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Unsized types in required trait methods #134475

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Unsized types in required trait methods#134475
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A-dyn-traitArea: trait objects, vtable layoutA-lintsArea: Lints (warnings about flaws in source code) such as unused_mut.C-feature-requestCategory: A feature request, i.e: not implemented / a PR.T-langRelevant to the language teamT-typesRelevant to the types team, which will review and decide on the PR/issue.needs-rfcThis change is large or controversial enough that it should have an RFC accepted before doing it.

Description

@ionicmc-rs
ionicmc-rs
opened on Dec 18, 2024

so this issue is a follow up for #134422 (closed as not planned) to suggest making a lint instead.

What the issue talked about

Rust does not check for T: Sized in required trait methods

trait Foo {
    fn bar(self: Self, x: str);
}

The above code compiles, even though Self and str are both ?Sized

this makes the trait unimplementable

impl Foo for [u8] {
    fn bar(self: Self, x: str) {}
}

Produces:

The size for values of type `[u8]` cannot be known at compile time
The size for values of type `str` cannot be known at compile time

For more information please see the RFC

Meta

for anyone who cares, here is rustc --version --verbose

rustc 1.85.0-nightly (21fe748be 2024-12-11)
binary: rustc
commit-hash: 21fe748be15271ea5804e0507cd699b675efe038
commit-date: 2024-12-11
host: x86_64-unknown-linux-gnu
release: 1.85.0-nightly
LLVM version: 19.1.5

Here is the RFC

Activity

  1. rustbot
    added
    needs-triageThis issue may need triage. Remove when done. See docs forge.rust-lang.org/release/issue-triaging
    on Dec 18, 2024

  2. ionicmc-rs commented on Dec 18, 2024

    @ionicmc-rs
    ionicmc-rs
    on Dec 18, 2024 · Hidden as outdated
    Author
  3. rustbot
    added
    T-compilerRelevant to the compiler team, which will review and decide on the PR/issue.
    on Dec 18, 2024
  4. fmease
    added
    C-feature-requestCategory: A feature request, i.e: not implemented / a PR.
    A-dyn-traitArea: trait objects, vtable layout
    T-langRelevant to the language team
    A-lintsArea: Lints (warnings about flaws in source code) such as unused_mut.
    and removed
    T-compilerRelevant to the compiler team, which will review and decide on the PR/issue.
    needs-triageThis issue may need triage. Remove when done. See docs forge.rust-lang.org/release/issue-triaging
    on Dec 18, 2024
  5. ionicmc-rs
    changed the title [-]Unsized receiver in traits[/-] [+]Unsized types in required trait methods[/+] on Dec 18, 2024
  6. jieyouxu
    added
    needs-rfcThis change is large or controversial enough that it should have an RFC accepted before doing it.
    on Dec 18, 2024

  7. ionicmc-rs commented on Dec 18, 2024

    @ionicmc-rs
    ionicmc-rs
    on Dec 18, 2024
    ContributorAuthor

    i will make an rfc as the label suggests

  8. ionicmc-rs commented on Dec 18, 2024

    @ionicmc-rs
    ionicmc-rs
    on Dec 18, 2024
    ContributorAuthor

    here is the rfc

  9. ionicmc-rs commented on Dec 18, 2024

    @ionicmc-rs
    ionicmc-rs
    on Dec 18, 2024 · Hidden as off-topic
    Author

  10. rustbot commented on Dec 18, 2024

    @rustbot
    rustbot
    on Dec 18, 2024 · Hidden as off-topic

  11. ionicmc-rs commented on Dec 18, 2024

    @ionicmc-rs
    ionicmc-rs
    on Dec 18, 2024 · Hidden as off-topic
    Author

  12. workingjubilee commented on Dec 18, 2024

    @workingjubilee
    workingjubilee
    on Dec 18, 2024 · Hidden as off-topic
  13. jieyouxu
    added
    T-typesRelevant to the types team, which will review and decide on the PR/issue.
    on Dec 19, 2024

  14. ionicmc-rs commented on Dec 19, 2024

    @ionicmc-rs
    ionicmc-rs
    on Dec 19, 2024 · Hidden as off-topic
    Author

  15. ionicmc-rs commented on Dec 20, 2024

    @ionicmc-rs
    ionicmc-rs
    on Dec 20, 2024
    ContributorAuthor

    The RFC may not be accepted, but this issue is mildly severe, so can someone come up with a solution

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    A-dyn-traitArea: trait objects, vtable layoutA-lintsArea: Lints (warnings about flaws in source code) such as unused_mut.C-feature-requestCategory: A feature request, i.e: not implemented / a PR.T-langRelevant to the language teamT-typesRelevant to the types team, which will review and decide on the PR/issue.needs-rfcThis change is large or controversial enough that it should have an RFC accepted before doing it.

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