Xcode has special behavior for disallowed languages

[Gaztin]

Xcode seems to have special behavior for reinterpreting a file as either objective-c or objective-c++ (referenced below)

premake-core/modules/xcode/xcode_common.lua

Lines 91 to 102 in 2061b15

	function xcode.getfiletype(node, cfg)
	if node.configs then
	local filecfg = fileconfig.getconfig(node, cfg)
	if filecfg then
	if filecfg.language == "ObjC" then
	return "sourcecode.c.objc"
	elseif filecfg.language == "ObjCpp" then
	return "sourcecode.cpp.objcpp"
	end
	end
	end

..but neither of them are allowed languages for file configs.

filter {"files:Foo.cpp"}
    language "ObjCpp"

Above code will, in fact, throw an error (unless I explicitly call api.addAllowed("language", "ObjCpp") ,in which case it works as intended)