Fix suggestions that need parens in from_iter_instead_of_collect lint

[ThibsG]

Fixes broken suggestions that need parens (i.e.: range)

Fixes: #6648

changelog: none

[rust-highfive]

r? @llogiq

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[ThibsG]

Edit WIP: forgot about the turbo fish, the suggestion is still not working (rustc cannot infer the type)

[giraffate]

How about this case? The suggested code seems not to work.

    let mut b = VecDeque::from_iter(0..3);
    // let mut b = `(0..3).collect::<Vec<_>>()` // the suggested code
    b.push_back(4);

[ThibsG]

Yes indeed, turbofish should be customized to match the type implementing from_iter (here VecDeque)

[ThibsG]

Looks better now.
I wanted to shorten the suggestion from (0..3).collect::<std::collections::VecDeque<i32>>() to (0..3).collect::<VecDeque<i32>>() by removing unneeded std::collections but I am not sure this is even possible so I need to dig more into this.

[giraffate]

I can't find any util method. IMHO it might be good to just convert ty to String and use .split("::").last().unwrap() if .contains("::").

[ThibsG]

Yeah I thought about this also, but it sounds a bit too hacky 😄
Ultimately I will consider it if necessary.

[giraffate]

Okay, and yes it's a little hacky. FYI similar codes already exist here

rust-clippy/clippy_lints/src/macro_use.rs

Lines 79 to 88 in e5a1f22

	if !self.collected.contains(&call_site) {
	let name = if name.contains("::") {
	name.split("::").last().unwrap().to_string()
	} else {
	name.to_string()
	};
	self.mac_refs.push(MacroRefData::new(name, callee.def_site, cx));
	self.collected.insert(call_site);
	}

.

[llogiq]

I agree, using items in scope to shorten the paths seems like a worthwile improvement. However, I don't think that should block this PR.

So I'd r+ this unless you want to continue improving it, @ThibsG.

[ThibsG]

I want to give a try to improve this. I should be able to work on this really soon, and I keep you posted 😉

[camsteffen]

Try cx.tcx.trimmed_def_paths(LOCAL_CRATE).get(&def_id)

[llogiq]

Good improvement so far! If you need something, let me know. Otherwise I'd like to see more tests around the type inference problem outlined by @giraffate.

[llogiq]

@ThibsG this appears to fix the turbofish issue. Good tests, too 👍. Is this ready to merge or do you intend to keep improving this PR?

[camsteffen]

Partially addresses #6533.

This is by no means required for this PR, but I want to make a note. It would be nice to have suggestions that use _ and only specify types that the code has already specified:

• Vec::from_iter() -> collect::<Vec<_>>()
• Vec::<u32>::from_iter() -> collect::<Vec<u32>>()

[ThibsG]

I reworked the turbofish extraction to cover cases like the ones suggested by @camsteffen.

[llogiq]

Great! I think we can have further improvements in a followup PR then. Thanks to both of you!

@bors r+

[bors]

📌 Commit b932587 has been approved by llogiq

[bors]

⌛ Testing commit b932587 with merge 3784cdf...

[bors]

☀️ Test successful - checks-action_dev_test, checks-action_remark_test, checks-action_test
Approved by: llogiq
Pushing 3784cdf to master...