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Add a lint to warn about &(dyn … + Send) #110937

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m-ou-se opened this issue Apr 28, 2023 · 4 comments
Open

Add a lint to warn about &(dyn … + Send) #110937

m-ou-se opened this issue Apr 28, 2023 · 4 comments
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@john-h-k
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A-diagnostics Area: Messages for errors, warnings, and lints C-feature-request Category: A feature request, i.e: not implemented / a PR. E-help-wanted Call for participation: Help is requested to fix this issue. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue.

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@m-ou-se
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m-ou-se commented Apr 28, 2023 •
edited by rustbot
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Adding + Send to a &dyn is a useless restriction. E.g. &(dyn Any + Send) implicitly converts to &dyn Any, but not the other way around, even though it'd be sound to just transmute it in both directions, since the Send isn't of any use for (shared) references.

It'd be nice if we suggest removing the + Send for &(dyn … + Send).

See #110799
@m-ou-se m-ou-se added A-diagnostics Area: Messages for errors, warnings, and lints T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. E-help-wanted Call for participation: Help is requested to fix this issue. C-feature-request Category: A feature request, i.e: not implemented / a PR. labels Apr 28, 2023
@john-h-k
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Would this make the most sense as a rustc lint or a clippy lint?

@m-ou-se
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m-ou-se commented Apr 28, 2023

I think as a rustc lint.

cc @rust-lang/types who probably have an opinion on this.

@john-h-k
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@rustbot claim

@john-h-k john-h-k mentioned this issue Apr 28, 2023
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@steffahn
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Using the dyn-clone crate, &dyn Trait + Send can be useful, right?

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A-diagnostics Area: Messages for errors, warnings, and lints C-feature-request Category: A feature request, i.e: not implemented / a PR. E-help-wanted Call for participation: Help is requested to fix this issue. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue.
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Create unnecessary_send_constraint lint for &(dyn ... + Send) john-h-k/rust
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@m-ou-se @steffahn @john-h-k