fixes #12488 [backport]

compiler/vmgen.nim

@@ -2129,6 +2129,9 @@ proc gen(c: PCtx; n: PNode; dest: var TDest; flags: TGenFlags = {}) =
     genTypeLit(c, n.typ, dest)
   of nkComesFrom:
     discard "XXX to implement for better stack traces"
+  else:
+    if n.typ != nil and n.typ.isCompileTimeOnly:
+      genTypeLit(c, n.typ, dest)
     else:
       globalError(c.config, n.info, "cannot generate VM code for " & $n)
 

tests/vm/tmisc_vm.nim

@@ -15,6 +15,9 @@ Done!
 foo4
 foo4
 foo4
+(a: 0, b: 0)
+(a: 0, b: 0)
+(a: 0, b: 0)
 '''
 """
 
@@ -234,3 +237,17 @@ static:
   echo foo()
   echo foo()
   echo foo()
+
+# bug #12488
+type
+  MyObject = object
+    a,b: int
+  MyObjectRef = ref MyObject
+
+static:
+  let x1 = new(MyObject)
+  echo x1[]
+  let x2 = new(MyObjectRef)
+  echo x2[]
+  let x3 = new(ref MyObject) # cannot generate VM code for ref MyObject
+  echo x3[]