gc:destructors: add first test program

compiler/cgen.nim

@@ -316,7 +316,9 @@ proc resetLoc(p: BProc, loc: var TLoc) =
   let containsGcRef = containsGarbageCollectedRef(loc.t)
   let typ = skipTypes(loc.t, abstractVarRange)
   if isImportedCppType(typ): return
-  if not isComplexValueType(typ):
+  if p.config.selectedGc == gcDestructors and typ.kind in {tyString, tySequence}:
+    linefmt(p, cpsStmts, "$1.len = 0; $1.p = NIM_NIL;$n", rdLoc(loc))
+  elif not isComplexValueType(typ):
     if containsGcRef:
       var nilLoc: TLoc
       initLoc(nilLoc, locTemp, loc.lode, OnStack)

tests/destructor/tgcdestructors.nim

@@ -0,0 +1,17 @@
+discard """
+  cmd: '''nim c --gc:destructors $file'''
+  output: '''1 1'''
+"""
+
+import allocators
+include system / ansi_c
+
+proc main =
+  var s: seq[string] = @[]
+  for i in 0..<80: s.add "foo"
+
+main()
+
+#echo s
+let (a, d) = allocCounters()
+cprintf("%ld %ld\n", a, d)