[gtfierro]

Going beyond this being a minor optimization that isn't going to matter for most people, my guess is that they probably don't reorder structs because it may not be what the programmer intended. When you start introducing mechanisms for altering how the compiler sees a certain piece of code (like a struct definition), then you also need to give the programmer a way of expressing which thing they want the compiler to do, like with __attribute__ in C. Adding that feature in a straightforward way would probably involve introducing more syntax, which Go wants to avoid.

[masklinn]

At the same time, getting either source-layout guarantees or a way to explicitly specify layout is necessary for some task types, to avoid false sharing for instance. Go currently does neither.