Debug watch throws NoSuchElementException

[asarkar]

Describe the bug

object AtbashCipher:
  private val mapping = ('a' to 'z').toIndexedSeq

  def encode(plain: String): String =
    val cipher = xcode(plain, mapping.size - 1 - _ + 'a')

    cipher.grouped(5).mkString(" ")

  def decode(cipher: String): String =
    xcode(cipher, 'z' - _)

  private def xcode(s: String, f: Char => Int): String =
    val text = for c <- s; x = f(c.toLower); if c.isLetterOrDigit
    yield (if c.isDigit then c else mapping(x))

    text.mkString

When a breakpoint is put on the line yield, and variables c and x added to the watch, the panel throws NoSuchElementException. See screenshot below.

Expected behavior

Watch panel should be able to evaluate expressions.

Operating system

macOS

Editor/Extension

VS Code

Version of Metals

v1.3.5

Extra context or search terms

VSCode version 1.93.0
Scala version 3.4.2
JDK Version 21.0.4

[tgodzik]

This works for me on the newest snapshot of Metals, so this might have actually been already fix. I will try and release a new version of metals soon.

[github-actions]

This issue was closed because no new information was added for the last 30 days. If you have any relevant information, feel free to add it and reopen the issue.

[asarkar]

What more information is required?

[tgodzik]

Ach, I think I forgot to write if you could check the snapshot versions. I was supposed to release a new version, but I keep finding bugs to fix

[asarkar]

Thanks for reopening the ticket. I think I’ll wait for a stable version, no rush. Snapshot might fix this problem but introduce another.

[tgodzik]

Are you able to reproduce it in 1.4.0 Metals version?

[asarkar]

I still am able to reproduce it using 1.4.0 Metals and VSCode 1.95.1

[tgodzik]

Looks like the reason for it is that first stop is not inside the for, but outside of it. @adpi2 any idea is that expected? Might be limitation.

[adpi2]

Looks like the reason for it is that first stop is not inside the for, but outside of it. @adpi2 any idea is that expected? Might be limitation.

Yes the issue is the compiler declares a debug line on the instantiation of the lambda.

In this example:

xs.map { x =>
  x + 1
}

The compiler creates 3 debug lines: one on map, one on x => x + 1 and another one on x + 1. When you stop on x => x + 1, you cannot evaluate x, because it does not exist yet, hence the NoSuchElementException.

[tgodzik]

Looks like this is expected and work as intended. Thanks @adpi2 for adding the additional info.