Wrapper<T> where bounds recursion error

[zeroflaw]

I tried this code:

pub struct Enc<T>(T);

pub trait Encode {}
impl<A> Encode for Enc<Vec<A>> where Enc<A>: Encode {}

pub fn write() where Enc<()>: Encode {}

I expected this to compile.

Instead, this happened:

error[E0275]: overflow evaluating the requirement `_: Sized`
help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`playground`)
note: required for `Enc<Vec<_>>` to implement `Encode`

A more verbose example:
If T is explicitly typed, the code will compile. feel free to comment out the line in the playground version to see a working example.

#[test]
fn call_write() {
    write(&1_i8); //ERROR (recursion: overflow evaluating the requirement?)
    write::<i8>(&1_i8); // OK without the above line
}

pub struct Enc<T: ?Sized>(pub *const T);

pub fn write<T>(_: &T) where Enc<T>: Encode {}

pub trait Encode {}
impl Encode for Enc<i8> {}
impl<A> Encode for Enc<Vec<A>> where Enc<A>: Encode {}

https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=d4352d96adc9ea2b8290c346a38a948e

Meta

This also occurs on stable

rustc --version --verbose:

rustc 1.86.0-nightly (f027438f8 2025-02-03)
binary: rustc
commit-hash: f027438f8bc6b747528dca8b8de13043544d7238
commit-date: 2025-02-03
host: x86_64-unknown-linux-gnu
release: 1.86.0-nightly
LLVM version: 19.1.7

[theemathas]

Duplicate of #113496 (comment)