "compilerOptions": {
       "outFile": null,
       "outDir": "mapped"
   }
}

Expected behavior:

Be able to "cancel" previous outFile setting by setting the "outFile" to null in the extended version

Actual behavior:

error TS5024: Compiler option 'outFile' requires a value of type string.

if outFile is set to "", it tries to write to . giving a ESDIR error in Node

[pocesar]

ok, it seems that it needs to be the otherway around, the base minimum in a base.json and then "extends": "base.json" inside tsconfig.json and vendor.json with only the settings not defined in base.json

[mhegazy]

We have a few reports for this already in #16838 and #17357, we should fix this.