fixes #9868

compiler/semfold.nim

@@ -626,6 +626,14 @@ proc getConstExpr(m: PSym, n: PNode; g: ModuleGraph): PNode =
         # It doesn't matter if the argument is const or not for mLengthArray.
         # This fixes bug #544.
         result = newIntNodeT(lengthOrd(g.config, n.sons[1].typ), n, g)
+      of mSizeOf:
+        let size = getSize(g.config, n[1].typ)
+        if size >= 0:
+          result = newIntNode(nkIntLit, size)
+          result.info = n.info
+          result.typ = getSysType(g, n.info, tyInt)
+        else:
+          result = nil
       of mAstToStr:
         result = newStrNodeT(renderTree(n[1], {renderNoComments}), n, g)
       of mConStrStr:

compiler/semmagic.nim

@@ -321,8 +321,6 @@ proc semOf(c: PContext, n: PNode): PNode =
 proc magicsAfterOverloadResolution(c: PContext, n: PNode,
                                    flags: TExprFlags): PNode =
   ## This is the preferred code point to implement magics.
-  ## This function basically works like a macro, with the difference
-  ## that it is implemented in the compiler and not on the nimvm.
   ## ``c`` the current module, a symbol table to a very good approximation
   ## ``n`` the ast like it would be passed to a real macro
   ## ``flags`` Some flags for more contextual information on how the

tests/misc/tsizeof2.nim

@@ -13,3 +13,5 @@ echo i
 # bug #9868
 proc foo(a: SomeInteger): array[sizeof(a), byte] =
   discard
+
+discard foo(1)