Range patterns that cover the full range, and unit struct/variant patterns do not "read the value"

See https://github.com/rust-lang/miri/issues/4237 for a previous similar issue.

I tried this code:

fn main() {
    let c: char;
    let char::MIN..=char::MAX = c;
}

I expected a compile error. Instead, the code compiled without errors.

My mental model is that matching against char::MIN..=char::MAX should at least "verify" that the bit pattern is a valid char, not to mention uninitialized bytes. Therefore, the pattern should "read" from c, and produce a compile error.

This also has an effect on opsem. For example, Miri doesn't report UB in the following code:

enum Foo {
    A(char), // valid values: 0..=0x10FFFF
    B,       // valid value:      0x110000
}
fn main() {
    unsafe {
        let x: u32 = 0x110001;
        let invalid: *const Foo = (&raw const x).cast();
        match *invalid {
            Foo::B => {}
            Foo::A(ref c @ char::MIN..=char::MAX) => {}
        }
    }
}

See https://github.com/rust-lang/rust/issues/91095 for more context about how niches work in opsem.

Meta

Reproducible on the playground with version 1.96.0-nightly (2026-03-03 d9563937fa3b030c5845)

Start by reproducing the two Rust examples from the issue on the stated nightly version, then read the related discussions in rust-lang/miri#4237 and rust-lang/rust#91095. Determine the intended pattern-matching and opsem behavior for full-range and unit struct/variant patterns; done means the invalid or uninitialized values are handled consistently and regression coverage exists.