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Check that the types in return position impl Trait in traits are well-formed #101676

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merged 1 commit into from
Sep 12, 2022

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@compiler-errors compiler-errors commented Sep 11, 2022

This effectively duplicates check_associated_type_bounds, but that shouldn't be for long, since we're going to remove it once we refactor RPITITs into regular associated items.

Fixes #101663


We don't check

trait Foo {
  fn bar() -> impl ?Sized;
}

currently, but that's for a different reason, which is that we don't currently check that a trait function's return type is sized (i.e. fn bar() -> [u8] also works in a trait).

@rustbot rustbot added the T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. label Sep 11, 2022
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r? @lcnr

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@rust-highfive rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Sep 11, 2022
&& tcx.def_kind(proj.item_def_id) == DefKind::ImplTraitPlaceholder
&& tcx.impl_trait_in_trait_parent(proj.item_def_id) == fn_def_id.to_def_id()
{
let bounds = wfcx.tcx().explicit_item_bounds(proj.item_def_id);
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do we prove the actual item bounds somewhere else? do we already have a test for

#![feature(return_position_impl_trait_in_trait)]
trait Trait {
    fn foo() -> impl Copy { String::new() }
}

this is currently still broken as the following also has the same error 😁

#![feature(return_position_impl_trait_in_trait)]
trait Trait {
    fn foo() -> impl Copy { 3u8 }
}

idk if that's already known

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That is already known, and fixed by another PR

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(#101679 is that issue)

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lcnr commented Sep 12, 2022

@bors r+ rollup

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bors commented Sep 12, 2022

📌 Commit fd2766e has been approved by lcnr

It is now in the queue for this repository.

@bors bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Sep 12, 2022
bors added a commit to rust-lang-ci/rust that referenced this pull request Sep 12, 2022
Rollup of 9 pull requests

Successful merges:

 - rust-lang#100293 (Add inline-llvm option for disabling/enabling LLVM inlining)
 - rust-lang#100767 (Remove manual <[u8]>::escape_ascii)
 - rust-lang#101668 (Suggest pub instead of public for const type item)
 - rust-lang#101671 (Fix naming format of IEEE 754 standard)
 - rust-lang#101676 (Check that the types in return position `impl Trait` in traits are well-formed)
 - rust-lang#101681 (Deny return-position `impl Trait` in traits for object safety)
 - rust-lang#101693 (Update browser UI test 0 10)
 - rust-lang#101701 (Rustdoc-Json: Add tests for trait impls.)
 - rust-lang#101706 (rustdoc: remove no-op `#search`)

Failed merges:

r? `@ghost`
`@rustbot` modify labels: rollup
@bors bors merged commit 5faf033 into rust-lang:master Sep 12, 2022
@rustbot rustbot added this to the 1.65.0 milestone Sep 12, 2022
@compiler-errors compiler-errors deleted the rpitit-wf branch November 2, 2022 02:58
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RPITIT return is not checked for well-formedness
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