thread 'rustc' panicked at 'print_if saw if with weird alternative'

[vamolessa]

I got this error on my code even though it did not have any print in it.
Also, it seems to only happen on lib crates.
Just a cargo check is enough to reproduce it.

rust playground: https://play.rust-lang.org/?version=stable&mode=debug&edition=2018&gist=b2f77ee4a258355673f15d73bd345007

Code

use std::path::Path;
struct A {
    pub func: fn(check: bool, a: &Path, b: Option<&Path>),
}
const MY_A: A = A {
    func: |check, a, b| {
        if check {
            let _ = ();
        } else if let Some(parent) = b.and_then(|p| p.parent()) {
            let _ = ();
        }
    },
};

Meta

The bug also happens on beta and nightly versions of the compiler.

rustc --version --verbose:

rustc 1.51.0 (2fd73fabe 2021-03-23)
binary: rustc
commit-hash: 2fd73fabe469357a12c2c974c140f67e7cdd76d0
commit-date: 2021-03-23
host: x86_64-pc-windows-msvc
release: 1.51.0
LLVM version: 11.0.1

Error output

thread 'rustc' panicked at 'print_if saw if with weird alternative', compiler\rustc_hir_pretty\src\lib.rs:1106:25
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 1.51.0 (2fd73fabe 2021-03-23) running on x86_64-pc-windows-msvc

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

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

query stack during panic:
end of query stack

Backtrace

N/A

[vamolessa]

Oh, I think it's worth noting that if the code is refatored as:

use std::path::Path;
struct A {
    pub func: fn(check: bool, a: &Path, b: Option<&Path>),
}
const MY_A: A = A {
    func: |check, a, b| {
        if check {
            let _ = ();
        } else {
            // put the if let on another line
            if let Some(parent) = b.and_then(|p| p.parent()) {
                let _ = ();
            }
        }
    },
};

The bug ceases to happen.

[apiraino]

I think duplicated of #82329 ?

[jyn514]

@apiraino this one doesn't need nightly to trigger

[vamolessa]

The code in #82329 works for me

[jyn514]

@vamolessa right, because it's a different problem and only triggers with -Zunpretty=hir,typed.

[syvb]

The issue seems to be that the else if let gets desugared to a match, which is currently unexpected in an else branch.

@rustbot claim