superbuild/modules/SDL2/acinclude/pkg_config.m4

# PKG_PROG_PKG_CONFIG([MIN-VERSION])
# ----------------------------------
AC_DEFUN([PKG_PROG_PKG_CONFIG],
[m4_pattern_forbid([^_?PKG_[A-Z_]+$])
m4_pattern_allow([^PKG_CONFIG(_PATH)?$])
AC_ARG_VAR([PKG_CONFIG], [path to pkg-config utility])
AC_ARG_VAR([PKG_CONFIG_PATH], [directories to add to pkg-config's search path])
AC_ARG_VAR([PKG_CONFIG_LIBDIR], [path overriding pkg-config's built-in search path])

if test "x$ac_cv_env_PKG_CONFIG_set" != "xset"; then
	AC_PATH_TOOL([PKG_CONFIG], [pkg-config])
fi
if test -n "$PKG_CONFIG"; then
	_pkg_min_version=m4_default([$1], [0.9.0])
	AC_MSG_CHECKING([pkg-config is at least version $_pkg_min_version])
	if $PKG_CONFIG --atleast-pkgconfig-version $_pkg_min_version; then
		AC_MSG_RESULT([yes])
	else
		AC_MSG_RESULT([no])
		PKG_CONFIG=""
	fi
fi[]dnl
])# PKG_PROG_PKG_CONFIG

# PKG_CHECK_EXISTS(MODULES, [ACTION-IF-FOUND], [ACTION-IF-NOT-FOUND])
#
# Check to see whether a particular set of modules exists.  Similar
# to PKG_CHECK_MODULES(), but does not set variables or print errors.
#
# Please remember that m4 expands AC_REQUIRE([PKG_PROG_PKG_CONFIG])
# only at the first occurence in configure.ac, so if the first place
# it's called might be skipped (such as if it is within an "if", you
# have to call PKG_CHECK_EXISTS manually
# --------------------------------------------------------------
AC_DEFUN([PKG_CHECK_EXISTS],
[AC_REQUIRE([PKG_PROG_PKG_CONFIG])dnl
if test -n "$PKG_CONFIG" && \
    AC_RUN_LOG([$PKG_CONFIG --exists --print-errors "$1"]); then
  m4_default([$2], [:])
m4_ifvaln([$3], [else
  $3])dnl
fi])

# _PKG_CONFIG([VARIABLE], [COMMAND], [MODULES])
# ---------------------------------------------
m4_define([_PKG_CONFIG],
[if test -n "$$1"; then
    pkg_cv_[]$1="$$1"
 elif test -n "$PKG_CONFIG"; then
    PKG_CHECK_EXISTS([$3],
                     [pkg_cv_[]$1=`$PKG_CONFIG --[]$2 "$3" 2>/dev/null`],
		     [pkg_failed=yes])
 else
    pkg_failed=untried
fi[]dnl
])# _PKG_CONFIG

# _PKG_SHORT_ERRORS_SUPPORTED
# -----------------------------
AC_DEFUN([_PKG_SHORT_ERRORS_SUPPORTED],
[AC_REQUIRE([PKG_PROG_PKG_CONFIG])
if $PKG_CONFIG --atleast-pkgconfig-version 0.20; then
        _pkg_short_errors_supported=yes
else
        _pkg_short_errors_supported=no
fi[]dnl
])# _PKG_SHORT_ERRORS_SUPPORTED


# PKG_CHECK_MODULES(VARIABLE-PREFIX, MODULES, [ACTION-IF-FOUND],
# [ACTION-IF-NOT-FOUND])
#
#
# Note that if there is a possibility the first call to
# PKG_CHECK_MODULES might not happen, you should be sure to include an
# explicit call to PKG_PROG_PKG_CONFIG in your configure.ac
#
#
# --------------------------------------------------------------
AC_DEFUN([PKG_CHECK_MODULES],
[AC_REQUIRE([PKG_PROG_PKG_CONFIG])dnl
AC_ARG_VAR([$1][_CFLAGS], [C compiler flags for $1, overriding pkg-config])dnl
AC_ARG_VAR([$1][_LIBS], [linker flags for $1, overriding pkg-config])dnl

pkg_failed=no
AC_MSG_CHECKING([for $1])

_PKG_CONFIG([$1][_CFLAGS], [cflags], [$2])
_PKG_CONFIG([$1][_LIBS], [libs], [$2])

m4_define([_PKG_TEXT], [Alternatively, you may set the environment variables $1[]_CFLAGS
and $1[]_LIBS to avoid the need to call pkg-config.
See the pkg-config man page for more details.])

if test $pkg_failed = yes; then
   	AC_MSG_RESULT([no])
        _PKG_SHORT_ERRORS_SUPPORTED
        if test $_pkg_short_errors_supported = yes; then
	        $1[]_PKG_ERRORS=`$PKG_CONFIG --short-errors --print-errors "$2" 2>&1`
        else 
	        $1[]_PKG_ERRORS=`$PKG_CONFIG --print-errors "$2" 2>&1`
        fi
	# Put the nasty error message in config.log where it belongs
	echo "$$1[]_PKG_ERRORS" >&AS_MESSAGE_LOG_FD

	m4_default([$4], [AC_MSG_ERROR(
[Package requirements ($2) were not met:

$$1_PKG_ERRORS

Consider adjusting the PKG_CONFIG_PATH environment variable if you
installed software in a non-standard prefix.

_PKG_TEXT])dnl
        ])
elif test $pkg_failed = untried; then
     	AC_MSG_RESULT([no])
	m4_default([$4], [AC_MSG_FAILURE(
[The pkg-config script could not be found or is too old.  Make sure it
is in your PATH or set the PKG_CONFIG environment variable to the full
path to pkg-config.

_PKG_TEXT

To get pkg-config, see <http://pkg-config.freedesktop.org/>.])dnl
        ])
else
	$1[]_CFLAGS=$pkg_cv_[]$1[]_CFLAGS
	$1[]_LIBS=$pkg_cv_[]$1[]_LIBS
        AC_MSG_RESULT([yes])
	$3
fi[]dnl
])# PKG_CHECK_MODULES