Actually, it's not. The compiler using the comments for non-commenting purposes makes me puke. It's a dirty workaround and degradation of the language.
If you want a new compiler feature, add a new statement.
If you want a new compiler feature, add a new statement.
Otherwise these magic comments will grow into their own unaudited meta language with no formal spec, just a few usage examples.
This and struct tags (another stringy metalanguage) are the bits I’m not keen on in Go.
The go 1 guarantee only says that existing go programs will continue to compile correctly on new releases. It doesn't say that new programs will compile correctly on old releases.