From 25a3fc8526cfe7300235108f777f33f00af2a811 Mon Sep 17 00:00:00 2001
From: Hugo Hurskainen <hugo.hurskainen@gmail.com>
Date: Sun, 14 Jun 2026 13:53:30 +0300
Subject: [PATCH] build: enforce C11 as minimum compiler standard

Replace obsolete AC_PROG_CC_C99 with AC_PROG_CC (which auto-selects the
newest available standard: C17 on GCC 8+, C11 on GCC 4.9-7) and add an
AC_COMPILE_IFELSE gate that aborts configure if __STDC_VERSION__ < 201112L.
Makes C11 or newer a hard build requirement in line with the project coding
guidelines ("C11 recommended, C99 acceptable") and enables use of _Static_assert,
_Noreturn, and inline functions without preprocessor guards.
---
 configure.ac | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/configure.ac b/configure.ac
index f28d2b28..cfcdb89d 100644
--- a/configure.ac
+++ b/configure.ac
@@ -44,9 +44,21 @@ AC_CANONICAL_HOST
 AC_CANONICAL_BUILD
 AC_CANONICAL_TARGET
 AM_INIT_AUTOMAKE([-Wall -Werror foreign subdir-objects])
+
 AC_PROG_CC
 AC_USE_SYSTEM_EXTENSIONS
-AC_PROG_CC_C99
+dnl
+dnl Check that compiler supports C11 or newer standard
+dnl
+AC_COMPILE_IFELSE(
+  [AC_LANG_PROGRAM([[
+    #if !defined(__STDC_VERSION__) || __STDC_VERSION__ < 201112L
+    # error C11 or newer required
+    #endif
+  ]])],
+  [],
+  [AC_MSG_ERROR([C11 or newer compiler required (GCC >= 4.9, Clang >= 3.3)])]
+)
 AM_PROG_CC_C_O
 AM_PROG_AR
 AC_PROG_LIBTOOL