Isn't a philosophy/CS double major kind of like a math/CS double major? In that it expands your knowledge in the same domain, rather than a completely new one would (like, for example, studying German literature or biology would).
I remember helping my sister with her philosophy home work, and being surprised by the amount of elementary logic and set theory being taught.
That depends in large part on the philosophy department. More analytic [1] departments will teach lots of courses that could just as well be cross-listed as theoretical computer science courses.
But some departments are less analytic (e.g. departments heavy on [2] and [3] aren't too difficult to find in the US). In those departments, the mode of thinking is very different from what you'll experience in a CS course.
And in both cases, taking a lot of humanity courses will teach you how to write well. Which is definitely a skill that a lot of CS majors lack.
(Also, a course of study in analytic philosophy can definitely help round out a CS major that's too light on the theory courses.)
Other than a class on logic, all of my other courses involved enormous amount of written argumentation, e.g., reasoning, ancient philosophy, modern philosophy, Asian philosophy, philosophy of mind, philosophy of science, philosophy of film, metaphysics, etc. I would say that only logic had a direction connection to computer science, although as a computer scientist, I would choose to write essays about the Turing test, philosophy of AI, etc. This was 15+ years ago, but I assume things are still the same in many philosophy departments.
I remember helping my sister with her philosophy home work, and being surprised by the amount of elementary logic and set theory being taught.