`const fn`: reported test for a simple `match` with a wildcard-only arm

[Centril]

This works; let's consider adding a test for it since it's a bit of a special case. Reported to be working in #49146 (comment) by @jyn514.

// check-pass

#![feature(const_if_match)]

enum E {
    A,
    B,
    C
}

const fn f(e: E) {
    match e {
        _ => {}
    }
}

[jyn514]

@ecstatic-morse do you mind if I add this? My laptop is no longer broken ^^ so I can actually get some work done without disappearing for a week at a time.

I put this in a file called src/test/ui/consts/control-flow/empty-match.rs and ran ./x.py test --stage 1, is that about the right approach?

[Centril]

@jyn514 It is, but I'd recommend using --pass check to make it go faster. Also use --test-args empty-match to just test that file. Also, I'd rename the test to not suggest match x {}... something like single-arm-match-wild.rs.

[jyn514]

I ran ./x.py test src/test/ui/consts --stage 1 about an hour ago and that worked fine (although it took a while ^^). However, since then I updated nightly and I'm now getting compile errors when building stage 1:

cargo:warning=In file included from ../rustllvm/PassWrapper.cpp:6:0:
cargo:warning=../rustllvm/rustllvm.h:1:10: fatal error: llvm-c/BitReader.h: No such file or directory
cargo:warning= #include "llvm-c/BitReader.h"
cargo:warning=          ^~~~~~~~~~~~~~~~~~~~

What am I doing wrong?

Full error: https://pastebin.com/pbnpgmK9

(cross posted from https://rust-lang.zulipchat.com/#narrow/stream/182449-t-compiler.2Fhelp)