fixes #8847

lib/system.nim

@@ -3972,7 +3972,7 @@ proc addQuoted*[T](s: var string, x: T) =
   ##   tmp.add(", ")
   ##   tmp.addQuoted('c')
   ##   assert(tmp == """1, "string", 'c'""")
-  when T is string:
+  when T is string or T is cstring:
     s.add("\"")
     for c in x:
       # Only ASCII chars are escaped to avoid butchering

tests/system/tostring.nim

@@ -106,4 +106,12 @@ var nilstring: string
 bar(nilstring)
 
 static:
-  stringCompare()
+  stringCompare()
+
+# bug 8847
+var a2: cstring = "fo\"o2"
+
+block:
+  var s: string
+  s.addQuoted a2
+  doAssert s == "\"fo\\\"o2\""