configure: enable Lua if found and continue without if not

configure.ac

@@ -174,29 +174,43 @@ m4_ifdef([PKG_CHECK_VAR], [],
 # Lua module and scripts
 AC_ARG_ENABLE([lua],
 	[AC_HELP_STRING([--enable-lua], [enable lua binding])],
-	[enable_lua=yes], [enable_lua=no])
+	[], [enable_lua=check])
 
 AC_ARG_WITH([lua-pc],
 	[AS_HELP_STRING(
 		[--with-lua-pc=PKG],
 		[Specify pkg-config package name for lua]
-	)],
+	)], [], [with_lua_pc=no])
+
+if test "x$enable_lua" = "xyes" -a "x$with_lua_pc" != "xno"; then
+	# exit with error if not found
+	PKG_CHECK_MODULES([LUA], [$with_lua_pc], [LUAPKGCONFIG=$with_lua_pc])
+fi
+
+if test "x$enable_lua" = "xcheck" -a "x$with_lua_pc" != "xno"; then
+	PKG_CHECK_MODULES([LUA], [$with_lua_pc],
 		[LUAPKGCONFIG=$with_lua_pc
-	enable_lua=yes])
+		enable_lua=yes],
+		[enable_lua=no])
+fi
+
+if test "x$enable_lua" != "xno"; then
+	PKG_CHECK_MODULES([LUA], [lua], [LUAPKGCONFIG=lua],
+		[PKG_CHECK_MODULES([LUA], [lua5.2], [LUAPKGCONFIG=lua5.2],
+			[PKG_CHECK_MODULES([LUA], [lua5.1], [LUAPKGCONFIG=lua5.1],
+				[AS_IF([test "x$enable_lua" = "xyes"],
+					[AC_MSG_ERROR([Lua not found. Please use --with-lua-pc=PKG])],
+					[enable_lua=no])]
+			)]
+		)])
+	AS_IF([test "x$LUAPKGCONFIG" != "x"], [enable_lua=yes])
+fi
 
 AM_CONDITIONAL([ENABLE_LUA],
 	[test "x$enable_lua" = "xyes"])
 
 AM_COND_IF([ENABLE_LUA],
-	[AS_IF([test "x$with_lua_pc" = "xyes"],
-		[PKG_CHECK_MODULES([LUA], [lua],[LUAPKGCONFIG=lua],
-			[PKG_CHECK_MODULES([LUA], [lua5.2],[LUAPKGCONFIG=lua5.2],
-				[PKG_CHECK_MODULES([LUA], [lua5.1],
-					[LUAPKGCONFIG=lua5.1])]
-			)]
-		)],
-		[PKG_CHECK_MODULES([LUA], [$with_lua_pc])])
-	AC_MSG_CHECKING([Lua version])
+	[AC_MSG_CHECKING([Lua version])
 	PKG_CHECK_VAR([LUA_VERSION], [$LUAPKGCONFIG], [V],,
 		[PKG_CHECK_VAR([LUA_VERSION], [$LUAPKGCONFIG], [major_version])])
 	AC_MSG_RESULT([$LUA_VERSION])