Suggest `Entry::or_default` for `Entry::or_insert_with(Default::default)`

[Arnavion]

For code that calls .or_insert_with(Default::default) on a std::collections::btree_map::Entry or std::collections::hash_map::Entry, clippy should suggest std::collections::btree_map::Entry::or_default and std::collections::hash_map::Entry::or_default

[splashofcrimson]

Hey, I'm a new contributor here - is anyone working on this? If not, may I gave it a shot?

[Manishearth]

Go ahead! Let us know if you need help!

[HarrisonMc555]

@splashofcrimson I just wanted to let you know that if you're wondering how to get started, I think that the lint that i just wrote is really similar. You can find the code here. Hopefully you find it helpful :-)

If you don't want to do it anymore, I could probably take a shot at it.

[wookietreiber]

Without knowing clippy internals, is it possible to issue a warning for any or_insert_with(MyStruct::default), i.e. not just for Default::default?

[llogiq]

I think the right way is to resolve the path and see if it is a Default implementation. Otherwise MyStruct could have its own default function without implementing Default (or worse, while implementing Default another way).

[cauebs]

Seems to me no one is working on this, so I'll give it a go today!

[cauebs]

I understand we don't have to suggest unwrap_or_default for {Option | Result}.unwrap_or(Default::default()) because that is already covered by or_fun_call, correct?

[ebroto]

I understand we don't have to suggest unwrap_or_default for {Option | Result}.unwrap_or(Default::default()) because that is already covered by or_fun_call, correct?

Yes. FYI you can test this quickly in the playground, Clippy can be executed there.

This would not be linted though:

Some(42).unwrap_or_else(Default::default);

This could be improved to suggest unwrap_or_default, but may be the subject of another issue.

And about the maps

map.entry("42").or_insert(Default::default());

Is linted, but recommends or_insert_with(Default::default), which is the subject of this issue. I think it's OK if the suggestion of one lint triggers another lint (as long as it's not circular xD).

This lint should probably be implemented in the methods module.