Wrong coloring on "consider removing this method call"

[est31]

Consider this code:

use std::collections::{HashMap, HashSet};
fn foo() -> Vec<(bool, HashSet<u8>)> {
	let mut hm = HashMap::<bool, Vec<HashSet<u8>>>::new();
	hm.into_iter()
		.map(|(is_true, ts)| {
			ts.into_iter()
				.map(|t| (is_true, t))
				.flatten()
		})
		.flatten()
		.collect()
}

It gives:

error[E0277]: `(bool, HashSet<u8>)` is not an iterator
    --> a.rs:8:6
     |
8    |                 .flatten()
     |                  ^^^^^^^ `(bool, HashSet<u8>)` is not an iterator
     |
     = help: the trait `Iterator` is not implemented for `(bool, HashSet<u8>)`
     = note: required for `(bool, HashSet<u8>)` to implement `IntoIterator`
note: required by a bound in `flatten`
    --> src/rust/library/core/src/iter/traits/iterator.rs:1517:21
     |
1514 |     fn flatten(self) -> Flatten<Self>
     |        ------- required by a bound in this associated function
...
1517 |         Self::Item: IntoIterator,
     |                     ^^^^^^^^^^^^ required by this bound in `Iterator::flatten`
help: consider removing this method call, as the receiver has type `std::vec::IntoIter<HashSet<u8>>` and `std::vec::IntoIter<HashSet<u8>>: Iterator` trivially holds
     |
6    -             ts.into_iter()
7    -                 .map(|t| (is_true, t))
6    +             ts.into_iter()
     |

error[E0277]: `(bool, HashSet<u8>)` is not an iterator
   --> a.rs:4:2
    |
4   | /     hm.into_iter()
5   | |         .map(|(is_true, ts)| {
6   | |             ts.into_iter()
7   | |                 .map(|t| (is_true, t))
8   | |                 .flatten()
9   | |         })
    | |__________^ `(bool, HashSet<u8>)` is not an iterator
    |
    = help: the trait `Iterator` is not implemented for `(bool, HashSet<u8>)`
    = note: required for `(bool, HashSet<u8>)` to implement `IntoIterator`
note: required by a bound in `Flatten`
   --> src/rust/library/core/src/iter/adapters/flatten.rs:254:38
    |
254 | pub struct Flatten<I: Iterator<Item: IntoIterator>> {
    |                                      ^^^^^^^^^^^^ required by this bound in `Flatten`

error[E0599]: the method `collect` exists for struct `Flatten<Map<IntoIter<bool, Vec<HashSet<u8>>>, ...>>`, but its trait bounds were not satisfied
   --> a.rs:11:4
    |
4   | /     hm.into_iter()
5   | |         .map(|(is_true, ts)| {
6   | |             ts.into_iter()
7   | |                 .map(|t| (is_true, t))
...   |
10  | |         .flatten()
11  | |         .collect()
    | |         -^^^^^^^ method cannot be called due to unsatisfied trait bounds
    | |_________|
    |
    |
   ::: src/rust/library/core/src/iter/adapters/flatten.rs:254:1
    |
254 |   pub struct Flatten<I: Iterator<Item: IntoIterator>> {
    |   --------------------------------------------------- doesn't satisfy `<_ as IntoIterator>::IntoIter = _`, `<_ as IntoIterator>::Item = _`, `_: IntoIterator` or `_: Iterator`
    |
    = note: the full type name has been written to 'a.long-type-10511036807638515192.txt'
    = note: consider using `--verbose` to print the full type name to the console
    = note: the following trait bounds were not satisfied:
            `<Flatten<Map<std::vec::IntoIter<HashSet<u8>>, {closure@a.rs:7:10: 7:13}>> as IntoIterator>::IntoIter = _`
            which is required by `Flatten<Map<std::collections::hash_map::IntoIter<bool, Vec<HashSet<u8>>>, {closure@a.rs:5:8: 5:23}>>: Iterator`
            `<Flatten<Map<std::vec::IntoIter<HashSet<u8>>, {closure@a.rs:7:10: 7:13}>> as IntoIterator>::Item = _`
            which is required by `Flatten<Map<std::collections::hash_map::IntoIter<bool, Vec<HashSet<u8>>>, {closure@a.rs:5:8: 5:23}>>: Iterator`
            `Flatten<Map<std::vec::IntoIter<HashSet<u8>>, {closure@a.rs:7:10: 7:13}>>: IntoIterator`
            which is required by `Flatten<Map<std::collections::hash_map::IntoIter<bool, Vec<HashSet<u8>>>, {closure@a.rs:5:8: 5:23}>>: Iterator`
            `Flatten<Map<std::collections::hash_map::IntoIter<bool, Vec<HashSet<u8>>>, {closure@a.rs:5:8: 5:23}>>: Iterator`
            which is required by `&mut Flatten<Map<std::collections::hash_map::IntoIter<bool, Vec<HashSet<u8>>>, {closure@a.rs:5:8: 5:23}>>: Iterator`

My bug report is about the coloring in this particular suggestion:

removing the red parts will obviously make the situation worse and cause parsing errors.

Even if you remove the entire map function call, it won't fix all the errors, what is needed is the removal of flatten. I want to make this particular issue about the wrong coloring of that red part: there is some mistake about it.

Appears on latest nightly rustc 1.85.0-nightly (a4cb3c831 2024-12-17) as well as beta rustc 1.84.0-beta.4 (202008a1b 2024-12-07).

[ionicmc-rs]

why didnt you just give the part that had the incorrect color... but anyways thats kinda weird

[jieyouxu]

I suspect it's the suggestion using some replacement span which is not quite accurate to the syntax.

[estebank]

The issue is that the highlighting logic doesn't account for "the removed snippet is multiline". We need to look for newlines in the part when the "after" code is an empty string. I'm looking at a way to fix it at the moment.

Thank you for the report! I've noticed some highlights being off, but never managed to capture a good repro when encountering them. This is very useful!