Type errors on computed properties when upgrading to TypeScript 3.7

Which package(s) does this problem pertain to?

• @types/ember__object

Repro steps

The following code reports no typing errors in TypeScript 3.6.3, but gives errors in TypeScript 3.7.2.

declare class MyClass {
  isNew: Ember.ComputedProperty<boolean>
}

function foo(a: MyClass): boolean {
  // TS2322: Type 'ComputedProperty<boolean, boolean>' is not assignable to
  // type 'boolean'.
  return a.isNew
}

function bar(a: MyClass): void {
  // TS2774: This condition will always return true since the function is always
  // defined. Did you mean to call it instead?
  if (a.isNew) {
    // ...
  }
}

The two errors above are likely caused by the same underlying issue. The expected result is no errors upgrading from TS 3.6 to 3.7. This issue was noticed due to new type errors when using the DS.Model.isNew property on instances of Ember Data models.

The workaround appears to be to use get() instead of direct property access.

Thanks.

[chriskrycho]

Hadn’t been any motion, but is likely to be a lot of motion in related spaces starting in about two weeks: we’ve kicked off a “strike team” with the aim of getting official TS support in Ember and things like this will absolutely get addressed as part of that (though the result will be months of effort to get there).

[Alonski]

I am also seeing a similar issue. Here is the code for reference:

const thisIsABool = this.someModel.isNew;
if (thisIsABool) {
  return false;
}