[clang] [clang][Diagnostics] Highlight code snippets (PR #66514)

[Vlad Serebrennikov via cfe-commits]

Endilll wrote:

> > As mentioned above, `-fno-color-diagnostics` is the flag you can deploy internally this very moment.
> 
> Disabling color diagnostics would make the job of other software engineers harder, right? This hammer is a bit too big for the problem at hand, right?

I thought we are still talking about internal work being blocked on this, which is much more severe issue.


https://github.com/llvm/llvm-project/pull/66514