[clang-tools-extra] [clang-doc] add nested namespace test case (PR #97681)

[via cfe-commits]

PeterChou1 wrote:

> To clarify my earlier comment, FileCheck is just matching text on the input based on the check lines. So in this cases the LINE directive should just affect what text will be accepted when doin matching. It won’t try to match the lines to the position in the file being checked.
> 
> If you run into problems, post the errors here, as we can probably help diagnose them.

My bad I think I was mistaken in how the @LINE directive worked initially I think i Fixed up the pr so that it works with it now

https://github.com/llvm/llvm-project/pull/97681