fixes #9868

compiler/semexprs.nim

@@ -1975,6 +1975,22 @@ proc setMs(n: PNode, s: PSym): PNode =
   n.sons[0] = newSymNode(s)
   n.sons[0].info = n.info
 
+proc semSizeof(c: PContext, n: PNode): PNode =
+  if sonsLen(n) != 2:
+    localError(c.config, n.info, errXExpectsTypeOrValue % "sizeof")
+  else:
+    n.sons[1] = semExprWithType(c, n.sons[1], {efDetermineType})
+    #restoreOldStyleType(n.sons[1])
+  n.typ = getSysType(c.graph, n.info, tyInt)
+
+  let size = getSize(c.config, n[1].typ)
+  if size >= 0:
+    result = newIntNode(nkIntLit, size)
+    result.info = n.info
+    result.typ = n.typ
+  else:
+    result = n
+
 proc semMagic(c: PContext, n: PNode, s: PSym, flags: TExprFlags): PNode =
   # this is a hotspot in the compiler!
   result = n
@@ -2060,6 +2076,7 @@ proc semMagic(c: PContext, n: PNode, s: PSym, flags: TExprFlags): PNode =
       result = setMs(n, s)
     else:
       result = c.graph.emptyNode
+  of mSizeOf: result = semSizeof(c, setMs(n, s))
   of mOmpParFor:
     checkMinSonsLen(n, 3, c.config)
     result = semDirectOp(c, n, flags)

compiler/sizealignoffsetimpl.nim

@@ -52,6 +52,7 @@ proc computeSubObjectAlign(conf: ConfigRef; n: PNode): BiggestInt =
 proc computeObjectOffsetsFoldFunction(conf: ConfigRef; n: PNode, initialOffset: BiggestInt): tuple[offset, align: BiggestInt] =
   ## ``offset`` is the offset within the object, after the node has been written, no padding bytes added
   ## ``align`` maximum alignment from all sub nodes
+  assert n != nil
   if n.typ != nil and n.typ.size == szIllegalRecursion:
     result.offset = szIllegalRecursion
     result.align  = szIllegalRecursion
@@ -177,7 +178,7 @@ proc computePackedObjectOffsetsFoldFunction(conf: ConfigRef; n: PNode, initialOf
 
 proc computeSizeAlign(conf: ConfigRef; typ: PType) =
   ## computes and sets ``size`` and ``align`` members of ``typ``
-
+  assert typ != nil
   let hasSize = typ.size != szUncomputedSize
   let hasAlign = typ.align != szUncomputedSize
 

tests/misc/tsizeof2.nim

@@ -9,3 +9,7 @@ type
 const i = sizeof(MyStruct)
 
 echo i
+
+# bug #9868
+proc foo(a: SomeInteger): array[sizeof(a), byte] =
+  discard