[clang] [clang] Add clang::debug_info_type attribute for bitfields (PR #69104)

[Erich Keane via cfe-commits]

erichkeane wrote:

> > One thing I REALLY hate about our pattern of using bitfields for enums, is that it becomes pretty trivial to add an entry to an enum and forget to increase the size of the bitfield. I think such a attribute could cause a diagnostic of `bitfield says it holds an ENUM type, but can't store all the values`, which would be INCREDIBLY valuable (not that I'm pushing that this patch IMPLEMENT that, but more that I'm saying such a name COULD do that, and probably should as well).
> > So in conclusion, I don't mind the name, but also prefer something more general.
> 
> Couldn't we add a warning for that in general? Seems like a pretty useful one to me.

Not without SOME sort of psychic-level analysis from Sema.  Without some level of mapping of "I mean for this to hold the values of this Enum", we don't have the information to do so.  We cannot take advantage of assignments (though a similar warning DOES exist in the 'range' checking) since it might be intended that the field does some level of 'conversion' between enums.

https://github.com/llvm/llvm-project/pull/69104