E0277: the trait bound `*const _: From<&Foo>` is not satisfied

I tried this code:

[package]
name = "foo"
version = "0.1.0"
edition = "2024"

[dependencies]
security-framework-sys = { version = "=2.17.0", default-features = false }

#[allow(unused)]
use security_framework_sys;

#[repr(u8)]
pub enum Foo {
    A,
    B,
    C,
}

impl Foo {
    pub fn discriminant(self) -> u8 {
        // SAFETY: Because `Foo` is marked `repr(u8)`, its layout is a `repr(C)`
        // `union` between `repr(C)` structs, each of which has the `u8`
        // discriminant as its first field, so we can read the discriminant
        // without offsetting the pointer.
        unsafe { *<*const _>::from(&self).cast::<u8>() }
    }
}

I expected to see this happen: The code compiles.

Instead, this happened: The fails to compile with the following error:

error[E0277]: the trait bound `*const _: From<&Foo>` is not satisfied
  --> src/lib.rs:17:20
   |
17 |         unsafe { *<*const _>::from(&self).cast::<u8>() }
   |                    ^^^^^^^^ the trait `From<&Foo>` is not implemented for `*const _`

error[E0282]: type annotations needed
  --> src/lib.rs:17:19
   |
17 |         unsafe { *<*const _>::from(&self).cast::<u8>() }
   |                   ^^^^^^^^^^^^^^^^^^^^^^^ ---- cannot call a method on a raw pointer with an unknown pointee type
   |                   |
   |                   cannot infer type

Some errors have detailed explanations: E0277, E0282.
For more information about an error, try `rustc --explain E0277`.
error: could not compile `aaa` (lib) due to 2 previous errors

On nightly I only get the first error:

error[E0277]: the trait bound `*const _: From<&Foo>` is not satisfied
  --> src/lib.rs:17:20
   |
17 |         unsafe { *<*const _>::from(&self).cast::<u8>() }
   |                    ^^^^^^^^ the trait `From<&Foo>` is not implemented for `*const _`

For more information about this error, try `rustc --explain E0277`.
error: could not compile `aaa` (lib) due to 1 previous error

Meta

rustc --version --verbose:

rustc 1.93.1 (01f6ddf75 2026-02-11)
binary: rustc
commit-hash: 01f6ddf7588f42ae2d7eb0a2f21d44e8e96674cf
commit-date: 2026-02-11
host: aarch64-apple-darwin
release: 1.93.1
LLVM version: 21.1.8

rustc +nightly --version --verbose

rustc 1.96.0-nightly (80381278a 2026-03-01)
binary: rustc
commit-hash: 80381278a08582356c13b0f52af92d27c567c230
commit-date: 2026-03-01
host: aarch64-apple-darwin
release: 1.96.0-nightly
LLVM version: 22.1.0

I can also reproduce it on Linux:
rustc --version --verbose:

rustc 1.93.1 (01f6ddf75 2026-02-11)
binary: rustc
commit-hash: 01f6ddf7588f42ae2d7eb0a2f21d44e8e96674cf
commit-date: 2026-02-11
host: x86_64-unknown-linux-gnu
release: 1.93.1
LLVM version: 21.1.8

rustc +nightly --version --verbose

rustc 1.96.0-nightly (80381278a 2026-03-01)
binary: rustc
commit-hash: 80381278a08582356c13b0f52af92d27c567c230
commit-date: 2026-03-01
host: x86_64-unknown-linux-gnu
release: 1.96.0-nightly
LLVM version: 22.1.0

I originally discovered this in a project that uses reqwest. The relevant code have nothing to do with reqwest and the compile error only happened on macOS, not on Linux.

Start by compiling the provided src/lib.rs reproducer with the stable and nightly rustc versions listed, on macOS and Linux, focusing on <*const _>::from(&self).cast::<u8>(). Trace the compiler's handling of raw-pointer type inference and From<&Foo>, then add regression coverage showing the expected compilation behavior.