delegation: support simplest output `Self` mapping by aerooneqq · Pull Request #158397 · rust-lang/rust

aerooneqq · 2026-06-25T13:18:22Z

This PR supports simplest output Self mapping for callee path if the following conditions are met (see should_wrap_return_value).

Example:

trait Trait {
    fn method(&self) -> Self;
    fn r#static() -> Self;
    fn raw_S(&self) -> S { S }
}

struct S;
impl Trait for S {
    fn method(&self) -> S { S }
    fn r#static() -> S { S }
}

struct W(S);
impl Trait for W {
    #[attr = Inline(Hint)]
    fn method(self: _) -> _ { Self { 0: Trait::method(self.0) } }
    #[attr = Inline(Hint)]
    fn r#static() -> _ { Trait::r#static() }
    //~^ WARN: function cannot return without recursing [unconditional_recursion]
    #[attr = Inline(Hint)]
    fn raw_S(self: _) -> _ { Trait::raw_S(self.0) }
}

impl W {
    #[attr = Inline(Hint)]
    fn method(self: _) -> _ { Self { 0: Trait::method(self.0) } }
    #[attr = Inline(Hint)]
    fn r#static() -> _ { Trait::r#static() }
    #[attr = Inline(Hint)]
    fn raw_S(self: _) -> _ { Trait::raw_S(self.0) }
}

If the above conditions are met, there is no need to propagate generics of a newtype, as unused generics is an error, thus they should be used in a single field and it can be inferred from the return type of callee path.

~~Accessing signatures through queries produced query cycles in one test, so with_no_trimmed_paths was used to prevent it, though it can cause other cycles in other situations maybe.~~

Part of #118212.
r? @petrochenkov

rustbot · 2026-06-29T14:28:57Z

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

aerooneqq · 2026-07-01T06:04:01Z

@rustbot ready

aerooneqq · 2026-07-01T12:12:49Z

@rustbot ready

petrochenkov · 2026-07-01T12:26:38Z

r=me after addressing #158397 (comment) and squashing commits.
@rustbot author
@bors delegate+

rust-bors · 2026-07-01T12:26:41Z

✌️ @aerooneqq, you can now approve this pull request!

If @petrochenkov told you to "r=me" after making some further change, then please make that change and post @bors r=petrochenkov.

View changes since this delegation.

aerooneqq · 2026-07-01T12:39:36Z

@bors r=petrochenkov

rust-bors · 2026-07-01T12:39:39Z

📌 Commit 92c10f9 has been approved by petrochenkov

It is now in the queue for this repository.

@petrochenkov

…ping, r=petrochenkov delegation: support simplest output `Self` mapping This PR supports simplest output `Self` mapping for callee path if the following conditions are met (see `should_wrap_return_value`). Example: ```rust trait Trait { fn method(&self) -> Self; fn r#static() -> Self; fn raw_S(&self) -> S { S } } struct S; impl Trait for S { fn method(&self) -> S { S } fn r#static() -> S { S } } struct W(S); impl Trait for W { #[attr = Inline(Hint)] fn method(self: _) -> _ { Self { 0: Trait::method(self.0) } } #[attr = Inline(Hint)] fn r#static() -> _ { Trait::r#static() } //~^ WARN: function cannot return without recursing [unconditional_recursion] #[attr = Inline(Hint)] fn raw_S(self: _) -> _ { Trait::raw_S(self.0) } } impl W { #[attr = Inline(Hint)] fn method(self: _) -> _ { Self { 0: Trait::method(self.0) } } #[attr = Inline(Hint)] fn r#static() -> _ { Trait::r#static() } #[attr = Inline(Hint)] fn raw_S(self: _) -> _ { Trait::raw_S(self.0) } } ``` ~If the above conditions are met, there is no need to propagate generics of a newtype, as unused generics is an error, thus they should be used in a single field and it can be inferred from the return type of callee path.~ ~Accessing signatures through queries produced query cycles in one test, so `with_no_trimmed_paths` was used to prevent it, though it can cause other cycles in other situations maybe.~ Part of rust-lang#118212. r? @petrochenkov

…uwer Rollup of 8 pull requests Successful merges: - #150075 (Implement clamp_to) - #158169 (Fix debuginfo compression in bootstrap) - #158397 (delegation: support simplest output `Self` mapping) - #158613 (Fix getrandom fallback test on platforms with `panic=abort`) - #158620 (Remove skip_norm_w/i/p().def_id with a helper) - #158633 (Remove unnecessary `Clone` derives on resolver types) - #158634 (Add missing `needs_drop` check to `DroplessArena`.) - #158647 (Document `strip_circumfix` behavior on overlapping prefix and suffix.)

@petrochenkov

…ping, r=petrochenkov delegation: support simplest output `Self` mapping This PR supports simplest output `Self` mapping for callee path if the following conditions are met (see `should_wrap_return_value`). Example: ```rust trait Trait { fn method(&self) -> Self; fn r#static() -> Self; fn raw_S(&self) -> S { S } } struct S; impl Trait for S { fn method(&self) -> S { S } fn r#static() -> S { S } } struct W(S); impl Trait for W { #[attr = Inline(Hint)] fn method(self: _) -> _ { Self { 0: Trait::method(self.0) } } #[attr = Inline(Hint)] fn r#static() -> _ { Trait::r#static() } //~^ WARN: function cannot return without recursing [unconditional_recursion] #[attr = Inline(Hint)] fn raw_S(self: _) -> _ { Trait::raw_S(self.0) } } impl W { #[attr = Inline(Hint)] fn method(self: _) -> _ { Self { 0: Trait::method(self.0) } } #[attr = Inline(Hint)] fn r#static() -> _ { Trait::r#static() } #[attr = Inline(Hint)] fn raw_S(self: _) -> _ { Trait::raw_S(self.0) } } ``` ~If the above conditions are met, there is no need to propagate generics of a newtype, as unused generics is an error, thus they should be used in a single field and it can be inferred from the return type of callee path.~ ~Accessing signatures through queries produced query cycles in one test, so `with_no_trimmed_paths` was used to prevent it, though it can cause other cycles in other situations maybe.~ Part of rust-lang#118212. r? @petrochenkov

…uwer Rollup of 8 pull requests Successful merges: - #150075 (Implement clamp_to) - #156716 (tests: fix: parallel frontend test failures: different alloc ids) - #158397 (delegation: support simplest output `Self` mapping) - #158613 (Fix getrandom fallback test on platforms with `panic=abort`) - #158620 (Remove skip_norm_w/i/p().def_id with a helper) - #158633 (Remove unnecessary `Clone` derives on resolver types) - #158634 (Add missing `needs_drop` check to `DroplessArena`.) - #158647 (Document `strip_circumfix` behavior on overlapping prefix and suffix.)

…uwer Rollup of 8 pull requests Successful merges: - #158294 (Use .drectve for MSVC DLL exports) - #156716 (tests: fix: parallel frontend test failures: different alloc ids) - #158397 (delegation: support simplest output `Self` mapping) - #158613 (Fix getrandom fallback test on platforms with `panic=abort`) - #158620 (Remove skip_norm_w/i/p().def_id with a helper) - #158633 (Remove unnecessary `Clone` derives on resolver types) - #158634 (Add missing `needs_drop` check to `DroplessArena`.) - #158647 (Document `strip_circumfix` behavior on overlapping prefix and suffix.)

@petrochenkov

Rollup merge of #158397 - aerooneqq:delegation-self-type-mapping, r=petrochenkov delegation: support simplest output `Self` mapping This PR supports simplest output `Self` mapping for callee path if the following conditions are met (see `should_wrap_return_value`). Example: ```rust trait Trait { fn method(&self) -> Self; fn r#static() -> Self; fn raw_S(&self) -> S { S } } struct S; impl Trait for S { fn method(&self) -> S { S } fn r#static() -> S { S } } struct W(S); impl Trait for W { #[attr = Inline(Hint)] fn method(self: _) -> _ { Self { 0: Trait::method(self.0) } } #[attr = Inline(Hint)] fn r#static() -> _ { Trait::r#static() } //~^ WARN: function cannot return without recursing [unconditional_recursion] #[attr = Inline(Hint)] fn raw_S(self: _) -> _ { Trait::raw_S(self.0) } } impl W { #[attr = Inline(Hint)] fn method(self: _) -> _ { Self { 0: Trait::method(self.0) } } #[attr = Inline(Hint)] fn r#static() -> _ { Trait::r#static() } #[attr = Inline(Hint)] fn raw_S(self: _) -> _ { Trait::raw_S(self.0) } } ``` ~If the above conditions are met, there is no need to propagate generics of a newtype, as unused generics is an error, thus they should be used in a single field and it can be inferred from the return type of callee path.~ ~Accessing signatures through queries produced query cycles in one test, so `with_no_trimmed_paths` was used to prevent it, though it can cause other cycles in other situations maybe.~ Part of #118212. r? @petrochenkov

rustbot assigned petrochenkov Jun 25, 2026

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 Jun 25, 2026

petrochenkov added the F-fn_delegation `#![feature(fn_delegation)]` label Jun 25, 2026

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aerooneqq mentioned this pull request Jun 26, 2026

delegation: refactor AST -> HIR lowering #158434

Merged

aerooneqq force-pushed the delegation-self-type-mapping branch from d1508f4 to 71a5c95 Compare June 29, 2026 14:28

petrochenkov reviewed Jun 29, 2026

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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 Jun 29, 2026

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 Jul 1, 2026

petrochenkov reviewed Jul 1, 2026

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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 Jul 1, 2026

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 Jul 1, 2026

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Comment thread compiler/rustc_ast_lowering/src/delegation.rs Outdated

rustbot removed the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Jul 1, 2026

aerooneqq changed the title ~~delegation: support simplest newtype wrapping~~ delegation: support simplest output Self mapping Jul 1, 2026

Support simplest output Self mapping in delegation

92c10f9

aerooneqq force-pushed the delegation-self-type-mapping branch from ee6cfed to 92c10f9 Compare July 1, 2026 12:37

rust-bors Bot added the S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. label Jul 1, 2026

JonathanBrouwer mentioned this pull request Jul 1, 2026

Rollup of 8 pull requests #158660

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JonathanBrouwer mentioned this pull request Jul 1, 2026

Rollup of 8 pull requests #158661

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JonathanBrouwer mentioned this pull request Jul 1, 2026

Rollup of 8 pull requests #158663

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rust-bors Bot merged commit aad6334 into rust-lang:main Jul 1, 2026
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rustbot added this to the 1.98.0 milestone Jul 1, 2026

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delegation: support simplest output `Self` mapping - #158397

delegation: support simplest output `Self` mapping#158397
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