map_entry warning does not consider possible intervening code

[jmafc]

Version: clippy 0.0.212 (d4092ac 2020-05-11)
I get the following warning:

172 | /         if !seen.contains_key(&url) {
173 | |             v.push(Href {url: url.clone(), title: row.get("title")});
174 | |             seen.insert(url, 1);
175 | |         }
    | |_________^ consider using `seen.entry(url)`

The warning doesn't take into account that the contains_key() / insert() sequence has some code that is necessary in between (it could also apply if the push() was placed after the insert(). For context, this is inside a loop iterating over rows and the Hashmap seen is used to prevent inserting duplicates into the vector v. AFAICT (I've tried several variations of using Entry methods), using the suggested or_insert() does not provide a solution.

[ghost]

What about...

if let Entry::Vacant(entry) = seen.entry(url) {
    v.push(Href {url: url.clone(), title: row.get("title")});
    entry.insert(1);
}

Now you're only looking up the key once so it should be faster. Aside from looking nicer.

[jmafc]

Yes, that works (except for having to use url.clone() in the first rather than the second one). I'm still wondering, though, whether the warning is always valid, irrespective of other code in the block following the contains_key().

[ghost]

There are cases. entry() mutably borrows the Hashmap so the suggestion is invalid if you're using the hashmap for something else in the block. See #4674.