From 9193c85b614530dfb0c34fe7afc11d70e8faa1d1 Mon Sep 17 00:00:00 2001
From: cooldome <ariabushenko@gmail.com>
Date: Thu, 8 Oct 2020 08:12:03 +0100
Subject: [PATCH] fix #15516 (#15518)

(cherry picked from commit fe187719abf5fa87e12e4092f87c270234fad25c)
---
 compiler/sizealignoffsetimpl.nim | 10 ++++++----
 tests/misc/tsizeof.nim           | 19 +++++++++++++++++--
 2 files changed, 23 insertions(+), 6 deletions(-)

diff --git a/compiler/sizealignoffsetimpl.nim b/compiler/sizealignoffsetimpl.nim
index 1692aaf64c..5cd2f8c3fb 100644
--- a/compiler/sizealignoffsetimpl.nim
+++ b/compiler/sizealignoffsetimpl.nim
@@ -138,12 +138,13 @@ proc computeObjectOffsetsFoldFunction(conf: ConfigRef; n: PNode, packed: bool, a
       accum.offset  = szUnknownSize
       accum.maxAlign = szUnknownSize
     else:
-      # the union neds to be aligned first, before the offsets can be assigned
+      # the union needs to be aligned first, before the offsets can be assigned
       accum.align(maxChildAlign)
       let accumRoot = accum # copy, because each branch should start af the same offset
       for i in 1 ..< len(n):
-        var branchAccum = accumRoot
+        var branchAccum = OffsetAccum(offset: accumRoot.offset, maxAlign: 1)
         computeObjectOffsetsFoldFunction(conf, n.sons[i].lastSon, packed, branchAccum)
+        discard finish(branchAccum)
         accum.mergeBranch(branchAccum)
   of nkRecList:
     for i, child in n.sons:
@@ -171,9 +172,10 @@ proc computeUnionObjectOffsetsFoldFunction(conf: ConfigRef; n: PNode; accum: var
     localError(conf, n.info, "Illegal use of ``case`` in union type.")
   of nkRecList:
     let accumRoot = accum # copy, because each branch should start af the same offset
-    for i, child in n.sons:
-      var branchAccum = accumRoot
+    for child in n.sons:
+      var branchAccum = OffsetAccum(offset: accumRoot.offset, maxAlign: 1)
       computeUnionObjectOffsetsFoldFunction(conf, child, branchAccum)
+      discard finish(branchAccum)
       accum.mergeBranch(branchAccum)
   of nkSym:
     var size = szUnknownSize
diff --git a/tests/misc/tsizeof.nim b/tests/misc/tsizeof.nim
index a4633021b2..89dd669027 100644
--- a/tests/misc/tsizeof.nim
+++ b/tests/misc/tsizeof.nim
@@ -336,6 +336,21 @@ testinstance:
       a: int32
       b: T
 
+    Kind = enum
+      K1, K2
+
+    AnotherEnum = enum
+      X1, X2, X3
+
+    MyObject = object
+      s: string
+      case k: Kind
+      of K1: nil
+      of K2:
+          x: float
+          y: int32
+      z: AnotherEnum
+
   const trivialSize = sizeof(TrivialType) # needs to be able to evaluate at compile time
 
   proc main(): void =
@@ -350,6 +365,7 @@ testinstance:
     var ro : RootObj
     var go : GenericObject[int64]
     var po : PaddingOfSetEnum33
+    var issue15516: MyObject
 
     var
       e1: Enum1
@@ -368,8 +384,7 @@ testinstance:
     else:
       doAssert sizeof(SimpleAlignment) > 10
 
-    testSizeAlignOf(t,a,b,c,d,e,f,g,ro,go,po, e1, e2, e4, e8, eoa, eob)
-
+    testSizeAlignOf(t,a,b,c,d,e,f,g,ro,go,po, e1, e2, e4, e8, eoa, eob, issue15516)
 
     type
       WithBitsize {.objectconfig.} = object