recoverStackTrace breaks exception message

Consider the following test case:

class ExceptionTest {
    @Test
    fun `should preserve exception message`() {
        Assertions.assertThatThrownBy {
            runBlocking {
                withContext(newFixedThreadPoolContext(10, "my-context")) {
                    throw MyTokenException("42")
                }
            }
        }.isInstanceOf(MyTokenException::class.java).hasMessage("Token 42 is not valid")
    }
}

class MyTokenException(token: String) : RuntimeException("Token $token is not valid")

It is failing on message assertion:

Expecting message to be:
  <"Token 42 is not valid">
but was:
  <"Token Token 42 is not valid is not valid">

It looks like recoverStackTrace / tryCopyException incorrectly recovers the exception. #1040 mentions that similar problem is fixed in 1.2.0, but this test fails on 1.3.2.

[qwwdfsad]

I am not sure we can do better automatically without reflectively hacking Throwable class (that probably will produce a shameful warning on Java 9+), I’ll try to figure it out.

To understand why it happens, I recommend you to get familiar with stacktrace recovery machinery:

The main idea is to reflectively create a copy of the exception, preserving as much information from the original exception as possible. Usually, it is a message and a cause, so we reflectively call a constructor with String parameter and, if possible, with Throwable (or call initCause, whatever) and we cannot potentially know whether this String parameter maps directly to Throwable.message or not.

As a workaround, you can fix this problem by extending CopyableThrowable in your MyTokenException class

[qwwdfsad]

The easiest option is to introspect constructor parameter name using reflection and copy an exception only if the parameter is named “message”. Unfortunately, this functionality is blocked by #1589