From 3b7af398a989e876b1e7afb48d6b6a81fcfcb7c9 Mon Sep 17 00:00:00 2001
From: acqn <acqn163@outlook.com>
Date: Wed, 15 Nov 2023 21:32:24 +0800
Subject: [PATCH] Fixed initialization of union when it has an anonymous
 bit-field as the first member declaration.

---
 src/cc65/initdata.c       | 38 ++++++++++++++++++++------------------
 test/val/bitfield-union.c |  9 +++++++--
 2 files changed, 27 insertions(+), 20 deletions(-)

diff --git a/src/cc65/initdata.c b/src/cc65/initdata.c
index e9442737c..5401e577c 100644
--- a/src/cc65/initdata.c
+++ b/src/cc65/initdata.c
@@ -511,18 +511,20 @@ static unsigned ParseStructInit (Type* T, int* Braces, int AllowFlexibleMembers)
         /* This may be an anonymous bit-field, in which case it doesn't
         ** have an initializer.
         */
-        if (SymIsBitField (TagSym) && (IsAnonName (TagSym->Name))) {
-            /* Account for the data and output it if we have at least a full
-            ** byte. We may have more if there was storage unit overlap, for
-            ** example two consecutive 7 bit fields. Those would be packed
-            ** into 2 bytes.
-            */
-            SI.ValBits += TagSym->Type->A.B.Width;
-            CHECK (SI.ValBits <= CHAR_BIT * sizeof(SI.BitVal));
-            /* TODO: Generalize this so any type can be used. */
-            CHECK (SI.ValBits <= LONG_BITS);
-            while (SI.ValBits >= CHAR_BITS) {
-                DefineBitFieldData (&SI);
+        if (SymIsBitField (TagSym) && IsAnonName (TagSym->Name)) {
+            if (!IsTypeUnion (T)) {
+                /* Account for the data and output it if we have at least a full
+                ** byte. We may have more if there was storage unit overlap, for
+                ** example two consecutive 7 bit fields. Those would be packed
+                ** into 2 bytes.
+                */
+                SI.ValBits += TagSym->Type->A.B.Width;
+                CHECK (SI.ValBits <= CHAR_BIT * sizeof(SI.BitVal));
+                /* TODO: Generalize this so any type can be used. */
+                CHECK (SI.ValBits <= LONG_BITS);
+                while (SI.ValBits >= CHAR_BITS) {
+                    DefineBitFieldData (&SI);
+                }
             }
             /* Avoid consuming the comma if any */
             goto NextMember;
@@ -628,15 +630,15 @@ static unsigned ParseStructInit (Type* T, int* Braces, int AllowFlexibleMembers)
         /* Skip the comma next round */
         SkipComma = 1;
 
-NextMember:
-        /* Next member. For unions, only the first one can be initialized */
+        /* For unions, only the first named member can be initialized */
         if (IsTypeUnion (T)) {
-            /* Union */
             TagSym = 0;
-        } else {
-            /* Struct */
-            TagSym = TagSym->NextSym;
+            continue;
         }
+
+NextMember:
+        /* Next member */
+        TagSym = TagSym->NextSym;
     }
 
     if (HasCurly) {
diff --git a/test/val/bitfield-union.c b/test/val/bitfield-union.c
index 1fd201456..4c01d2183 100644
--- a/test/val/bitfield-union.c
+++ b/test/val/bitfield-union.c
@@ -1,5 +1,5 @@
 /*
-  Copyright 2020 The cc65 Authors
+  Copyright 2020-2023 The cc65 Authors
 
   This software is provided 'as-is', without any express or implied
   warranty. In no event will the authors be held liable for any damages
@@ -25,6 +25,7 @@
 #include <stdio.h>
 
 typedef union {
+     const unsigned int : 1;
      unsigned int bf;
 
      struct {
@@ -38,8 +39,12 @@ static unsigned char failures = 0;
 
 int main (void)
 {
-     bitfield_t bitfield = {0};
+     bitfield_t bitfield = { 42 };
 
+     printf ("Bitfield: %u\n", bitfield.bf);
+     if (bitfield.bf != 42) failures++;
+
+     bitfield.bf ^= 42;
      printf ("Bitfield: %u\n", bitfield.bf);
      if (bitfield.bf != 0) failures++;