Fix dead code warning when inline const is used in pattern

[nbdd0121]

Fixes #78171

[rust-highfive]

r? @petrochenkov

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[petrochenkov]

I'd never guess that const { ... } patterns use PatKind::Lit internally.
@bors r+

[bors]

📌 Commit 17d18e3822d5e5876fbf9d2ddd6d2b4a6783e117 has been approved by petrochenkov

[nbdd0121]

Actually this approach doesn't catch const { foo() }..2 case. Might be better to save in_pat and set it to false when visiting a AnonConst and restore it after visiting.

[nbdd0121]

Added a test case for using inline const in range pattern

[nbdd0121]

I'd never guess that const { ... } patterns use PatKind::Lit internally.

It's surprising to me as well, but I guess that's probably the easiest way to implement it since it'll need to have a P<Expr> anyway.

[petrochenkov]

Might be better to save in_pat and set it to false when visiting a AnonConst and restore it after visiting.

Yeah, it's a better approach, it should also fix cases like

const fn one() -> i32 {
    1
}

struct S<const C: i32>;

fn main() {
    match S::<1> {
        S::<{one()}> => {}
    }
}

Could you actually add this case too?
And merge all the cases into a single test file, no need to run rustc multiple times to test all of this.

@bors r-

[nbdd0121]

Added and merged

[petrochenkov]

Thanks!
@bors r+

[bors]

📌 Commit e62ecdc has been approved by petrochenkov