Clippy recommending odd and broken (macro?) syntax in fix

[sigaloid]

Running cargo +nightly clippy on my fork.

fn pattern_to_vec(pattern: &str) -> Pattern {
        pattern
            .trim_matches('/')
            .split('/')
            .flat_map(|s| {
                if let Some(idx) = s.find('.') {
                     vec![s[..idx].to_string(), s[idx..].to_string()]
                 } else {
                     vec![s.to_string()]
                 }
            })
            .collect::<Vec<_>>()
    }

The fix that is given to me for this if let Some:

warning: use Option::map_or_else instead of an if let/else
   --> src/router.rs:85:17
    |
85  | /                 if let Some(idx) = s.find('.') {
86  | |                     vec![s[..idx].to_string(), s[idx..].to_string()]
87  | |                 } else {
88  | |                     vec![s.to_string()]
89  | |                 }
    | |_________________^ help: try: `s.find('.').map_or_else(|| <[_]>::into_vec(box [$($x),+]), |idx| <[_]>::into_vec(box [$($x),+]))`
    |

This fix doesn't compile at all, the syntax is just borked.

The original function:

The errors given when implementing the suggestion:

The right fix:

You can test this out on the codebase:

git clone https://github.com/sigaloid/vial
cd vial/
git checkout dfc9b61cba9436baa87931bae389e114d342437e
cargo +nightly clippy

(it's the third warning from the bottom)

If I had to guess it would be something to do with the fact that it's an if statement inside of map_or_else, or maybe the vec macro?

Meta

Rust version (rustc -Vv):

rustc 1.56.1 (59eed8a2a 2021-11-01)
binary: rustc
commit-hash: 59eed8a2aac0230a8b53e89d4e99d55912ba6b35
commit-date: 2021-11-01
host: x86_64-unknown-linux-gnu
release: 1.56.1
LLVM version: 13.0.0

@rustbot label +I-suggestion-causes-error

clippy: clippy::option_if_let_else

note: the lint level is defined here
   --> src/lib.rs:214:5
    |
214 |     clippy::nursery,
    |     ^^^^^^^^^^^^^^^
    = note: `#[warn(clippy::option_if_let_else)]` implied by `#[warn(clippy::nursery)]`
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#option_if_let_else

[matthiaskrgr]

I think the problem is that the suggestion contains the expanded vec![] macro.