[maybe] false positive on clippy::needless-collect

[magnusja]

Summary

I think clippy has a false positive on clippy::needless-collect

See also this thread https://gitter.im/rust-lang/rust?at=62690723d30b6b44ebbfcd12

Lint Name

clippy::needless-collect

Reproducer

I tried this code:

fn expensive_search() -> Vec<String> {
    vec![]
}

fn expensive_transformation(s: String) -> String {
    s
}

fn main() {
    let things: Vec<String> = expensive_search()
        .into_iter()
        .map(expensive_transformation)
        .collect();

    for i in 0..100 {
        if things.contains(&i.to_string()) {
            println!("foo");
        }
    }
}

I saw this happen:

error: avoid using `collect()` when not needed
  --> bin/main.rs:13:10
   |
13 |         .collect();
   |          ^^^^^^^
...
16 |         if things.contains(&i.to_string()) {
   |            ------------------------------- the iterator could be used here instead
   |
   = note: `-D clippy::needless-collect` implied by `-D warnings`
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#needless_collect
help: check if the original Iterator contains an element instead of collecting then checking
   |
10 ~     
11 | 
12 |     for i in 0..100 {
13 ~         if expensive_search()
14 +         .into_iter()
15 ~         .map(expensive_transformation).any(|x| x == i.to_string()) {
   |

I expected to see this happen:
nothing, should be ok

Version

rustc 1.60.0 (7737e0b5c 2022-04-04)
binary: rustc
commit-hash: 7737e0b5c4103216d6fd8cf941b7ab9bdbaace7c
commit-date: 2022-04-04
host: x86_64-apple-darwin
release: 1.60.0
LLVM version: 14.0.0

Additional Labels

No response

[kyoto7250]

@rustbot claim