Clippy fix makes breaking change on warning: usage of `contains_key` followed by `insert` on a `HashMap`

[dchen5022]

Summary

Clippy attempts to fix the warning: usage of contains_key followed by insert on a HashMap
and creates a borrow after move.

Original:

let name = format!("{}/{}", sensor_driver.namespace, sensor_driver.function);
if sensor_drivers.contains_key(&name) {
    res.error(format!("Duplicate sensor driver {} in drivers file.", name));
} else {
    sensor_drivers.insert(name, sensor_driver);
}

Clippy Fixed:

let name = format!("{}/{}", sensor_driver.namespace, sensor_driver.function);
if let std::collections::hash_map::Entry::Vacant(e) = sensor_drivers.entry(name) {
  e.insert(sensor_driver);
} else {
  res.error(format!("Duplicate sensor driver {} in drivers file.", name));
}

The Clippy generated code results in name being moved by HashMap::Entry before being borrowed by format!.

Version

rustc 1.81.0 (eeb90cda1 2024-09-04)
binary: rustc
commit-hash: eeb90cda1969383f56a2637cbd3037bdf598841c
commit-date: 2024-09-04
host: aarch64-apple-darwin
release: 1.81.0
LLVM version: 18.1.7

Additional Labels

No response

[zjp-CN]

Seems to have been fixed since #14314 .

Well, no.

After that PR, clippy still emits warnings for non-Copy key if the key will be in use, which brings error[E0382]: borrow of moved value.

[ada4a]

Since #15546, this no longer creates an invalid suggestion at all; the diagnostic now looks like this:

warning: usage of `contains_key` followed by `insert` on a `HashMap`
  --> src/main.rs:11:5
   |
11 | /     if map.contains_key(&key) {
12 | |         error(format!("Duplicate sensor driver {} in drivers file.", key));
13 | |     } else {
14 | |         map.insert(key, val);
15 | |     }
   | |_____^
   |
   = help: consider using the `Entry` API: https://doc.rust-lang.org/std/collections/struct.HashMap.html#entry-api

[ada4a]

Oh and it turns out that you can indeed use the Entry API here:

let name = format!("{}/{}", sensor_driver.namespace, sensor_driver.function);
match sensor_drivers.entry(name) {
    Entry::Occupied(o) => {
        res.error(format!(
            "Duplicate sensor driver {} in drivers file.",
            o.key()
        ));
    }
    Entry::Vacant(v) => {
        v.insert(sensor_driver);
    }
}

Maybe I'll be able to create an automated suggestion for that...