Exhaustive switch case with returns can mark a finally block as unreachable

🔎 Search Terms

finally switch exhaustive unreachable

🕗 Version & Regression Information

This is the behavior in every version I tried ( doesn't typecheck pre 3.7 ), and I reviewed the FAQ for entries about unreachable code

⏯ Playground Link

https://www.typescriptlang.org/play/?#code/MYewdgzgLgBAhjAvDAFANwFwwIwwD4wBMAlEgHwwDeAUDDFAE4CeVtdMEA7gJZTAAWqNKRrt2wOBACmOLAylQArgzAw0bMROlE5C5avViAvmyMwAZtzBwANjZajx4CCBtSAdDZABzFAHIpAA9eP2JTahNqUEhYACMkISwwRQBbWKkGUkQKR0YHDQ4ePkF0EQK6LRlsXSUVNXKYABMpczhFGyga-XrjUwsrW3tWTWdXDy9fAOCoUPDI6OgYYAT0LFwCEnJh+mZtui5eASEysQrJKq66w1PKnRh5WoMCkzozS2s7fLFuc1RGRSkJxuozcnh8-iCITCvVeEWoUWcsEaK0wMGSaQyWRybDye0KhxKwjxZ201XueiuDWarXanXJjx67BeMDeA0+eJ+fwYAKBI0gYzBk0hM2hTLmQA

💻 Code

const c = (v: 1 | 2) => {
  try {
    switch (v) {
      case 1: return v
      case 2: return v
    }
  } finally {
    if (true) {
      console.log('exit')
    }
  }
}

🙁 Actual behavior

The contents of the finally blocked are marked as unreachable

🙂 Expected behavior

That they are reachable

Additional information about the issue

While the example seems to include some confusing additions the replication apparently requires:

• The cases to be exhaustive
• No default case
• For the switch expression be typed as a literal union of some form
• An if statement to be in the finally block

I assume this is a chaotic mix of unreachable patterns upsetting flow analysis. I've also noticed that it you add an unreachable return statement after the switch then the contents of finally become reachable.