From 23c46e045a2a44331aafd3245d82c4fb216044b9 Mon Sep 17 00:00:00 2001
From: Michael Forney <mforney@mforney.org>
Date: Sat, 2 May 2026 20:10:48 -0700
Subject: [PATCH] Add C23 attribute support

---
 pngconf.h  | 25 +++++++++++++++++++++++--
 pngerror.c |  8 ++++----
 pngpriv.h  |  6 +++---
 3 files changed, 30 insertions(+), 9 deletions(-)

diff --git a/pngconf.h b/pngconf.h
index 000d7b1a8..16d290ccd 100644
--- a/pngconf.h
+++ b/pngconf.h
@@ -299,7 +299,7 @@
 #ifndef PNG_EXPORTA
 #  define PNG_EXPORTA(ordinal, type, name, args, attributes) \
       PNG_FUNCTION(PNG_EXPORT_TYPE(type), (PNGAPI name), PNGARG(args), \
-      PNG_LINKAGE_API attributes)
+      attributes PNG_LINKAGE_API)
 #endif
 
 /* ANSI-C (C90) does not permit a macro to be invoked with an empty argument,
@@ -339,7 +339,28 @@
    * version 1.2.41.  Disabling these removes the warnings but may also produce
    * less efficient code.
    */
-#  if defined(__clang__) && defined(__has_attribute)
+#  if defined(__STDC_VERSION__) && __STDC_VERSION__ >= 202311L
+#    if !defined(PNG_USE_RESULT)
+#      define PNG_USE_RESULT [[nodiscard]]
+#    endif
+#    if !defined(PNG_NORETURN) && __has_attribute(__noreturn__)
+#      define PNG_NORETURN [[noreturn]]
+#    endif
+#    if !defined(PNG_ALLOCATED) && defined(__has_c_attribute) && __has_c_attribute(gnu::malloc)
+#      define PNG_ALLOCATED [[gnu::malloc]]
+#    endif
+#    if !defined(PNG_DEPRECATED) && __has_attribute(__deprecated__)
+#      define PNG_DEPRECATED [[deprecated]]
+#    endif
+#    if !defined(PNG_PRIVATE) && defined(__has_c_attribute) && __has_c_attribute(gnu::unavailable)
+#      define PNG_PRIVATE [[gnu::unavailable(\
+             "This function is not exported by libpng.")]]
+#    endif
+#    ifndef PNG_RESTRICT
+#      define PNG_RESTRICT restrict
+#    endif
+
+#  elif defined(__clang__) && defined(__has_attribute)
    /* Clang defines both __clang__ and __GNUC__. Check __clang__ first. */
 #    if !defined(PNG_USE_RESULT) && __has_attribute(__warn_unused_result__)
 #      define PNG_USE_RESULT __attribute__((__warn_unused_result__))
diff --git a/pngerror.c b/pngerror.c
index 29ebda794..4bab0a63c 100644
--- a/pngerror.c
+++ b/pngerror.c
@@ -20,8 +20,8 @@
 
 #if defined(PNG_READ_SUPPORTED) || defined(PNG_WRITE_SUPPORTED)
 
-static PNG_FUNCTION(void, png_default_error,PNGARG((png_const_structrp png_ptr,
-    png_const_charp error_message)),PNG_NORETURN);
+PNG_FUNCTION(void, png_default_error,PNGARG((png_const_structrp png_ptr,
+    png_const_charp error_message)),PNG_NORETURN static);
 
 #ifdef PNG_WARNINGS_SUPPORTED
 static void /* PRIVATE */
@@ -707,9 +707,9 @@ png_free_jmpbuf(png_structrp png_ptr)
  * function is used by default, or if the program supplies NULL for the
  * error function pointer in png_set_error_fn().
  */
-static PNG_FUNCTION(void /* PRIVATE */,
+PNG_FUNCTION(void /* PRIVATE */,
 png_default_error,(png_const_structrp png_ptr, png_const_charp error_message),
-    PNG_NORETURN)
+    PNG_NORETURN static)
 {
 #ifdef PNG_CONSOLE_IO_SUPPORTED
 #ifdef PNG_ERROR_NUMBERS_SUPPORTED
diff --git a/pngpriv.h b/pngpriv.h
index 9bfdb7134..2dcf50c7b 100644
--- a/pngpriv.h
+++ b/pngpriv.h
@@ -396,13 +396,13 @@
 
 #ifndef PNG_INTERNAL_FUNCTION
 #  define PNG_INTERNAL_FUNCTION(type, name, args, attributes)\
-      PNG_LINKAGE_FUNCTION PNG_FUNCTION(type, name, args, PNG_EMPTY attributes)
+      PNG_FUNCTION(type, name, args, attributes PNG_LINKAGE_FUNCTION)
 #endif
 
 #ifndef PNG_INTERNAL_CALLBACK
 #  define PNG_INTERNAL_CALLBACK(type, name, args, attributes)\
-      PNG_LINKAGE_CALLBACK PNG_FUNCTION(type, (PNGCBAPI name), args,\
-         PNG_EMPTY attributes)
+      PNG_FUNCTION(type, (PNGCBAPI name), args,\
+         attributes PNG_LINKAGE_CALLBACK)
 #endif
 
 /* If floating or fixed point APIs are disabled they may still be compiled
-- 
2.49.0