[maybe] false positive on clippy::needless-collect #8753
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C-bug
Category: Clippy is not doing the correct thing
I-false-positive
Issue: The lint was triggered on code it shouldn't have
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magnusja
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bors
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Aug 21, 2022
feat(fix): Do not lint if the target code is inside a loop close #8753 we consider the following code. ```rust fn main() { let vec = vec![1]; let w: Vec<usize> = vec.iter().map(|i| i * i).collect(); // <- once. for i in 0..2 { let _ = w.contains(&i); } } ``` and the clippy will issue the following warning. ```rust warning: avoid using `collect()` when not needed --> src/main.rs:3:51 | 3 | let w: Vec<usize> = vec.iter().map(|i| i * i).collect(); | ^^^^^^^ ... 6 | let _ = w.contains(&i); | -------------- the iterator could be used here instead | = note: `#[warn(clippy::needless_collect)]` on by default = 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 | 3 ~ 4 | 5 | for i in 0..2 { 6 ~ let _ = vec.iter().map(|i| i * i).any(|x| x == i); ``` Rewrite the code as indicated. ```rust fn main() { let vec = vec![1]; for i in 0..2 { let _ = vec.iter().map(|i| i * i).any(|x| x == i); // <- execute `map` every loop. } } ``` this code is valid in the compiler, but, it is different from the code before the rewrite. So, we should not lint, If `collect` is outside of a loop. Thank you in advance. --- changelog: Do not lint if the target code is inside a loop in `needless_collect`
bors
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Aug 21, 2022
feat(fix): Do not lint if the target code is inside a loop close #8753 we consider the following code. ```rust fn main() { let vec = vec![1]; let w: Vec<usize> = vec.iter().map(|i| i * i).collect(); // <- once. for i in 0..2 { let _ = w.contains(&i); } } ``` and the clippy will issue the following warning. ```rust warning: avoid using `collect()` when not needed --> src/main.rs:3:51 | 3 | let w: Vec<usize> = vec.iter().map(|i| i * i).collect(); | ^^^^^^^ ... 6 | let _ = w.contains(&i); | -------------- the iterator could be used here instead | = note: `#[warn(clippy::needless_collect)]` on by default = 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 | 3 ~ 4 | 5 | for i in 0..2 { 6 ~ let _ = vec.iter().map(|i| i * i).any(|x| x == i); ``` Rewrite the code as indicated. ```rust fn main() { let vec = vec![1]; for i in 0..2 { let _ = vec.iter().map(|i| i * i).any(|x| x == i); // <- execute `map` every loop. } } ``` this code is valid in the compiler, but, it is different from the code before the rewrite. So, we should not lint, If `collect` is outside of a loop. Thank you in advance. --- changelog: Do not lint if the target code is inside a loop in `needless_collect`
bors
added a commit
that referenced
this issue
Aug 21, 2022
feat(fix): Do not lint if the target code is inside a loop close #8753 we consider the following code. ```rust fn main() { let vec = vec![1]; let w: Vec<usize> = vec.iter().map(|i| i * i).collect(); // <- once. for i in 0..2 { let _ = w.contains(&i); } } ``` and the clippy will issue the following warning. ```rust warning: avoid using `collect()` when not needed --> src/main.rs:3:51 | 3 | let w: Vec<usize> = vec.iter().map(|i| i * i).collect(); | ^^^^^^^ ... 6 | let _ = w.contains(&i); | -------------- the iterator could be used here instead | = note: `#[warn(clippy::needless_collect)]` on by default = 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 | 3 ~ 4 | 5 | for i in 0..2 { 6 ~ let _ = vec.iter().map(|i| i * i).any(|x| x == i); ``` Rewrite the code as indicated. ```rust fn main() { let vec = vec![1]; for i in 0..2 { let _ = vec.iter().map(|i| i * i).any(|x| x == i); // <- execute `map` every loop. } } ``` this code is valid in the compiler, but, it is different from the code before the rewrite. So, we should not lint, If `collect` is outside of a loop. Thank you in advance. --- changelog: Do not lint if the target code is inside a loop in `needless_collect`
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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:
I saw this happen:
I expected to see this happen:
nothing, should be ok
Version
Additional Labels
No response
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