From f4ce27f29012cbaa3eafb8586fb27a6098acd873 Mon Sep 17 00:00:00 2001
From: Patrick McDermott <pj@pehjota.net>
Date: Wed, 01 Nov 2017 16:21:02 -0400
Subject: configure.ac: Enable many more warnings

---
(limited to 'configure.ac')

diff --git a/configure.ac b/configure.ac
index b15f168..6a65990 100644
--- a/configure.ac
+++ b/configure.ac
@@ -37,19 +37,31 @@ AX_CHECK_COMPILE_FLAG([-std=c11], [CFLAGS="${CFLAGS} -std=c11"], [
 	AX_CHECK_COMPILE_FLAG([-std=c1x], [CFLAGS="${CFLAGS} -std=c1x"], [], [])
 ], [])
 
-# Consider also:
-#   * -Wchkp
-#   * -Wformat=2
-#   * -Wnull-dereference
-#   * -Winit-self
-#   * -Wmissing-include-dirs
-#   * etc.
-# Cf. <https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html> and
-# <http://git.pehjota.net/overworld-rpg/overworld-rpg.git/tree/configure.ac#n60>
 AX_CFLAGS_WARN_ALL()  dnl Adds -Wall or equivalent
 AX_CHECK_COMPILE_FLAG([-Wpedantic], [AX_APPEND_FLAG([-Wpedantic])])
 AX_CHECK_COMPILE_FLAG([-Wextra],    [AX_APPEND_FLAG([-Wextra])])
 
+AC_ARG_ENABLE([gcc-warnings],
+	[AS_HELP_STRING([--enable-gcc-warnings], [turn on many GCC warnings])],
+	[case "${enableval}" in yes|no);; *) AC_MSG_ERROR(
+		[bad value ${enableval} for gcc-warnings option]);; esac],
+	[
+		gcc_warnings=no
+		gl_GCC_VERSION_IFELSE([4], [6],
+			[test -d "${srcdir}/.git" && gcc_warnings=yes])
+	]
+)
+if test "x${gcc_warnings}" = 'xyes'; then
+	nowarns=''
+	nowarns="${nowarns} -Wsystem-headers"
+	gl_MANYWARN_ALL_GCC([warns])
+	gl_MANYWARN_COMPLEMENT([warns], [${warns}], [${nowarns}])
+	for warn in ${warns}; do
+		gl_WARN_ADD([${warn}])
+	done
+	AC_SUBST([WARN_CFLAGS])
+fi
+
 AX_CHECK_COMPILE_FLAG([-fdiagnostics-color=auto],
 	[AX_APPEND_FLAG([-fdiagnostics-color=auto])])
 
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