False positive for redundant field names when using range?

[avranju]

For the following code:

fn main() {
    let start = 0;
    let fin = 10;
    let vals: Vec<i32> = (start..fin).map(|v| v * v).collect();
    println!("{:?}", vals);
}

Clippy warns:

warning: redundant field names in struct initialization
 --> src/main.rs:4:27
  |
4 |     let vals: Vec<i32> = (start..fin).map(|v| v * v).collect();
  |                           ^^^^^ help: replace it with: `start`
  |
  = note: #[warn(redundant_field_names)] on by default
  = help: for further information visit https://rust-lang-nursery.github.io/rust-clippy/v0.0.204/index.html#redundant_field_names

Is this a legitimate lint?

[brinchj]

Hi!

As far as I can tell, it looks like #2507 tried to address the issue.

But I can still reproduce it in the Rust playground (tools -> clippy):
https://play.rust-lang.org/?gist=8e1d9d87643e9799fce1c60303ea3bab

I wonder which version includes the PR...

[brinchj]

I can reproduce this locally with Clippy 0.0.198.

[ordovicia]

Latest clippy (v0.0.204) does not lint start..end,
but does (start..end).collect::<Vec<i32>>() and (start..end).map(|v| v * v).collect::<Vec<i32>>().

https://play.rust-lang.org/?gist=3cbade6f25fd49565712e71d0a32de78&version=stable&mode=debug

[flip1995]

It seems that (start..end) has no expansion info, while start..end does.

https://github.com/rust-lang-nursery/rust-clippy/blob/400aab92325de2aa65a2c724c3b5f4337bca11c0/clippy_lints/src/utils/mod.rs#L68-L75

A possible (easy) solution would be to just ignore Range-structs, but I'm not sure if this would be the right thing to do... (already discussed here: #2507 (review)).

[ghost]

I think this is a compiler bug.

When lowering expressions in the compiler, it looks like they go to a lot of trouble to set up a span with the correct context and then they replace it if it's enclosed in a parenthesis. See this branch and this branch in lower_expr. 🤔

[ghost]

Fixed by #3007.

[flip1995]

There should be a test for this, before closing this issue.

[ghost]

Unless I'm mistaken...

There are already tests.
https://github.com/rust-lang-nursery/rust-clippy/blob/b109e1033476390f95c728d674909ef90f0ff0ca/tests/ui/redundant_field_names.rs#L42-L51

The errors were fixed by the commit I referenced.
https://github.com/rust-lang-nursery/rust-clippy/pull/3007/files#diff-09e689a73333ff863d80e74c8d58234f

[flip1995]

These tests are for the unparenthesized case. The bug in this issue is that it didn't work with (start..end)

[ghost]

OK, I'll submit the PR after the build issues are sorted out.