From ab0562950c36af3040b48ab4e8494da97505677c Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Motiejus=20Jak=C5=A1tys?= <motiejus@jakstys.lt>
Date: Mon, 21 Feb 2022 13:53:52 +0200
Subject: [PATCH] add some guard rails w.r.t. padding

---
 src/user.zig | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/src/user.zig b/src/user.zig
index 47b3241..387fdf5 100644
--- a/src/user.zig
+++ b/src/user.zig
@@ -199,8 +199,19 @@ pub const UserReader = struct {
 
 const testing = std.testing;
 
-test "PackedUser is byte-aligned" {
+test "PackedUser alignment" {
+    // byte-aligned
     try testing.expectEqual(0, @rem(@bitSizeOf(PackedUser), 8));
+
+    const bytes = @divExact(@bitSizeOf(PackedUser), 8);
+
+    // External padding (PackedUserAlignmentBits) must be higher or equal to
+    // the "internal" PackedUser alignment. By aligning PackedUser we are also
+    // working around https://github.com/ziglang/zig/issues/10958 ; PackedUser
+    // cannot be converted from/to [@bitSizeOf(PackedUser)/8]u8;
+    // asBytes/bytesAsValue use @sizeOf, which is larger. Now we are putting no
+    // more than 1, but it probably could be higher.
+    try testing.expect(@sizeOf(PackedUser) - bytes <= 1);
 }
 
 fn testShellIndex(shell: []const u8) ?u6 {