rust-lang/rust-clippy

from_iter_instead_of_collect / needless_collect interaction questionable

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#6,533 opened on Jan 1, 2021

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 (2 comments) (0 reactions) (0 assignees)Rust (1,391 forks)batch import
C-enhancementI-false-negativeL-nurserygood first issue

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Description

for _i in Vec::from_iter([1, 2, 3].iter()) {}

clippy will suggest to use .collect() instead of from_iter() here but blindly replacing will not work because .collect() will need some kind of type hint.

Them again

for _i in [1, 2, 3].iter().collect::<Vec<&i32>>() {}

does not trigger clippy::needless_collect (although it should!; neither does the first example) because we can iterate over

for _i in [1, 2, 3].iter() {}

directly.

Contributor guide

Research direction
Investigate the `from iter instead of collect` and `needless collect` lints in Clippy's source code, likely in files like `clippy lints/src/from iter instead of collect.rs` and `clippy lints/src/needless collect.rs`. Determine how they interact and why the suggestion to use `collect()` fails without type hints. Consider adjusting the lint to either suggest a proper type hint or suppress the suggestion when it would cause an error. Also check if `needless collect` should trigger for the `from iter` case.
Tech stack
rust
Domain
tooling
Issue type
Bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Fresh
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Mostly clear
Prerequisites
Basic understanding of Rust lintsFamiliarity with Clippy's lint structure
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
40