String union types narrowed to falsy should narrow string to ""

Bug Report

🔎 Search Terms

string truthy falsy narrow literal empty

🕗 Version & Regression Information

• This is a crash
• This changed between versions ______ and _______
• This is the behavior in every version I tried, and I reviewed the FAQ for entries about narrowing
• I was unable to test this on prior versions because _______

⏯ Playground Link

Playground link with relevant code

💻 Code

let value = Math.random() > 0.5 && "Some Name";

if (!value) {
  value; // Type: false | string, but should be false | ""
}

🙁 Actual behavior

Inside the narrowed block, value should be false | "", because no other string value is falsy.

🙂 Expected behavior

It's the more general false | string instead.

This was a hard issue to search for; #41503, #33878, and #31156 seemed related but not duplicate to me.

Shoutout to RyanCavanaugh for sending me a code snippet that looked like this -- no good deed goes unpunished in the issue tracker 😄

リンク先の TypeScript Playground で narrowing のケースを再現し、その後、issues #41503、#33878、#31156 の関連する議論を読みます。falsy な文字列のユニオンに対する型チェックの挙動を追跡し、narrowing 後の結果が false と空文字列を区別することを確認します。回帰がカバーされ、報告された型が修正されれば issue は完了です。