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Implement derives for Reborrow and CoerceShared#156338

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P8L1:derive-reborrow-coerce-shared
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Implement derives for Reborrow and CoerceShared#156338
P8L1 wants to merge 1 commit into
rust-lang:mainfrom
P8L1:derive-reborrow-coerce-shared

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@P8L1 P8L1 commented May 8, 2026 •
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This adds built-in derive support for the experimental Reborrow and CoerceShared marker traits behind #![feature(reborrow)].

The derives generate the same marker impls users would write manually, while preserving the existing coherence and structural validation path for the experimental reborrow traits.

Please note this impl:

  • Preserves generics, lifetimes, const params, and where clauses in generated impls.
  • Preserves multiple lifetime parameters in generated impls instead of duplicating the current experimental one-lifetime limitation in the derive layer.
  • Requires an explicit CoerceShared target type through the derive helper attribute.
  • Adds UI coverage for valid derives, feature gating, malformed helper attributes, unsupported item kinds, validation failures, and multiple-lifetime derive behavior.
  • Makes the derive layer future-proof for multiple lifetimes: it preserves all lifetime parameters and generates the same impl shape as a manual impl.

@rustbot label F-reborrow
Tracking: #145612

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rustbot commented May 8, 2026

rust-analyzer is developed in its own repository. If possible, consider making this change to rust-lang/rust-analyzer instead.

cc @rust-lang/rust-analyzer

@rustbot rustbot added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label May 8, 2026
@rustbot rustbot added T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. T-libs Relevant to the library team, which will review and decide on the PR/issue. T-rust-analyzer Relevant to the rust-analyzer team, which will review and decide on the PR/issue. labels May 8, 2026
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rustbot commented May 8, 2026

r? @tiif

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@P8L1 P8L1 force-pushed the derive-reborrow-coerce-shared branch 2 times, most recently from c515771 to 1a83d37 Compare May 8, 2026 19:01
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@P8L1 P8L1 force-pushed the derive-reborrow-coerce-shared branch from 1a83d37 to 8e2ead2 Compare May 8, 2026 20:06
@P8L1 P8L1 mentioned this pull request May 9, 2026
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ChayimFriedman2
ChayimFriedman2 requested changes May 9, 2026
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Please separate the rust-analyzer changes to a new PR in the rust-analyzer repo, there is no reason for them to be here.

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@rustbot rustbot removed the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label May 9, 2026
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rustbot commented May 9, 2026

Reminder, once the PR becomes ready for a review, use @rustbot ready.

@rustbot rustbot added the S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. label May 9, 2026
@P8L1 P8L1 force-pushed the derive-reborrow-coerce-shared branch from 8e2ead2 to 0d49f18 Compare May 9, 2026 20:18
@P8L1 P8L1 mentioned this pull request May 9, 2026
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P8L1 commented May 9, 2026

@rustbot ready

@rustbot rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels May 9, 2026
aapoalas
aapoalas reviewed May 10, 2026
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Comment thread compiler/rustc_builtin_macros/src/deriving/reborrow.rs
}

#[derive(Diagnostic)]
#[diag("`derive(CoerceShared)` requires exactly one `#[coerce_shared(Target)]` attribute", code = E0802)]
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@aapoalas aapoalas May 10, 2026 •
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suggestion: I would've gone with derive(CoerceShared(Target)).

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aapoalas
aapoalas approved these changes May 10, 2026
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Thank you so much for this work. I'm really thankful for the help; I expect this would've taken me quite a bit of time to figure out! <3

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tiif commented May 11, 2026

I don't have enough context to review this, so I will leave this to the compiler champion.

r? @oli-obk

@rustbot rustbot assigned oli-obk and unassigned tiif May 11, 2026
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P8L1 commented May 14, 2026

Hi @oli-obk, no rush, but I wanted to check that this PR is still on your radar.

I know about the usual two-week review window; I’m just making sure it did not get missed after the latest updates. Thanks!

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P8L1 commented May 22, 2026 •
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Oli seems to be very busy ATM so thus:

r? @dingxiangfei2009

Cc. @aapoalas

@rustbot rustbot assigned dingxiangfei2009 and unassigned oli-obk May 22, 2026
@rustbot rustbot added the F-reborrow `#![feature(reborrow)]`; see #145612 label May 22, 2026
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@aapoalas aapoalas aapoalas approved these changes

@ChayimFriedman2 ChayimFriedman2 ChayimFriedman2 approved these changes

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@dingxiangfei2009 dingxiangfei2009

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