Conflicting bounds error points to wrong opaque type in the same file

[eejbyfeldt]

Compiler version

Fails on 3.7.3, 3.3.7 and 3.8.0-RC1-bin-20251021-3da7bb1-NIGHTLY

Minimized code

opaque type T >: Int = Int
opaque type O >: Int = Long

Output

[error] ./wrong_alias.scala:1:1
[error] the top-level definitions in package <empty> cannot be instantiated
[error] since it has a member O with possibly conflicting bounds Int | Long <: ... <: Long
[error] opaque type T >: Int = Int
[error] ^
Error compiling project (Scala 3.8.0-RC1-bin-20251021-3da7bb1-NIGHTLY, JVM (21))
Compilation failed

Expectation

The error should be pointing to opaque type O instead.

[hamzaremmal]

Well, it doesn't actually point to the wrong opaque type but rather to a position that was linked to a generated wrapper. We can clearly see that in the the top-level definitions in package <empty> cannot be instantiated.
If we were to wrap the faulty opaque type inside a class, we will get the following error that we can argue is better than what we have:

class Foo:
    opaque type O >: Int = Long

-- Error: test.scala:1:6 -------------------------------------------------------
1 |class Foo:
  |      ^^^
  |class Foo cannot be instantiated since it has a member O with possibly conflicting bounds Long | Int <: ... <: Long
1 error found

Same goes if we change the first statement to anything else but an opaque type.

val x = ???
opaque type O >: Int = Long

-- Error: test.scala:1:0 -------------------------------------------------------
1 |val x = ???
  |^
  |the top-level definitions in package <empty> cannot be instantiated since it has a member O with possibly conflicting bounds Int | Long <: ... <: Long
1 error found

Nevertheless, I agree that this might benefit from a better position (maybe the position of the bad bound) in the error message but looking at the code, this will require some refactoring.