Merge pull request #1468 from Varriount/fix-1435

Fix 1435

compiler/ast.nim

@@ -1313,6 +1313,10 @@ proc newSons(father: PNode, length: int) =
     setLen(father.sons, length)
 
 proc skipTypes*(t: PType, kinds: TTypeKinds): PType =
+  ## Used throughout the compiler code to test whether a type tree contains or
+  ## doesn't contain a specific type/types - it is often the case that only the
+  ## last child nodes of a type tree need to be searched. This is a really hot
+  ## path within the compiler!
   result = t
   while result.kind in kinds: result = lastSon(result)
 

compiler/ccgtypes.nim

@@ -122,6 +122,7 @@ proc mapSetType(typ: PType): TCTypeKind =
   else: result = ctArray
 
 proc mapType(typ: PType): TCTypeKind = 
+  ## Maps a nimrod type to a C type
   case typ.kind
   of tyNone, tyStmt: result = ctVoid
   of tyBool: result = ctBool

compiler/semexprs.nim

@@ -199,6 +199,8 @@ proc isCastable(dst, src: PType): bool =
     result = (dstSize >= srcSize) or
         (skipTypes(dst, abstractInst).kind in IntegralTypes) or
         (skipTypes(src, abstractInst-{tyTypeDesc}).kind in IntegralTypes)
+  if result and src.kind == tyNil:
+    result = dst.size <= platform.ptrSize
   
 proc isSymChoice(n: PNode): bool {.inline.} =
   result = n.kind in nkSymChoices