build: move warning checks to configure

This allows us to only add the warning flag if the compiler supports it,
improving the compatibility with clang.

Author: lucasdemarchi

Makefile.am

@@ -45,82 +45,21 @@ AM_CPPFLAGS = \
 
 AM_CFLAGS = \
 	-pipe \
-	-Wall \
-	-W \
-	-Wextra \
-	-Wno-inline \
-	-Wundef \
-	-Wformat=2 \
-	-Wlogical-op \
-	-Wsign-compare \
-	-Wformat-security \
-	-Wmissing-include-dirs \
-	-Wformat-nonliteral \
-	-Wold-style-definition \
-	-Wpointer-arith \
-	-Winit-self \
-	-Wdeclaration-after-statement \
-	-Wfloat-equal \
-	-Wmissing-prototypes \
-	-Wstrict-prototypes \
-	-Wredundant-decls \
-	-Wmissing-declarations \
-	-Wmissing-noreturn \
-	-Wshadow \
-	-Wendif-labels \
-	-Wstrict-aliasing=3 \
-	-Wwrite-strings \
-	-Wno-long-long \
-	-Wno-overlength-strings \
-	-Wno-unused-parameter \
-	-Wno-missing-field-initializers \
-	-Wno-unused-result \
-	-Wnested-externs \
-	-Wchar-subscripts \
-	-Wtype-limits \
-	-Wuninitialized \
 	-fno-common \
 	-fdiagnostics-show-option \
 	-fvisibility=hidden \
 	-ffunction-sections \
-	-fdata-sections
+	-fdata-sections \
+	$(OUR_CFLAGS)
 
 AM_CXXFLAGS = \
 	-pipe \
-	-Wall \
-	-W \
-	-Wextra \
-	-Wno-inline \
-	-Wundef \
-	-Wformat=2 \
-	-Wlogical-op \
-	-Wsign-compare \
-	-Wformat-security \
-	-Wmissing-include-dirs \
-	-Wformat-nonliteral \
-	-Wpointer-arith \
-	-Winit-self \
-	-Wfloat-equal \
-	-Wredundant-decls \
-	-Wmissing-declarations \
-	-Wmissing-noreturn \
-	-Wshadow \
-	-Wendif-labels \
-	-Wstrict-aliasing=3 \
-	-Wwrite-strings \
-	-Wno-long-long \
-	-Wno-overlength-strings \
-	-Wno-unused-parameter \
-	-Wno-missing-field-initializers \
-	-Wno-unused-result \
-	-Wchar-subscripts \
-	-Wtype-limits \
-	-Wuninitialized \
 	-fno-common \
 	-fdiagnostics-show-option \
 	-fvisibility=hidden \
 	-ffunction-sections \
-	-fdata-sections
+	-fdata-sections \
+	$(OUR_CXXFLAGS)
 
 AM_LDFLAGS = \
 	-Wl,--as-needed \

configure.ac

@@ -95,6 +95,81 @@ AM_CONDITIONAL(SYSTEMD, test "${enable_systemd}" != "no")
 # Default CFLAGS and LDFLAGS
 #####################################################################
 
+# Check C compiler flag
+AC_LANG_PUSH([C])
+CC_CHECK_FLAGS_APPEND(with_cflags, [CFLAGS], [ \
+	-Wall \
+	-W \
+	-Wextra \
+	-Wno-inline \
+	-Wundef \
+	-Wformat=2 \
+	-Wlogical-op \
+	-Wsign-compare \
+	-Wformat-security \
+	-Wmissing-include-dirs \
+	-Wformat-nonliteral \
+	-Wold-style-definition \
+	-Wpointer-arith \
+	-Winit-self \
+	-Wdeclaration-after-statement \
+	-Wfloat-equal \
+	-Wmissing-prototypes \
+	-Wstrict-prototypes \
+	-Wredundant-decls \
+	-Wmissing-declarations \
+	-Wmissing-noreturn \
+	-Wshadow \
+	-Wendif-labels \
+	-Wstrict-aliasing=3 \
+	-Wwrite-strings \
+	-Wno-long-long \
+	-Wno-overlength-strings \
+	-Wno-unused-parameter \
+	-Wno-missing-field-initializers \
+	-Wno-unused-result \
+	-Wnested-externs \
+	-Wchar-subscripts \
+	-Wtype-limits \
+	-Wuninitialized])
+AC_SUBST([OUR_CFLAGS], "$with_cflags")
+AC_LANG_POP([C])
+
+# Check C++ compiler flags
+AC_LANG_PUSH([C++])
+CC_CHECK_FLAGS_APPEND(with_cxxflags, [CXXFLAGS], [ \
+	-Wall \
+	-W \
+	-Wextra \
+	-Wno-inline \
+	-Wundef \
+	-Wformat=2 \
+	-Wlogical-op \
+	-Wsign-compare \
+	-Wformat-security \
+	-Wmissing-include-dirs \
+	-Wformat-nonliteral \
+	-Wpointer-arith \
+	-Winit-self \
+	-Wfloat-equal \
+	-Wredundant-decls \
+	-Wmissing-declarations \
+	-Wmissing-noreturn \
+	-Wshadow \
+	-Wendif-labels \
+	-Wstrict-aliasing=3 \
+	-Wwrite-strings \
+	-Wno-long-long \
+	-Wno-overlength-strings \
+	-Wno-unused-parameter \
+	-Wno-missing-field-initializers \
+	-Wno-unused-result \
+	-Wchar-subscripts \
+	-Wtype-limits \
+	-Wuninitialized])
+AC_LANG_POP([C++])
+AC_SUBST([OUR_CXXFLAGS], "$with_cxxflags")
+
 #####################################################################
 # Generate files from *.in
 #####################################################################

m4/ax_check_compile_flag.m4

@@ -0,0 +1,53 @@
+# ===========================================================================
+#  https://www.gnu.org/software/autoconf-archive/ax_check_compile_flag.html
+# ===========================================================================
+#
+# SYNOPSIS
+#
+#   AX_CHECK_COMPILE_FLAG(FLAG, [ACTION-SUCCESS], [ACTION-FAILURE], [EXTRA-FLAGS], [INPUT])
+#
+# DESCRIPTION
+#
+#   Check whether the given FLAG works with the current language's compiler
+#   or gives an error.  (Warnings, however, are ignored)
+#
+#   ACTION-SUCCESS/ACTION-FAILURE are shell commands to execute on
+#   success/failure.
+#
+#   If EXTRA-FLAGS is defined, it is added to the current language's default
+#   flags (e.g. CFLAGS) when the check is done.  The check is thus made with
+#   the flags: "CFLAGS EXTRA-FLAGS FLAG".  This can for example be used to
+#   force the compiler to issue an error when a bad flag is given.
+#
+#   INPUT gives an alternative input source to AC_COMPILE_IFELSE.
+#
+#   NOTE: Implementation based on AX_CFLAGS_GCC_OPTION. Please keep this
+#   macro in sync with AX_CHECK_{PREPROC,LINK}_FLAG.
+#
+# LICENSE
+#
+#   Copyright (c) 2008 Guido U. Draheim <[email protected]>
+#   Copyright (c) 2011 Maarten Bosmans <[email protected]>
+#
+#   Copying and distribution of this file, with or without modification, are
+#   permitted in any medium without royalty provided the copyright notice
+#   and this notice are preserved.  This file is offered as-is, without any
+#   warranty.
+
+#serial 6
+
+AC_DEFUN([AX_CHECK_COMPILE_FLAG],
+[AC_PREREQ(2.64)dnl for _AC_LANG_PREFIX and AS_VAR_IF
+AS_VAR_PUSHDEF([CACHEVAR],[ax_cv_check_[]_AC_LANG_ABBREV[]flags_$4_$1])dnl
+AC_CACHE_CHECK([whether _AC_LANG compiler accepts $1], CACHEVAR, [
+  ax_check_save_flags=$[]_AC_LANG_PREFIX[]FLAGS
+  _AC_LANG_PREFIX[]FLAGS="$[]_AC_LANG_PREFIX[]FLAGS $4 $1"
+  AC_COMPILE_IFELSE([m4_default([$5],[AC_LANG_PROGRAM()])],
+    [AS_VAR_SET(CACHEVAR,[yes])],
+    [AS_VAR_SET(CACHEVAR,[no])])
+  _AC_LANG_PREFIX[]FLAGS=$ax_check_save_flags])
+AS_VAR_IF(CACHEVAR,yes,
+  [m4_default([$2], :)],
+  [m4_default([$3], :)])
+AS_VAR_POPDEF([CACHEVAR])dnl
+])dnl AX_CHECK_COMPILE_FLAGS