bad type inference for `NonZero::{MIN,MAX}`

[ada4a]

I tried this code:

use std::num::NonZero;

fn main() {
    let x: NonZero<u8> = NonZero::MAX;
}

I expected to see this happen: NonZero::MAX is inferred to be NonZero::<u8>::MAX

Instead, this happened: compilation error

Meta

rustc --version --verbose:

cargo 1.88.0 (873a06493 2025-05-10)
release: 1.88.0
commit-hash: 873a0649350c486caf67be772828a4f36bb4734c
commit-date: 2025-05-10
host: x86_64-unknown-linux-gnu
libgit2: 1.9.0 (sys:0.20.0 vendored)
libcurl: 8.12.1-DEV (sys:0.4.80+curl-8.12.1 vendored ssl:OpenSSL/3.4.1)
ssl: OpenSSL 3.4.1 11 Feb 2025
os: NixOS 25.11.0 [64-bit]

(also tested on latest beta and nightly, using Playground)

Backtrace

error[E0034]: multiple applicable items in scope
 --> src/lib.rs:4:35
  |
4 |     let x: NonZero<u8> = NonZero::MAX;
  |                                   ^^^ multiple `MAX` found
  |
  = note: candidate #1 is defined in an impl for the type `NonZero<i128>`
  = note: candidate #2 is defined in an impl for the type `NonZero<i16>`
  = note: candidate #3 is defined in an impl for the type `NonZero<i32>`
  = note: candidate #4 is defined in an impl for the type `NonZero<i64>`
  = note: and 8 others

For more information about this error, try `rustc --explain E0034`.

[ada4a]

@rustbot label A-inference

[compiler-errors]

This is because the MAX consts for all NonZero<T> are distinct consts. The issue is demonstrated by this example:

struct NonZero<T>(T);

impl NonZero<u8> {
    const MAX: Self = NonZero(u8::MAX);
}

impl NonZero<u16> {
    const MAX: Self = NonZero(u16::MAX);
}

fn main() {
    let x: NonZero<u8> = NonZero::MAX;
}

and the fact that we don't use return type to guide method selection.

This is perhaps fixable now that we have a singular NonZero<T>; if we gave a const MAX to ZeroablePrimitive, we could perhaps unify all the different NonZero<T>::MAX'es.

[cuviper]

For unifying, note that NonZero<char> does not have MIN and MAX at all yet, but maybe it should since char does.