`clippy` was not able to apply suggested fixes

[AngheloAlf]

Summary

Hey! I'm a Rust newbie and I'm working on porting an existing Python library to Rust. I tried running clippy on the project, it was able to improve some code but it seems to have choked when I tried to run it after some changes were applied. The tool told me to open an issue on https://github.com/rust-lang/rust/issues, but that page has a link specifically for clippy bugs, so here I am.

Reproducer

The specific repository and commit that should be able to reproduce the issue: Decompollaborate/mapfile_parser@5a3f70c

Link to pastebin containing full output of clippy: https://pastebin.com/WG20z4Ay

My understanding is the following code is the culprit (permalink)

        let mut aux_dict = HashMap::new();
       // ...

            let mut path: PathBuf;
            // ...

            if !aux_dict.contains_key(&path) {
                aux_dict.insert(path, vec![file]);
            } else {
                aux_dict.get_mut(&path).unwrap().push(file);
            }

clippy tried to convert it to some very verbose Entry::Vacant, but it failed in the process

I was told either one of the following would be an ideal way of writing the insertion:

match aux_dict.entry(path) {
    Entry::Vacant(e) => {
        e.insert(vec![file]);
    }
    Entry::Occupied(e) => {
        e.into_mut().push(file);
    }
}

or

aux_dict.entry(path).or_default().push(file);

Version

rustc 1.70.0 (90c541806 2023-05-31)
binary: rustc
commit-hash: 90c541806f23a127002de5b4038be731ba1458ca
commit-date: 2023-05-31
host: x86_64-unknown-linux-gnu
release: 1.70.0
LLVM version: 16.0.2

Additional Labels

No response

[ada4a]

The good news is, this code no longer causes a faulty suggestion. The bad news is, now the doesn't emit a suggestion at all, just a warning -- which is a shame, but I'm afraid creating an automated suggestion here would require quite deep analysis of the code.

I think this situation could be improved a bit by directing the user to the Entry API, at least by including a link to it.