Use this code

namespace ns
{
	template<typename T> T func(T) {}
	template<typename T> T func() = delete;
}

It's a regression starting with 0.17.7, due to code pulled in from VS 15.8: https://developercommunity.visualstudio.com/content/problem/305335/incorrect-c-intellisense-error-delete-can-only-app.html .

For now, we'll just suppress the error completely, until we can get a fix for the bogus cases.