From 32d755beb8d83a666100ca9455df51b93caff1fc Mon Sep 17 00:00:00 2001
From: Julian <58199799+mov-rax@users.noreply.github.com>
Date: Mon, 3 Oct 2022 05:05:12 -0500
Subject: [PATCH] Sema: require reified packed struct fields to have zero
 alignment

---
 src/Sema.zig                                          |  4 ++++
 ...uct_field_alignment_unavailable_for_reify_type.zig | 11 +++++++++++
 2 files changed, 15 insertions(+)
 create mode 100644 test/cases/compile_errors/packed_struct_field_alignment_unavailable_for_reify_type.zig

diff --git a/src/Sema.zig b/src/Sema.zig
index aed09d6201..ed62fe02b2 100644
--- a/src/Sema.zig
+++ b/src/Sema.zig
@@ -17682,6 +17682,10 @@ fn reifyStruct(
         }
         const abi_align = @intCast(u29, (try alignment_val.getUnsignedIntAdvanced(target, sema.kit(block, src))).?);
 
+        if (layout == .Packed and abi_align != 0) {
+            return sema.fail(block, src, "alignment in a packed struct field must be set to 0", .{});
+        }
+
         const field_name = try name_val.toAllocatedBytes(
             Type.initTag(.const_slice_u8),
             new_decl_arena_allocator,
diff --git a/test/cases/compile_errors/packed_struct_field_alignment_unavailable_for_reify_type.zig b/test/cases/compile_errors/packed_struct_field_alignment_unavailable_for_reify_type.zig
new file mode 100644
index 0000000000..8c17e9100b
--- /dev/null
+++ b/test/cases/compile_errors/packed_struct_field_alignment_unavailable_for_reify_type.zig
@@ -0,0 +1,11 @@
+export fn entry() void {
+    _ = @Type(.{ .Struct = .{ .layout = .Packed, .fields = &.{
+        .{ .name = "one", .field_type = u4, .default_value = null, .is_comptime = false, .alignment = 2 },
+    }, .decls = &.{}, .is_tuple = false } });
+}
+
+// error
+// backend=stage2
+// target=native
+//
+// :2:9: error: alignment in a packed struct field must be set to 0