fixes nim-lang#22680 Nim zero clear an object inherits C++ imported c…

…lass when a proc return it

compiler/cgen.nim

@@ -498,10 +498,17 @@ proc resetLoc(p: BProc, loc: var TLoc) =
     else:
       # array passed as argument decayed into pointer, bug #7332
       # so we use getTypeDesc here rather than rdLoc(loc)
-      if not isOrHasImportedCppType(typ): #bug 22679
+      let tyDesc = getTypeDesc(p.module, loc.t, descKindFromSymKind mapTypeChooser(loc))
+      if isOrHasImportedCppType(typ): 
+        if lfIndirect in loc.flags: 
+          #C++ cant be just zeroed. We need to call the ctors
+          var tmp = getTemp(p, loc.t)
+          linefmt(p, cpsStmts,"#nimCopyMem((void*)$1, (NIM_CONST void*)$2, sizeof($3));$n",
+                  [addrLoc(p.config, loc), addrLoc(p.config, tmp), tyDesc])
+      else:
         linefmt(p, cpsStmts, "#nimZeroMem((void*)$1, sizeof($2));$n",
-                [addrLoc(p.config, loc),
-                getTypeDesc(p.module, loc.t, descKindFromSymKind mapTypeChooser(loc))])
+                [addrLoc(p.config, loc), tyDesc])
+
       # XXX: We can be extra clever here and call memset only
       # on the bytes following the m_type field?
       genObjectInit(p, cpsStmts, loc.t, loc, constructObj)

tests/cpp/t22680.nim

@@ -0,0 +1,50 @@
+discard """
+  cmd: "nim cpp $file"
+  output:'''
+cppNZ.x = 123
+cppNZInit.x = 123
+inheritCpp.x = 123
+inheritCppInit.x = 123
+inheritCppCtor.x = 123
+'''
+"""
+import std/sugar
+
+{.emit:"""/*TYPESECTION*/
+struct CppNonZero {
+  int x = 123;
+};
+""".}
+
+type
+  CppNonZero {.importcpp, inheritable.} = object
+    x: cint
+
+  InheritCpp = object of CppNonZero
+
+proc initCppNonZero: CppNonZero =
+  CppNonZero()
+
+proc initInheritCpp: InheritCpp =
+  InheritCpp()
+
+proc ctorInheritCpp: InheritCpp {.constructor.} =
+  discard
+
+proc main =
+  var cppNZ: CppNonZero
+  dump cppNZ.x
+
+  var cppNZInit = initCppNonZero()
+  dump cppNZInit.x
+
+  var inheritCpp: InheritCpp
+  dump inheritCpp.x
+
+  var inheritCppInit = initInheritCpp()
+  dump inheritCppInit.x
+
+  var inheritCppCtor = ctorInheritCpp()
+  dump inheritCppCtor.x
+
+main()