ICE when initializing static array of struct containing function pointer using const function

[vamolessa]

Code

I think it's worth noting that the error goes away if we either:

• we remove the f field from Thing (or just remove the for<'a> from the function signature and replace the PhantomData<&'a ()> with just PhantomData<()>);
• we substitute both calls to bad_hash in second Thing's h field initialization with a literal (e.g. 0 for example);

pub const fn bad_hash(_bytes: &[u8]) -> u64 {
    0
}

struct Thing {
    pub h: u64,
    pub f: for<'a> fn(std::marker::PhantomData<&'a ()>),
}

static THINGS: &[Thing] = &[
    Thing {
        h: bad_hash(b"abc"),
        f: |_| (),
    },
    Thing {
        h: bad_hash(b"abc"),
        f: |_| (),
    },
];

pub fn main() {
    for t in THINGS {
        dbg!(t.h);
    }
}

Meta

The bug also happens on beta and nightly.

rustc --version --verbose:

rustc 1.53.0 (53cb7b09b 2021-06-17)
binary: rustc
commit-hash: 53cb7b09b00cbea8754ffb78e7e3cb521cb8af4b
commit-date: 2021-06-17
host: x86_64-pc-windows-msvc
release: 1.53.0
LLVM version: 12.0.1

Error output

thread 'rustc' panicked at 'called `Option::unwrap()` on a `None` value', compiler\rustc_mir\src\borrow_check\region_infer\mod.rs:2136:35
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

error: internal compiler error: unexpected panic

note: the compiler unexpectedly panicked. this is a bug.

note: we would appreciate a bug report: https://github.com/rust-lang/rust/issues/new?labels=C-bug%2C+I-ICE%2C+T-compiler&template=ice.md

note: rustc 1.53.0 (53cb7b09b 2021-06-17) running on x86_64-pc-windows-msvc

note: compiler flags: -C embed-bitcode=no -C debuginfo=2 -C incremental --crate-type bin

note: some of the compiler flags provided by cargo are hidden

query stack during panic:
#0 [mir_borrowck] borrow-checking `THINGS`
#1 [analysis] running analysis passes on this crate
end of query stack
error: could not compile `ice`

Backtrace

thread 'rustc' panicked at 'called `Option::unwrap()` on a `None` value', compiler\rustc_mir\src\borrow_check\region_infer\mod.rs:2136:35
stack backtrace:
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

error: internal compiler error: unexpected panic

note: the compiler unexpectedly panicked. this is a bug.

note: we would appreciate a bug report: https://github.com/rust-lang/rust/issues/new?labels=C-bug%2C+I-ICE%2C+T-compiler&template=ice.md

note: rustc 1.53.0 (53cb7b09b 2021-06-17) running on x86_64-pc-windows-msvc

note: compiler flags: -C embed-bitcode=no -C debuginfo=2 -C incremental --crate-type bin

note: some of the compiler flags provided by cargo are hidden

query stack during panic:
#0 [mir_borrowck] borrow-checking `THINGS`
#1 [analysis] running analysis passes on this crate
end of query stack
error: could not compile `ice`

To learn more, run the command again with --verbose.

[hellow554]

Looks like a dup of #84957

[vamolessa]

Oh, you're right!
Sorry about the dup, I found it hard to describe this issue so I didn't know what to search for.

Should we just close this then?
Is there value in pasting this code on that thread?

[hellow554]

No worries! I happens to me a lot as well ;)

I found it hard to describe this issue so I didn't know what to search for.

I try to search for the line that causes the ICE, in your case I would search for compiler\rustc_mir\src\borrow_check\region_infer\mod.rs

Should we just close this then?

Yes please :)

Is there value in pasting this code on that thread?

Totally!
You could add a post saying "I used this code and have the same ICE", so it would (hopefully) be added to the test suite so this ICE will never be triggered again.

Hope that helps. Thanks for your report!

[vamolessa]

Alright, thanks!