Typescript incorrect types

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

• VS Code Version: 1.68.1
• OS Version: Windows_NT x64 10.0.19044

Steps to Reproduce:

1. Open VSCode and create a new text file (Ctrl+N)
2. Set the language to Typescript
3. Paste this code into it:

export interface Foo {
  objs: { id(): string; }[];
}

export class Test {
  private foo: Foo | null = null;

  doSomething(ids: Record<string, boolean>) {
    if (!this.foo) return;
  
    for (let i = 0; i < this.foo.objs.length; i++) {
      const obj = this.foo.objs[i];
      const objId = obj.id();

      if (!ids[objId]) return;
    }
  }
}

1. The type of obj on line 12 is incorrectly identified as any rather than { id(): string; }. This can cause errors in a project with noImplicitAny set to true
2. The Typescript compiler compiles the code without issue, so I believe this is a bug only with the intellisense.

[RyanCavanaugh]

The circularity is this:

• What is the type of obj ? It’s determined by its initializer, what is its type?
• The initializer expression is this.foo.objs[0]. What is its type?
• That depends on whether this.foo is initialized or not. Is it?
• That depends on whether it’s possible to enter this loop body a second time, since the answer to this question controls whether or not the rest of the loop body needs to checked to see if this.foo changes type. Is it possible to enter the loop a second time?
• That depends on ids[objId]. Is this always truthy?
• That depends on whether objId is a statically-knowable index. Is it?
• That depends on its initializer, which is obj.id. What’s the type of that?
• That depends on the type of obj. What is the type of obj? <-- ♻ this is the question being asked

[fatcerberus]

This is just an educated guess, but I’m assuming that obtaining objId from a function short-circuits the check here:

That depends on whether objId is a statically-knowable index. Is it? [No, because it came from a function call.]