The real meaning of CS0161 isn't really "does every possible code path return a value", but rather: "is there a code path that somehow reaches the end of the method and does not return a value". The compiler is cleverly detecting that while (true) without a break is a loop that can't be exited to continue after the while, so: there is no way of reaching the end of the method. So: it isn't doing anything wrong from the compiler's perspective.
It is still very wrong, of course.
Note: if you add:
static bool AlwaysTrue() => true;
and change to while (AlwaysTrue()), it will now give you a CS0161 error, because this detection of a non-exited loop is specific to constant expressions that it can trivially evaluate as true.
It has nothing to do with running a Task in the background. It would do the same if you had an int or string as a return type.
Similarly, it will give you a CS0162 warning (unreachable code detected) if you do:
while (false)
{
Console.WriteLine("Hi");
}
Thanks Marc for your explanation. The only thing I still have hard time to understand is why the following code compiles: private Task StartDataCollection() { while(true) { } } but not without the while(true) loop.
@RaminToussi again: show me a semantically valid code path where it reaches the end of the method without returning a value - there isn't one, because the compiler knows that a
while(true)loop without abreaknever exits to go beyond thewhile