How can I get stack trace from exception in Nim?

Question

There's the getStackTrace() function that gets stack trace from the current exception.

But it doesn't work for specific exception, this code won't work error.getStackTrace()

I need it for log function

proc error*(message: string, exception: Exception): void =
    stderr.write_line fmt"      {message}"
    stderr.write_line exception.getStackTrace()

Answer 1

Your sample code does not even compile for me, since getCurrentException returns a reference to an Exception and not a copy of it so there's no way to pass it to error(). Here's a full sample that compiles for me:

proc failHard() =
    doAssert toInt(1.49) == 0

proc error*(message: string, exception: ref Exception) =
    echo message
    echo exception.getStackTrace()

proc main() =
    try: failHard()
    except: error("oops", getCurrentException())

main()

When I compile and run this program I get the following output:

$ ./t
oops
/private/tmp/t/t.nim(12) t
/private/tmp/t/t.nim(9)  main
/private/tmp/t/t.nim(2)  failHard
/Users/gradha/.choosenim/toolchains/nim-1.2.6/lib/system/assertions.nim(29) failedAssertImpl
/Users/gradha/.choosenim/toolchains/nim-1.2.6/lib/system/assertions.nim(22) raiseAssert
/Users/gradha/.choosenim/toolchains/nim-1.2.6/lib/system/fatal.nim(49) sysFatal

Note that getStackTrace() documentation mentions it does not offer much information in non debug builds:

$ nim c -d:release -r t.nim 
Hint: used config file '/Users/gradha/.choosenim/toolchains/nim-1.2.6/config/nim.cfg' [Conf]
Hint: 320 LOC; 0.096 sec; 5.379MiB peakmem; Release build; proj: /private/tmp/t/t.nim; out: /private/tmp/t/t [SuccessX]
Hint: /private/tmp/t/t  [Exec]
oops
fatal.nim(49)            sysFatal