[Goal]: mgca variant with no syntax questions

[BoxyUwU]

Foo<direct!(<T as Trait>::ASSOC)> and #[typeconst] const ASSOC: usize as well as no const blocks required to get an anon const. Requiring explicit const blocks is untenable as it breaks half the ecosystem and is wildly backwards incompatible :)

[BoxyUwU]

@rustbot assign @khyperia

cc https://github.com/rust-lang/rust/compare/main...BoxyUwU:gcas_no_explicit_anon_const?expand=1 my initial draft of looking into this to see what it'd take. we need to handle array lengths somehow as right now they get a DefId made by the def collector and that's "wrong".

we can either just accept these "fake" defids existing and hack around them, or we can try and make the def collector not make them (which is harder). it may be worth revisiting hacking up the def collector even though past attempts failed miserably 😅