missing getter is undetected TS error, runtime error

[bunnybones1]

TypeScript Version: 3.8.3

Search Terms:
missing getter setter

Code

class A {
  label:string = 'test'
}

class B {
  private _a:A
  set a(val:A) { this._a = val }
  constructor() { this._a = new A() }
}
const b = new B()
b.a.label = 'hello' //b.a will always be undefined due to missing getter, but still somehow gets b.a's type from the setter, and will cause no TS errors

Expected behavior:

Error: no 'a' property on class 'B'

OR

Error: class 'B' is missing a getter for property 'a'

(P.S. maybe b.a should not resolve to type 'A' just because that is the setter type)

Actual behavior:

Compiles fine. Variable has value undefined at runtime.

Playground Link:
Playground Link

Related Issues:
#30852

[arilotter]

+1 A getter without a setter is well-defined in TS (readonly) but a setter without a getter should either use some writeonly modifier ( #21759 ) or fail to compile entirely, since TS's type system won't complain and you'll get runtime errors.

[bunnybones1]

Hey @RyanCavanaugh
I'm aware of #30852 but it's closed and unresolved, so I wasn't sure how to proceed.

[typescript-bot]

This issue has been marked as a 'Duplicate' and has seen no recent activity. It has been automatically closed for house-keeping purposes.