rust-lang/rust-clippy

Catch use of PhantomData that requires T: Sized

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#2,308 创建于 2017年12月27日

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T-middlegood first issue

描述

In Serde the traits we implement for PhantomData should have worked for T: ?Sized, but as a bug they required T: Sized -- fixed in https://github.com/serde-rs/serde/commit/4751627f1cd14cacdf216188ccbb9ab0831e2b3f. Could Clippy have caught this? I struggle to think of any use of PhantomData<T> where T is an unconstrained type parameter where you would not want to allow ?Sized. As a starting point, maybe we could catch impls of the form:

impl<..., T, ...> Trait<...> for PhantomData<T> { /* ... */ }

where there are no trait bounds on T. In this case you pretty much always want T: ?Sized right?

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Rust programmingUnderstanding of Sized traitClippy lint development
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研究方向
Review the Serde commit mentioned (4751627f1cd14cacdf216188ccbb9ab0831e2b3f) to understand the fix. Examine existing Clippy lints that check trait implementations on PhantomData, such as those in the clippy lints crate. The new lint should detect impl blocks for PhantomData<T> where T is unconstrained and suggest adding T: ?Sized. Check comments for any prior attempts or maintainer feedback.