NonNullable isn't narrowing down object values' types for optional properties

TypeScript Version: 3.2.0-dev.20181106

Search Terms:
NonNullable object
NonNullable object values

Code

Run the following code via tsc --no-emit --strict test.ts:

interface P {
  color?: 'red' | 'green';
}

type RequiredP = {
  [K in keyof P]: NonNullable<P[K]>;
}

declare const p: RequiredP;
const color: 'red' | 'green' = p.color;

Expected behavior:

The resulting type should not allow undefined for the value at a property color.

Actual behavior:

undefined is still allowed. Using the NonNullable type doesn't seem to have any effect.

Playground Link: Note: you need to enable strictNullChecks manually!
https://www.typescriptlang.org/play/#src=interface%20P%20%7B%0D%0A%20%20color%3F%3A%20'red'%20%7C%20'green'%3B%0D%0A%7D%0D%0A%0D%0Atype%20RequiredP%20%3D%20%7B%0D%0A%20%20%5BK%20in%20keyof%20P%5D%3A%20NonNullable%3CP%5BK%5D%3E%3B%0D%0A%7D%0D%0A%0D%0Adeclare%20const%20p%3A%20RequiredP%3B%0D%0Aconst%20color%3A%20'red'%20%7C%20'green'%20%3D%20p.color%3B%0D%0A

Related Issues:

Reproduisez l’exemple avec TypeScript 3.2.0-dev.20181106 en utilisant tsc --no-emit --strict test.ts, puis comparez-le avec le compilateur actuel et le Playground lié. Examinez la manière dont sont traités les types mappés, les propriétés optionnelles et NonNullable ; le travail est considéré comme terminé lorsque l’affectation déclarée à color rejette undefined tout en conservant le type 'red' | 'green'.