tests/cases/compiler/keyofIsLiteralContexualType.ts(5,37): error TS2322: Type 'string' is not assignable to type 'keyof T'.
  Type '"c"' is not assignable to type '"a" | "b"'.
tests/cases/compiler/keyofIsLiteralContexualType.ts(13,11): error TS2339: Property 'b' does not exist on type 'Pick<{ a: number; b: number; c: number; }, "a" | "c">'.


==== tests/cases/compiler/keyofIsLiteralContexualType.ts (2 errors) ====
    // keyof T is a literal contextual type
    
    function foo<T extends { a: string, b: string }>() {
        let a: (keyof T)[] = ["a", "b"];
        let b: (keyof T)[] = ["a", "b", "c"];
                                        ~~~
!!! error TS2322: Type 'string' is not assignable to type 'keyof T'.
!!! error TS2322:   Type '"c"' is not assignable to type '"a" | "b"'.
    }
    
    // Repro from #12455
    
    declare function pick<T, K extends keyof T>(obj: T, propNames: K[]): Pick<T, K>;
    
    let x = pick({ a: 10, b: 20, c: 30 }, ["a", "c"]);
    let b = x.b;  // Error
              ~
!!! error TS2339: Property 'b' does not exist on type 'Pick<{ a: number; b: number; c: number; }, "a" | "c">'.