C bitfields guarantees

[cc]

On Friday, 5 July 2024 at 05:37:50 UTC, Richard (Rikki) Andrew 
Cattermole wrote:
> Today many people have spent some time to try and understand 
> Walter's belief that C is "good enough" for bit fields in terms 
> of guarantees.

Can I define my D struct using bitfields, and then correctly 
unpack them in a GLSL shader using bitfieldExtract() with the 
predicted offsets and sizes?  If the answer is no, then that 
bitfield implementation belongs in a garbage can.

Currently the answer to this question is "yes" for std.bitmanip 
and "no" for "native" D bitfields.