Add C11 compiler detection (optional) and <stdatomic.h> detection

.github/workflows/dev.yml

@@ -242,19 +242,33 @@ jobs:
           maint/RunSymbolTest install-dir/usr/local/lib/ maint/
 
   passenger:
-    # Tests with: Autoconf on oldest RHEL (in extended support).
-    # That's the absolute limit to how old a Linux version I'll tolerate regular testing on.
-    name: GCC, very old Autotools
+    # Tests on the oldest RHEL release in extended support with the minimum
+    # supported Autoconf version.
+    name: GCC, RHEL 8, minimum Autoconf
     runs-on: ubuntu-latest
     container: redhat/ubi8:8.6
     if: github.event_name != 'workflow_dispatch' || (inputs.job_id == 'all' || inputs.job_id == 'passenger')
     steps:
       - name: Setup
         run: |
           yum -q makecache
-          yum -q install -y gcc git make automake autoconf libtool diffutils file glibc-langpack-en
+          yum -q install -y gcc git make automake libtool diffutils file glibc-langpack-en m4 perl curl xz
           yum -q update -y glibc-common
 
+      - name: Install Autoconf 2.71
+        run: |
+          curl --fail --location --retry 3 --output "$RUNNER_TEMP/autoconf-2.71.tar.xz" \
+            https://ftp.gnu.org/gnu/autoconf/autoconf-2.71.tar.xz
+          printf '%s  %s\n' \
+            f14c83cfebcc9427f2c3cea7258bd90df972d92eb26752da4ddad81c87a0faa4 \
+            "$RUNNER_TEMP/autoconf-2.71.tar.xz" | sha256sum --check --status
+          tar -C "$RUNNER_TEMP" -xf "$RUNNER_TEMP/autoconf-2.71.tar.xz"
+          pushd "$RUNNER_TEMP/autoconf-2.71"
+          ./configure --prefix="$RUNNER_TEMP/autoconf-prefix"
+          make -j"$(nproc)" install
+          popd
+          echo "$RUNNER_TEMP/autoconf-prefix/bin" >> "$GITHUB_PATH"
+
       - name: Checkout
         uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
         with:

BUILD.bazel

@@ -27,7 +27,7 @@ LOCAL_DEFINES = [
     "SUPPORT_UNICODE",
 ] + select({
     "@platforms//os:windows": [],
-    "//conditions:default": ["HAVE_UNISTD_H"],
+    "//conditions:default": ["HAVE_UNISTD_H", "HAVE_STDATOMIC_H"],
 })
 
 # Workaround for a Bazel quirk. It is extremely strict about the #include path

CMakeLists.txt

@@ -110,7 +110,13 @@ message(STATUS "Using CMake version ${CMAKE_VERSION} (${CMAKE_COMMAND})")
 # Increased minimum to 3.15 to allow use of string(REPEAT).
 cmake_minimum_required(VERSION 3.15 FATAL_ERROR)
 project(PCRE2 C)
-set(CMAKE_C_STANDARD 99)
+if("c_std_11" IN_LIST CMAKE_C_COMPILE_FEATURES)
+  set(CMAKE_C_STANDARD 11)
+elseif("c_std_99" IN_LIST CMAKE_C_COMPILE_FEATURES)
+  set(CMAKE_C_STANDARD 99)
+else()
+  message(FATAL_ERROR "C compiler must support at least C99.")
+endif()
 set(CMAKE_C_STANDARD_REQUIRED TRUE)
 set(CMAKE_C_VISIBILITY_PRESET hidden)
 
@@ -190,11 +196,26 @@ check_symbol_exists(secure_getenv "stdlib.h" HAVE_SECURE_GETENV) # glibc 2.17
 check_symbol_exists(setrlimit "sys/resource.h" HAVE_SETRLIMIT)
 cmake_pop_check_state()
 
+check_c_source_compiles(
+  [=[
+  #ifdef __STDC_NO_ATOMICS__
+  #error "C compiler does not support standard C atomics"
+  #endif
+  #include <stdatomic.h>
+  int main(void) {
+    atomic_int value;
+    atomic_init(&value, 0);
+    return atomic_load(&value);
+  }
+  ]=]
+  HAVE_STDATOMIC_H
+)
+
 check_c_source_compiles(
   [=[
   #include <stdlib.h>
   #include <limits.h>
-  int main(int c, char *v[]) { char buf[PATH_MAX]; realpath(v[c], buf); return 0; }
+  int main(int c, char *v[]) { char buf[PATH_MAX]; return realpath(v[c], buf) == NULL; }
   ]=]
   HAVE_REALPATH
 )

build.zig

@@ -60,9 +60,14 @@ pub fn build(b: *std.Build) !void {
     const is_glibc = rt.isGnuLibC();
     const is_freebsd = rt.isFreeBSDLibC();
 
-    const cflags = &.{
+    const common_cflags: []const []const u8 = &.{
+        "-std=c11",
         "-fvisibility=hidden",
     };
+    const cflags: []const []const u8 = if (rt.os.tag == .linux)
+        try std.mem.concat(b.allocator, []const u8, &.{ common_cflags, &.{"-D_GNU_SOURCE"} })
+    else
+        common_cflags;
 
     const config_h = b.addConfigHeader(
         .{
@@ -82,6 +87,7 @@ pub fn build(b: *std.Build) !void {
             .HAVE_SYS_TYPES_H = true,
             .HAVE_UNISTD_H = is_unix or is_mingw,
             .HAVE_WINDOWS_H = rt.os.tag == .windows,
+            .HAVE_STDATOMIC_H = true,
 
             .HAVE_MEMFD_CREATE = is_musl or is_glibc or is_freebsd,
             .HAVE_SECURE_GETENV = is_musl or is_glibc or is_freebsd,