Recursive types highlight error unless narrowed down by using `as` keyword

[khooz]

Does this issue occur when all extensions are disabled?: Yes

• VS Code Version: 1.57.0 (user setup)
• OS Version: Windows_NT x64 10.0.19042
• Commit: b4c1bd0
• Date: 2021-06-09T17:18:42.354Z
• Electron: 12.0.9
• Chrome: 89.0.4389.128
• Node.js: 14.16.0
• V8: 8.9.255.25-electron.0

Steps to Reproduce:

1. Write a recursive interface, eg.

interface SomeType {
   key: string,
   value: string
}

interface RecursiveType {
   [x : string] : RecursiveType | SomeType
}

2. Define a value of the type:

const test : RecursiveType = {
   testKeyOne: {
      nestedOne: {
         key: 'test',
         value: 'test'
      }
   },
   testKeyTwo: {
      nestedOne: {
         nestedTwo: {
            key: 'test',
            value: 'test'
         }
      }
   }
};

3. Use the variable

test.testKeyOne.nestedOne.key;
/* red squiggly line stating:
Property 'nestedOne' does not exist on type 'RecursiveType | SomeType'.
  Property 'nestedOne' does not exist on type 'SomeType'.ts(2339)
*/

(test.testKeyTwo as RecursiveType).nestedOne.nestedTwo.key;
/*
red squiggly line shifts a level deeper stating:
Property 'nestedTwo' does not exist on type 'RecursiveType | SomeType'.
  Property 'nestedTwo' does not exist on type 'SomeType'.ts(2339)
*/

((test.testKeyTwo as RecursiveType).nestedOne as RecuriveType).nestedTwo.key;
/*
red squiggly line goes away and understands that nestedTwo is of type SomeType
*/

I am not sure if this is the limitation of Typescript itself since documentation uses this kind of recursion and the code works without narrowing; but the error highlighting is a nuisance when the code is right. Maybe resolution ordering is the issue at hand, instead of going deep, it should rise up from the deepest possibility.

Screenshot

[IllusionMH]

This is not an issue with editor itself so shouldn't be reported in VS Code repo.

Snd it's also works as expected in TS - your types declared that it's a union and you are trying to access property that may not be available on one of union members. See https://www.typescriptlang.org/docs/handbook/2/everyday-types.html#working-with-union-types

[mjbvz]

Thanks @IllusionMH

Closing this as a question / upstream