H::combine implementation details

[widlarizer]

I'd like to understand abseil's hashing infrastructure not to abuse its internal implementation but to partially replicate it. What I'd like to know is if all the "magic" in H::combine is what I can find in MixingHashState::CombineContiguousImpl and MixingHashState::Mix, but I'm only seeing a forward declaration of a HashStateBase::combine(H state, const T& value, const Ts&... values) in HashStateBase. I don't see a definition in HashState or MixingHashState so I can't check that we arrive at CombineContiguousImpl without doing any other intermediate steps. I'm interested in what exactly happens if I were to hash nested records of typically small (word-sized) members. If struct Foo = { int a; int b; }; struct Bar = {char x; Foo y; bool z; };, I would like to confirm, that the computation of hash of a struct Bar that effectively happens is this, just with extra type stuff which is inlined and erased:

h = Seed();
h = Mix(h, x);
h = Mix(h, a);
h = Mix(h, b);
h = Mix(h, z);
return h;