[libcxx-commits] [libcxx] [libc++] Disallow specializing `common_reference` (PR #141465)

[Louis Dionne via libcxx-commits]

ldionne wrote:

> > LGTM but can you add a release note since this _may_ break some code?
> 
> We didn't add release note in #118167. If release note is desired, perhaps it's better to also add one to `20.rst`.

Looking quickly through https://github.com/llvm/llvm-project/pull/118167, it seems that we only added `[[no_specializations]]` to templates that were very uncontroversial, i.e. where the likelihood of a user specializing the template was very low. Since `common_type` is intended to be specialized, I have a feeling that `common_reference` might be more commonly specialized too (by mistake). That's why I think this one could use a release note. WDYT?

https://github.com/llvm/llvm-project/pull/141465