+# =============================================================================
+# https://www.gnu.org/software/autoconf-archive/ax_compiler_flags_cflags.html
+# =============================================================================
+#
+# SYNOPSIS
+#
+# AX_COMPILER_FLAGS_CFLAGS([VARIABLE], [IS-RELEASE], [EXTRA-BASE-FLAGS], [EXTRA-YES-FLAGS])
+#
+# DESCRIPTION
+#
+# Add warning flags for the C compiler to VARIABLE, which defaults to
+# WARN_CFLAGS. VARIABLE is AC_SUBST-ed by this macro, but must be
+# manually added to the CFLAGS variable for each target in the code base.
+#
+# This macro depends on the environment set up by AX_COMPILER_FLAGS.
+# Specifically, it uses the value of $ax_enable_compile_warnings to decide
+# which flags to enable.
+#
+# LICENSE
+#
+# Copyright (c) 2014, 2015 Philip Withnall <philip@tecnocode.co.uk>
+# Copyright (c) 2017, 2018 Reini Urban <rurban@cpan.org>
+#
+# 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 17
+
+AC_DEFUN([AX_COMPILER_FLAGS_CFLAGS],[
+ AC_REQUIRE([AC_PROG_SED])
+ AX_REQUIRE_DEFINED([AX_APPEND_COMPILE_FLAGS])
+ AX_REQUIRE_DEFINED([AX_APPEND_FLAG])
+ AX_REQUIRE_DEFINED([AX_CHECK_COMPILE_FLAG])
+
+ # Variable names
+ m4_define([ax_warn_cflags_variable],
+ [m4_normalize(ifelse([$1],,[WARN_CFLAGS],[$1]))])
+
+ AC_LANG_PUSH([C])
+
+ AC_COMPILE_IFELSE([AC_LANG_PROGRAM([
+ [#ifndef __cplusplus
+ #error "no C++"
+ #endif]])],
+ [ax_compiler_cxx=yes;],
+ [ax_compiler_cxx=no;])
+
+ # Always pass -Werror=unknown-warning-option to get Clang to fail on bad
+ # flags, otherwise they are always appended to the warn_cflags variable, and
+ # Clang warns on them for every compilation unit.
+ # If this is passed to GCC, it will explode, so the flag must be enabled
+ # conditionally.
+ AX_CHECK_COMPILE_FLAG([-Werror=unknown-warning-option],[
+ ax_compiler_flags_test="-Werror=unknown-warning-option"
+ ],[
+ ax_compiler_flags_test=""
+ ])
+
+ # Check that -Wno-suggest-attribute=format is supported
+ AX_CHECK_COMPILE_FLAG([-Wno-suggest-attribute=format],[
+ ax_compiler_no_suggest_attribute_flags="-Wno-suggest-attribute=format"
+ ],[
+ ax_compiler_no_suggest_attribute_flags=""
+ ])
+
+ # Base flags
+ AX_APPEND_COMPILE_FLAGS([ dnl
+ -fno-strict-aliasing dnl
+ $3 dnl
+ ],ax_warn_cflags_variable,[$ax_compiler_flags_test])
+
+ AS_IF([test "$ax_enable_compile_warnings" != "no"],[
+ if test "$ax_compiler_cxx" = "no" ; then
+ # C-only flags. Warn in C++
+ AX_APPEND_COMPILE_FLAGS([ dnl
+ -Wnested-externs dnl
+ -Wmissing-prototypes dnl
+ -Wstrict-prototypes dnl
+ -Wdeclaration-after-statement dnl
+ -Wimplicit-function-declaration dnl
+ -Wold-style-definition dnl
+ -Wjump-misses-init dnl
+ ],ax_warn_cflags_variable,[$ax_compiler_flags_test])
+ fi
+
+ # "yes" flags
+ AX_APPEND_COMPILE_FLAGS([ dnl
+ -Wall dnl
+ -Wextra dnl
+ -Wundef dnl
+ -Wwrite-strings dnl
+ -Wpointer-arith dnl
+ -Wmissing-declarations dnl
+ -Wredundant-decls dnl
+ -Wno-unused-parameter dnl
+ -Wno-missing-field-initializers dnl
+ -Wformat=2 dnl
+ -Wcast-align dnl
+ -Wformat-nonliteral dnl
+ -Wformat-security dnl
+ -Wsign-compare dnl
+ -Wstrict-aliasing dnl
+ -Wshadow dnl
+ -Winline dnl
+ -Wpacked dnl
+ -Wmissing-format-attribute dnl
+ -Wmissing-noreturn dnl
+ -Winit-self dnl
+ -Wredundant-decls dnl
+ -Wmissing-include-dirs dnl
+ -Wunused-but-set-variable dnl
+ -Warray-bounds dnl
+ -Wreturn-type dnl
+ -Wswitch-enum dnl
+ -Wswitch-default dnl
+ -Wduplicated-cond dnl
+ -Wduplicated-branches dnl
+ -Wlogical-op dnl
+ -Wrestrict dnl
+ -Wnull-dereference dnl
+ -Wdouble-promotion dnl
+ $4 dnl
+ $5 dnl
+ $6 dnl
+ $7 dnl
+ ],ax_warn_cflags_variable,[$ax_compiler_flags_test])
+ ])
+ AS_IF([test "$ax_enable_compile_warnings" = "error"],[
+ # "error" flags; -Werror has to be appended unconditionally because
+ # it's not possible to test for
+ #
+ # suggest-attribute=format is disabled because it gives too many false
+ # positives
+ AX_APPEND_FLAG([-Werror],ax_warn_cflags_variable)
+
+ AX_APPEND_COMPILE_FLAGS([ dnl
+ [$ax_compiler_no_suggest_attribute_flags] dnl
+ ],ax_warn_cflags_variable,[$ax_compiler_flags_test])
+ ])
+
+ # In the flags below, when disabling specific flags, always add *both*
+ # -Wno-foo and -Wno-error=foo. This fixes the situation where (for example)
+ # we enable -Werror, disable a flag, and a build bot passes CFLAGS=-Wall,
+ # which effectively turns that flag back on again as an error.
+ for flag in $ax_warn_cflags_variable; do
+ AS_CASE([$flag],
+ [-Wno-*=*],[],
+ [-Wno-*],[
+ AX_APPEND_COMPILE_FLAGS([-Wno-error=$(AS_ECHO([$flag]) | $SED 's/^-Wno-//')],
+ ax_warn_cflags_variable,
+ [$ax_compiler_flags_test])
+ ])
+ done
+
+ AC_LANG_POP([C])
+
+ # Substitute the variables
+ AC_SUBST(ax_warn_cflags_variable)
+])dnl AX_COMPILER_FLAGS
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