[PATCH] D55466: Change `tuple_size` from a `class` to a `struct` (see PR#39871)

[Eric Fiselier via Phabricator]

EricWF accepted this revision.
EricWF added a comment.
This revision is now accepted and ready to land.

LGTM.

Consider adding a `*.fail.cpp` test that declares a specialization as a `class` and checks for

  // expected-error {{tuple_size' defined as a class template here but previously declared as a struct template}}


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  https://reviews.llvm.org/D55466/new/

https://reviews.llvm.org/D55466