Support syntax for one-line trait reuse #150130

aerooneqq · 2025-12-18T15:12:58Z

This PR adds support for reusing the whole trait with a one-line reuse syntax and is part of the delegation feature #118212:

trait T {
  fn foo(&self);
}

struct S;
impl T for S { ... }

struct Wrapper(S);
reuse impl T for Wrapper { self.0 }

The core idea is that we already have support for glob reuse, so in this scenario we want to transform one-line reuse into a trait impl block with a glob reuse in the following way:

//Before
reuse impl T for Wrapper { self.0 }

//After
impl T for Wrapper {
  reuse T::* { self.0 }
}

It seems like this task can be solved during parsing stage, when we encountered a one-line trait reuse, we can expand into this impl block right away, and the code which was already written to expand glob delegations will take care about the rest. We will copy trait path into glob reuse path.

The implementation of the transformation reuses already existing methods for impl parsing, however, we do not parse inner impl items, instead we parse "inner items" as delegation body. Thus, we do not have to deal with generics, consts, unsafe and other impl related features.

Other syntax possibility is trying to shorten one-line reuse by replacing impl keyword with reuse keyword:

reuse T for Wrapper { self.0 }

In this case implementation may become more complicated, and the syntax more confusing, as keywords such as const or unsafe will precede reuse, and there are also generics:

unsafe reuse<T1, T2> T for Wrapper { self.0 }

In the first (currently implemented) version reuse is placed in the beginning of the item, and it is clear that we will reuse trait implementation, while in the second, shorter version, the reuse keyword may be lost in generics and keywords that may precede impl.

r? @petrochenkov

tests/ui/delegation/impl-reuse-pass.rs

compiler/rustc_parse/src/errors.rs

compiler/rustc_parse/src/parser/item.rs

aerooneqq · 2025-12-22T08:53:39Z

@rustbot ready

petrochenkov · 2025-12-22T20:44:03Z

r=me with the test added #150130 (comment) and commits squashed.
@rustbot author

rustbot · 2025-12-22T20:44:07Z

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

compiler/rustc_parse/src/parser/item.rs

aerooneqq · 2025-12-23T07:35:28Z

@rustbot ready

petrochenkov · 2025-12-23T09:47:46Z

@bors r+

bors · 2025-12-23T09:47:48Z

📌 Commit 1de1885 has been approved by petrochenkov

It is now in the queue for this repository.

…t-impl, r=petrochenkov Support syntax for one-line trait reuse This PR adds support for reusing the whole trait with a one-line reuse syntax and is part of the delegation feature rust-lang#118212: ```rust trait T { fn foo(&self); } struct S; impl T for S { ... } struct Wrapper(S); reuse impl T for Wrapper { self.0 } ``` The core idea is that we already have support for glob reuse, so in this scenario we want to transform one-line reuse into a trait impl block with a glob reuse in the following way: ```rust //Before reuse impl T for Wrapper { self.0 } //After impl T for Wrapper { reuse T::* { self.0 } } ``` It seems like this task can be solved during parsing stage, when we encountered a one-line trait reuse, we can expand into this impl block right away, and the code which was already written to expand glob delegations will take care about the rest. We will copy trait path into glob reuse path. The implementation of the transformation reuses already existing methods for `impl` parsing, however, we do not parse inner `impl` items, instead we parse "inner items" as delegation body. Thus, we do not have to deal with generics, consts, unsafe and other `impl` related features. Other syntax possibility is trying to shorten one-line reuse by replacing `impl` keyword with `reuse` keyword: ```rust reuse T for Wrapper { self.0 } ``` In this case implementation may become more complicated, and the syntax more confusing, as keywords such as `const` or `unsafe` will precede `reuse`, and there are also generics: ```rust unsafe reuse<T1, T2> T for Wrapper { self.0 } ``` In the first (currently implemented) version reuse is placed in the beginning of the item, and it is clear that we will reuse trait implementation, while in the second, shorter version, the `reuse` keyword may be lost in generics and keywords that may precede `impl`. r? `@petrochenkov`

…uwer Rollup of 3 pull requests Successful merges: - #150130 (Support syntax for one-line trait reuse) - #150282 (move a ui test to coretests unit test) - #150303 (`target_features::Stability`: tweak docs of `requires_nightly()`) r? `@ghost` `@rustbot` modify labels: rollup

…uwer Rollup of 6 pull requests Successful merges: - #150130 (Support syntax for one-line trait reuse) - #150205 (compiletest: Add `LineNumber` newtype to avoid `+1` magic here and there) - #150282 (move a ui test to coretests unit test) - #150295 (Fix compilation error in hermit-abi time.rs) - #150301 (std: remove unsupported pipe module from VEXos pal) - #150303 (`target_features::Stability`: tweak docs of `requires_nightly()`) r? `@ghost` `@rustbot` modify labels: rollup

bors · 2025-12-23T14:22:47Z

⌛ Testing commit 1de1885 with merge 0bd13c3...

Rollup merge of #150130 - aerooneqq:delegation-one-line-trait-impl, r=petrochenkov Support syntax for one-line trait reuse This PR adds support for reusing the whole trait with a one-line reuse syntax and is part of the delegation feature #118212: ```rust trait T { fn foo(&self); } struct S; impl T for S { ... } struct Wrapper(S); reuse impl T for Wrapper { self.0 } ``` The core idea is that we already have support for glob reuse, so in this scenario we want to transform one-line reuse into a trait impl block with a glob reuse in the following way: ```rust //Before reuse impl T for Wrapper { self.0 } //After impl T for Wrapper { reuse T::* { self.0 } } ``` It seems like this task can be solved during parsing stage, when we encountered a one-line trait reuse, we can expand into this impl block right away, and the code which was already written to expand glob delegations will take care about the rest. We will copy trait path into glob reuse path. The implementation of the transformation reuses already existing methods for `impl` parsing, however, we do not parse inner `impl` items, instead we parse "inner items" as delegation body. Thus, we do not have to deal with generics, consts, unsafe and other `impl` related features. Other syntax possibility is trying to shorten one-line reuse by replacing `impl` keyword with `reuse` keyword: ```rust reuse T for Wrapper { self.0 } ``` In this case implementation may become more complicated, and the syntax more confusing, as keywords such as `const` or `unsafe` will precede `reuse`, and there are also generics: ```rust unsafe reuse<T1, T2> T for Wrapper { self.0 } ``` In the first (currently implemented) version reuse is placed in the beginning of the item, and it is clear that we will reuse trait implementation, while in the second, shorter version, the `reuse` keyword may be lost in generics and keywords that may precede `impl`. r? ``@petrochenkov``

rustbot assigned petrochenkov Dec 18, 2025

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Dec 18, 2025

aerooneqq force-pushed the delegation-one-line-trait-impl branch from 43b3a47 to 829d1bf Compare December 19, 2025 12:59

petrochenkov added the F-fn_delegation `#![feature(fn_delegation)]` label Dec 19, 2025

petrochenkov mentioned this pull request Dec 19, 2025

Tracking Issue for function delegation (fn_delegation, RFC 3530) #118212

Open

29 tasks

petrochenkov reviewed Dec 19, 2025

View reviewed changes

petrochenkov added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Dec 19, 2025

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 Dec 22, 2025

This comment has been minimized.

Sign in to view

rustbot added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Dec 22, 2025

fmease reviewed Dec 22, 2025

View reviewed changes

compiler/rustc_parse/src/parser/item.rs Outdated Show resolved Hide resolved

Support syntax for one-line trait reuse

1de1885

aerooneqq force-pushed the delegation-one-line-trait-impl branch from 1116ce4 to 1de1885 Compare December 23, 2025 07:35

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 Dec 23, 2025

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 Dec 23, 2025

JonathanBrouwer mentioned this pull request Dec 23, 2025

Rollup of 3 pull requests #150305

Closed

JonathanBrouwer mentioned this pull request Dec 23, 2025

Rollup of 6 pull requests #150306

Merged

bors merged commit e156286 into rust-lang:main Dec 23, 2025
11 checks passed

rustbot added this to the 1.94.0 milestone Dec 23, 2025

Uh oh!

Support syntax for one-line trait reuse #150130

Support syntax for one-line trait reuse #150130

Conversation

aerooneqq commented Dec 18, 2025 • edited by rustbot Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

aerooneqq commented Dec 22, 2025

Uh oh!

This comment has been minimized.

petrochenkov commented Dec 22, 2025

Uh oh!

rustbot commented Dec 22, 2025

Uh oh!

Uh oh!

aerooneqq commented Dec 23, 2025

Uh oh!

petrochenkov commented Dec 23, 2025

Uh oh!

bors commented Dec 23, 2025

Uh oh!

Uh oh!

bors commented Dec 23, 2025

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

6 participants

aerooneqq commented Dec 18, 2025 •

edited by rustbot

Loading