Fix #12676 (#13634)

lib/system/nimscript.nim

@@ -26,13 +26,10 @@ template builtin = discard
 # We know the effects better than the compiler:
 {.push hint[XDeclaredButNotUsed]: off.}
 
-proc listDirs*(dir: string): seq[string] =
-  ## Lists all the subdirectories (non-recursively) in the directory `dir`.
-  builtin
-proc listFiles*(dir: string): seq[string] =
-  ## Lists all the files (non-recursively) in the directory `dir`.
-  builtin
-
+proc listDirsImpl(dir: string): seq[string] {.
+  tags: [ReadIOEffect], raises: [OSError].} = builtin
+proc listFilesImpl(dir: string): seq[string] {.
+  tags: [ReadIOEffect], raises: [OSError].} = builtin
 proc removeDir(dir: string) {.
   tags: [ReadIOEffect, WriteIOEffect], raises: [OSError].} = builtin
 proc removeFile(dir: string) {.
@@ -47,6 +44,7 @@ proc copyDir(src, dest: string) {.
   tags: [ReadIOEffect, WriteIOEffect], raises: [OSError].} = builtin
 proc createDir(dir: string) {.tags: [WriteIOEffect], raises: [OSError].} =
   builtin
+
 proc getError: string = builtin
 proc setCurrentDir(dir: string) = builtin
 proc getCurrentDir*(): string =
@@ -196,6 +194,16 @@ template log(msg: string, body: untyped) =
   if mode != ScriptMode.WhatIf:
     body
 
+proc listDirs*(dir: string): seq[string] =
+  ## Lists all the subdirectories (non-recursively) in the directory `dir`.
+  result = listDirsImpl(dir)
+  checkOsError()
+
+proc listFiles*(dir: string): seq[string] =
+  ## Lists all the files (non-recursively) in the directory `dir`.
+  result = listFilesImpl(dir)
+  checkOsError()
+
 proc rmDir*(dir: string) {.raises: [OSError].} =
   ## Removes the directory `dir`.
   log "rmDir: " & dir: