问题:

What does this mean in contrast to "unreachable code detected"?

回答1:

Heuristically unreachable means possibly unreachable code. Unreachable code is certainly unreachable.

回答2:

Here's an example of Resharper giving the cryptic "Heuristically unreachable code" warning:

It's an example of:

Resharper being way to smart for itself, because if you remove it the compiler will complain about a lack of a return statement
Use of a word that is not common lexicon

回答3:

Say you're deleting 2 different kinds of objects in a unit test and you want to use a try/catch for both types.

If you delete one, and then check to see if it was successful without properly casting using:

Assert.IsNull(obj1);

The "IsNull" may always be null because you casted obj1 incorrectly, or did something above the greyed out code incorrectly with obj1, the next try/catch will be greyed out.

Try fixing the thing you're trying to Assert.IsNull and once it's not always null or undefined, the greyed out code will be reachable.