add --experimental:vmopsDanger; add generic conversion for vmops (#13813)

* add --experimental:vmopsDanger; vmops cleanups

compiler/vmconv.nim

@@ -0,0 +1,41 @@
+import ast
+
+template elementType*(T: typedesc): typedesc =
+  typeof(block:
+    var a: T
+    for ai in a: ai)
+
+proc fromLit*(a: PNode, T: typedesc): auto =
+  ## generic PNode => type
+  ## see also reverse operation `toLit`
+  when T is set:
+    result = default(T)
+    type Ti = elementType(T)
+    for ai in a:
+      result.incl Ti(ai.intVal)
+  else:
+    static: doAssert false, "not yet supported: " & $T # add as needed
+
+proc toLit*[T](a: T): PNode =
+  ## generic type => PNode
+  ## see also reverse operation `fromLit`
+  when T is string: newStrNode(nkStrLit, a)
+  elif T is Ordinal: newIntNode(nkIntLit, a.ord)
+  elif T is (proc): newNode(nkNilLit)
+  elif T is ref:
+    if a == nil: newNode(nkNilLit)
+    else: toLit(a[])
+  elif T is tuple:
+    result = newTree(nkTupleConstr)
+    for ai in fields(a): result.add toLit(ai)
+  elif T is object:
+    result = newTree(nkObjConstr)
+    result.add(newNode(nkEmpty))
+    for k, ai in fieldPairs(a):
+      let reti = newNode(nkExprColonExpr)
+      reti.add k.toLit
+      reti.add ai.toLit
+      result.add reti
+  else:
+    static: doAssert false, "not yet supported: " & $T # add as needed
+