Only number index type is inferred from `any` computed property key

Bug Report

🔎 Search Terms

• Computed properties
• Indexers
• Index signatures

🕗 Version & Regression Information

• This is the behavior in every version I tried.

⏯ Playground Link

Playground link with relevant code

💻 Code

declare let a: any;

const obj = {
  [a]: "s",
}; // { [x: number]: string }

obj["abc"]; // error

🙁 Actual behavior

A numeric indexer is inferred. String index access marked as invalid.

🙂 Expected behavior

A string indexer is expected. No error for string access.

declare let a: any;

const obj = {
  [a]: "s",
}; // { [x: number]: string }

obj["abc"]; // no error

I created a small PR that addresses the issue as an example but I'm still not sure if the current behavior is intentional or not.

EDIT: I'm still not sure if the inferred indexer should have a String type, perhaps a union of the allowed primitive types fits better, e.g.:

declare let a: any;

const obj = {
  [a]: "s",
}; // { [x: string | number | symbol]: string }

Start with the linked TypeScript Playground reproduction and trace computed-property/indexer inference for an any key. Determine the intended inferred indexer type, then verify the result against the shown string access example and add or update coverage in the relevant type-checking tests.