[clang-tools-extra] [clang-tidy] Avoid processing declarations in system headers (PR #128150)

[Gábor Horváth via cfe-commits]

Xazax-hun wrote:

> But at this time point, there are no other sub project use it, which means it is not a common part.

Using this logic we would almost never move anything to reusable libraries. In LLVM, we tend to introduce reusable componantes/functionality a lot. As far as I remember, when ASTMatchers were first introduced, they only had one upstream user, Clang Tidy. Still, it was added as a reusable component. The cross translation unit library in clang has exactly one user upstream, the Clang Static Analyzer. We still introduced it as a reusable component. 

If we do not make it accessible to other use cases, we do not get more users or more testing. 

https://github.com/llvm/llvm-project/pull/128150