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 }

リンクされている TypeScript Playground の再現コードから始め、any キーに対する計算プロパティ／インデクサーの推論を追跡します。意図された推論後のインデクサー型を特定し、その結果を、示されている文字列アクセスの例と照合して検証します。そのうえで、関連する型チェックテストにカバレッジを追加または更新します。