[clang] [Clang] raise extension warning for unknown namespaced attributes (PR #120925)

[Aaron Ballman via cfe-commits]

AaronBallman wrote:

> @erichkeane @AaronBallman @cor3ntin, just checking if there are any updates on this, as the `Clang 20` release was landed.

Erich and I discussed this more offline and our thinking is:

* It's useful for `-Wunknown-attributes` to print the attribute namespace
* We think there should be typo correction for `-Wunknown-attributes`, for both the attribute namespace and the attribute name
* We're both struggling to find "warn about unknown attribute namespaces" to be motivating because we don't think there are a lot of unknown attribute namespaces in the wild. Does anyone know of a static analysis tool which supplies custom attributes? Or is this currently limited to just plugin attributes in practice? If plugin attributes, we weakly think it might be worth holding off on a separate warning. If there are static analysis tools with custom attributes, then we think that diagnostic is a bit more motivated.


https://github.com/llvm/llvm-project/pull/120925