From 1c70056c20ad0001b45daa7289c01d0eb3577211 Mon Sep 17 00:00:00 2001
From: Kaz Kylheku <kaz@kylheku.com>
Date: Fri, 20 May 2022 06:34:34 -0700
Subject: ffi: pack: implement documented align transformation.

* ffi.c (ffi_pack_members): Static function removed.
(ffi_transform_pack): New static function.
(ffi_type_compile): Rely on ffi_transform_pack to recognize
and perform all necessary transformations.
Cosmetic issue: when a struct is compiled, and the individual
member types undergo transformation during member compilation,
the syntax for the struct is nevertheless the original one
with the untransformed members.
---
 ffi.c | 51 ++++++++++++++++++++++++++++++++-------------------
 1 file changed, 32 insertions(+), 19 deletions(-)

diff --git a/ffi.c b/ffi.c
index 437713d7..e0276ec7 100644
--- a/ffi.c
+++ b/ffi.c
@@ -3923,26 +3923,41 @@ static val ffi_struct_init(val slot_init, val strct)
   return nil;
 }
 
-static val ffi_pack_members(val struct_syntax, val align)
+static val ffi_transform_pack(val syntax, val align)
 {
-  val op = pop(&struct_syntax);
-  val name = pop(&struct_syntax);
-  val iter;
-  list_collect_decl (packed, ptail);
+  val op = pop(&syntax);
 
-  for (iter = struct_syntax; iter; iter = cdr(iter)) {
-    val slot_spec = car(iter);
-    val slot = car(slot_spec);
-    val type = cadr(slot_spec);
-    val init = caddr(slot_spec);
-    val packed_type = list(pack_s, align, type, nao);
+  if (op == struct_s || op == union_s)
+  {
+    val name = pop(&syntax);
+    val iter;
+    list_collect_decl (packed, ptail);
+
+    for (iter = syntax; iter; iter = cdr(iter)) {
+      val slot_spec = car(iter);
+      val slot = car(slot_spec);
+      val type = cadr(slot_spec);
+      val init = caddr(slot_spec);
+      val packed_type = list(pack_s, align, type, nao);
+
+      ptail = list_collect(ptail, if3(init,
+                                      list(slot, packed_type, init, nao),
+                                      list(slot, packed_type, nao)));
+    }
 
-    ptail = list_collect(ptail, if3(init,
-                                    list(slot, packed_type, init, nao),
-                                    list(slot, packed_type, nao)));
+    return cons(op, cons(name, packed));
+  } else if (op == align_s) {
+    if (length(syntax) == one) {
+      val type = car(syntax);
+      return list(align_s, list(pack_s, align, type, nao), nao);
+    } else if (length(syntax) == two) {
+      val align = car(syntax);
+      val type = cadr(syntax);
+      return list(align_s, align, list(pack_s, align, type, nao), nao);
+    }
   }
 
-  return cons(op, cons(name, packed));
+  return syntax;
 }
 
 val ffi_type_compile(val syntax)
@@ -4334,10 +4349,8 @@ val ffi_type_compile(val syntax)
                   self, nao);
       } else {
         val alsyntax = if3(twoarg, cadr(syntax), caddr(syntax));
-        val xalsyntax = if3(sym == pack_s && consp(alsyntax) &&
-                            (car(alsyntax) == struct_s ||
-                             car(alsyntax) == union_s),
-                            ffi_pack_members(alsyntax, align),
+        val xalsyntax = if3(sym == pack_s && consp(alsyntax),
+                            ffi_transform_pack(alsyntax, align),
                             alsyntax);
         val altype = ffi_type_compile(xalsyntax);
         if (xalsyntax != alsyntax) {
-- 
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