writeStackTrace now officially has no IO effect anymore for more convenient debugging

lib/system.nim

@@ -3211,9 +3211,10 @@ when not defined(JS): #and not defined(nimscript):
       ## allows you to override the behaviour of your application when CTRL+C
       ## is pressed. Only one such hook is supported.
 
-    proc writeStackTrace*() {.tags: [WriteIOEffect], gcsafe.}
+    proc writeStackTrace*() {.tags: [], gcsafe.}
       ## writes the current stack trace to ``stderr``. This is only works
-      ## for debug builds.
+      ## for debug builds. Since it's usually used for debugging, this
+      ## is proclaimed to have no IO effect!
     when hostOS != "standalone":
       proc getStackTrace*(): string {.gcsafe.}
         ## gets the current stack trace. This only works for debug builds.

lib/system/excpt.nim

@@ -386,9 +386,9 @@ proc writeStackTrace() =
   when hasSomeStackTrace:
     var s = ""
     rawWriteStackTrace(s)
-    showErrorMessage(s)
+    cast[proc (s: string) {.noSideEffect, tags: [], nimcall.}](showErrorMessage)(s)
   else:
-    showErrorMessage("No stack traceback available\n")
+    cast[proc (s: string) {.noSideEffect, tags: [], nimcall.}](showErrorMessage)("No stack traceback available\n")
 
 proc getStackTrace(): string =
   when hasSomeStackTrace: