added typetraits.supportsCopyMem

compiler/semmagic.nim

@@ -146,8 +146,13 @@ proc evalTypeTrait(traitCall: PNode, operand: PType, context: PSym): PNode =
     result = res.base.toNode(traitCall.info)
   of "stripGenericParams":
     result = uninstantiate(operand).toNode(traitCall.info)
+  of "supportsCopyMem":
+    let complexObj = containsGarbageCollectedRef(operand) or
+                     hasDestructor(operand)
+    result = newIntNodeT(ord(not complexObj), traitCall)
   else:
-    internalAssert false
+    localError(traitCall.info, "unknown trait")
+    result = emptyNode
 
 proc semTypeTraits(c: PContext, n: PNode): PNode =
   checkMinSonsLen(n, 2)

lib/pure/typetraits.nim

@@ -49,3 +49,6 @@ proc stripGenericParams*(t: typedesc): typedesc {.magic: "TypeTrait".}
   ## This trait is similar to `genericHead`, but instead of producing
   ## error for non-generic types, it will just return them unmodified
 
+proc supportsCopyMem*(t: typedesc): bool {.magic: "TypeTrait".}
+  ## This trait returns true iff the type ``t`` is safe to use for
+  ## `copyMem`:idx:. Other languages name a type like these `blob`:idx:.