src/a.ts(12,5): error TS2322: Type 'string' is not assignable to type 'number'.
src/b.tsx(3,1): error TS2304: Cannot find name 'foo'.
src/long.ts(7,9): error TS2345: Argument of type '{ a: string; }' is not assignable to parameter of type 'Opts'.
  Property 'b' is missing in type '{ a: string; }' but required in type 'Opts'.