acinclude: fix variable expansion issues

acinclude.m4

@@ -57,21 +57,33 @@ check_path () {
 
 ])
 
+dnl expand nested ${foo}/bar
+AC_DEFUN([TUXBOX_EXPAND_VARIABLE],[__$1="$2"
+	for __CNT in false false false false true; do dnl max 5 levels of indirection
+
+		$1=`eval echo "$__$1"`
+		echo ${$1} | grep -q '\$' || break # 'grep -q' is POSIX, exit if no $ in variable
+		__$1="${$1}"
+	done
+	$__CNT && AC_MSG_ERROR([can't expand variable $1=$2]) dnl bail out if we did not expand
+])
+
 AC_DEFUN([TUXBOX_APPS_DIRECTORY_ONE],[
 AC_ARG_WITH($1,[  $6$7 [[PREFIX$4$5]]],[
 	_$2=$withval
 	if test "$TARGET" = "cdk"; then
-		$2=`eval echo "${targetprefix}$withval"`
+		$2=`eval echo "${targetprefix}$withval"` # no indirection possible IMNSHO
 	else
 		$2=$withval
 	fi
 	TARGET_$2=${$2}
 ],[
-	$2="\${$3}$5"
+	# RFC 1925: "you can always add another level of indirection..."
+	TUXBOX_EXPAND_VARIABLE($2,"${$3}$5")
 	if test "$TARGET" = "cdk"; then
-		_$2=`eval echo "${target$3}$5"`
+		TUXBOX_EXPAND_VARIABLE(_$2,"${target$3}$5")
 	else
-		_$2=`eval echo "${$3}$5"`
+		_$2=${$2}
 	fi
 	TARGET_$2=$_$2
 ])