`min_generic_const_args` makes `{u,i}*::{MIN, MAX}` ambiguous

[Lars-Schumann]

Enabling mgca somehow breaks these associated consts.

I tried this code: playground

#![allow(incomplete_features)]
#![feature(generic_const_items, min_generic_const_args)]

const TAKES_U8<const FOO: u8>: () = ();
const _: () = TAKES_U8::<{ u8::MAX }>;

I expected to see this happen: compiles.

Instead, this happened: fails to compile. (but compiles fine without mgca enabled)

error[E0223]: ambiguous associated constant
 --> src/lib.rs:5:28
  |
5 | const _: () = TAKES_U8::<{ u8::MAX }>;
  |                            ^^^^^^^
  |
help: you are looking for the module in `std`, not the primitive type
  |
5 | const _: () = TAKES_U8::<{ std::u8::MAX }>;
  |                            +++++

It also compiles fine if you add the const keyword like this:

const _: () = TAKES_U8::<const { u8::MAX }>;

Meta

tested on playground, 1.98.0-nightly (2026-06-26 ce9954c0cfc4bf26b82a)

[peter-lyons-kehl]

Another example:

#![allow(incomplete_features)]
#![feature(min_generic_const_args)]

pub type UsingUsizeMax = [(); usize::MAX];

with rustc 1.97.0 (2d8144b78 2026-07-07)

Feature tracking issue: min_generic_const_args.

[chenyukang]

@khyperia

seems the original issue was resolved by #158617
however, the underlying direct-representation issue remains: using direct_const_arg!(u8::MAX) or enabling macroless_generic_const_args still produces E0223 because HIR type lowering only probes inherent associated items for ADTs.

https://play.rust-lang.org/?version=nightly&mode=debug&edition=2024&gist=1e454a3a903bc8f77a779caf651c4740

[khyperia]

makes sense! seems this is a feature(inherent_associated_types) issue then, feature(generic_const_args) uses that for inherent consts (tbh it should maybe be called feature(inherent_associated_terms), haha). For example:

#![feature(min_generic_const_args)]

struct S;
impl S {
    type const MAX: usize = 2;
}

type A = [(); core::direct_const_arg!(S::MAX)];

produces

error[E0658]: inherent associated types are unstable
 --> src/main.rs:9:39
  |
9 | type C = [(); core::direct_const_arg!(S::MAX)];
  |                                       ^^^^^^
  |
  = note: see issue #8995 <https://github.com/rust-lang/rust/issues/8995> for more information
  = help: add `#![feature(inherent_associated_types)]` to the crate attributes to enable

it's just that when you do u8::MAX, inherent_associated_types is so borked/unimplemented that we don't even get around to being able to emit a feature gate for it.