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dnl Use lots of warning flags with with gcc and compatible compilers

dnl Note: if you change the following variable, the cache is automatically
dnl skipped and all flags rechecked.  So there's no need to do anything
dnl else.  If for any reason you need to force a recheck, just change
dnl MAYBE_WARN in an ignorable way (like adding whitespace)

MAYBE_WARN="-Wall -Wextra \
-Wsign-compare -Werror-implicit-function-declaration \
-Wpointer-arith -Wwrite-strings -Wstrict-prototypes \
-Wmissing-prototypes -Wmissing-declarations -Wnested-externs \
-Wpacked -Wswitch-enum -Wmissing-format-attribute \
-Wstrict-aliasing=2 -Winit-self -Wunsafe-loop-optimizations \
-Wdeclaration-after-statement -Wold-style-definition \
-Wno-missing-field-initializers -Wno-unused-parameter \
-Wno-attributes -Wno-long-long -Winline"

dnl We also abuse the warning-flag facility to enable other compiler
dnl options.  Namely, the following:
MAYBE_WARN="$MAYBE_WARN -fno-strict-aliasing"

# invalidate cached value if MAYBE_WARN has changed
if test "x$cairo_cv_warn_maybe" != "x$MAYBE_WARN"; then
	unset cairo_cv_warn_cflags
fi
AC_CACHE_CHECK([for supported warning flags], cairo_cv_warn_cflags, [
	echo
	WARN_CFLAGS=""

	# Some warning options are not supported by all versions of
	# gcc, so test all desired options against the current
	# compiler.
	#
	# Note that there are some order dependencies
	# here. Specifically, an option that disables a warning will
	# have no net effect if a later option then enables that
	# warnings, (perhaps implicitly). So we put some grouped
	# options (-Wall and -Wextra) up front and the -Wno options
	# last.

	for W in $MAYBE_WARN; do
		CAIRO_CC_TRY_FLAG([$W], [WARN_CFLAGS="$WARN_CFLAGS $W"])
	done

	cairo_cv_warn_cflags=$WARN_CFLAGS
	cairo_cv_warn_maybe=$MAYBE_WARN

	AC_MSG_CHECKING([which warning flags were supported])
])
WARN_CFLAGS="$cairo_cv_warn_cflags"
CAIRO_CFLAGS="$CAIRO_CFLAGS $WARN_CFLAGS"

# We only wish to enable attribute(warn_unused_result) if we can prevent
# gcc from generating thousands of warnings about the misapplication of the
# attribute to void functions and variables.
AC_CACHE_CHECK([how to enable unused result warnings], cairo_cv_warn_unused_result, [
	cairo_cv_warn_unused_result=""
	if echo $WARN_CFLAGS | grep -e '-Wno-attributes' >/dev/null; then
	    AC_TRY_COMPILE([__attribute__((__warn_unused_result__))
		int f (int i) { return i; }], [],
		[cairo_cv_warn_unused_result="__attribute__((__warn_unused_result__))"])
	fi
])
AC_DEFINE_UNQUOTED([WARN_UNUSED_RESULT], [$cairo_cv_warn_unused_result],
	  [Define to the value your compiler uses to support the warn-unused-result attribute])