fixes #5871

lib/system.nim

@@ -442,6 +442,7 @@ type
                                         ## providing an exception message
                                         ## is bad style.
     trace: string
+    up: ref Exception # used for stacking exceptions. Not exported!
 
   SystemError* = object of Exception ## \
     ## Abstract class for exceptions that the runtime system raises.

lib/system/excpt.nim

@@ -73,12 +73,11 @@ proc popSafePoint {.compilerRtl, inl.} =
   excHandler = excHandler.prev
 
 proc pushCurrentException(e: ref Exception) {.compilerRtl, inl.} =
-  #if e.parent.isNil:
+  e.up = currException
-  #  e.parent = currException
   currException = e
 
 proc popCurrentException {.compilerRtl, inl.} =
-  currException = nil # currException.parent
+  currException = currException.up
 
 # some platforms have native support for stack traces:
 const

tests/exception/tfinally3.nim

@@ -1,6 +1,11 @@
 discard """
   file: "tfinally3.nim"
-  output: "false"
+  output: '''false
+Within finally->try
+Traceback (most recent call last)
+tfinally3.nim(24)        tfinally3
+Error: unhandled exception: First [Exception]'''
+  exitCode: 1
 """
 # Test break in try statement:
 
@@ -14,5 +19,11 @@ proc main: bool =
 
 echo main() #OUT false
 
-
+# bug #5871
-
+try:
+  raise newException(Exception, "First")
+finally:
+  try:
+    raise newException(Exception, "Within finally->try")
+  except:
+    echo getCurrentExceptionMsg()