Support default-body trait functions with return-position `impl Trait` in traits #101679

compiler-errors · 2022-09-11T08:11:45Z

Introduce a new Trait candidate kind for the ImplTraitInTrait projection candidate, which just projects an RPITIT down to its opaque type form.

This is a hack until we lower RPITITs to regular associated types, after which we will need to rework how these default bodies are type-checked, so comments are left in a few places for us to clean up later.

Fixes #101665

rust-highfive · 2022-09-11T08:11:48Z

r? @jackh726

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…1-dead Only encode return-position `impl Trait` in trait when parent function has a default body Semi-blocked on rust-lang#101679, because I can't currently write a test for when we _should_ encode the type of the return-position `impl Trait` in trait, which is when a trait has a default function body, like so: ```rust trait Foo { fn bar() -> impl Sized { } } ``` Though this can land even without rust-lang#101679, since it does prevent ICEs from occuring any time you use `#![feature(return_position_impl_trait_in_trait)]` in a library, which is kind annoying.

bors · 2022-09-24T09:44:31Z

☔ The latest upstream changes (presumably #102223) made this pull request unmergeable. Please resolve the merge conflicts.

nikomatsakis · 2022-09-30T16:57:59Z

r=me, but needs rebase

bors · 2022-10-03T20:53:36Z

☔ The latest upstream changes (presumably #102627) made this pull request unmergeable. Please resolve the merge conflicts.

compiler-errors · 2022-10-05T03:00:27Z

I added 7a1f25e0569c6ca5fb3d3c8fa05aa3202235d36d which actually makes sure the default body satisfies the RPIT bounds, and doesn't normalize unless there's a default body.
I added a test for default-body async fn in trait with impl Trait return fails to compile #102688 which fails to compile even with this PR. That requires #![feature(return_position_impl_trait_in_trait)], so I still want to land this since it fixes the AFIT case which we're more likely to stabilize sooner.
- The root cause for this test failure is the same as Fn trait doesn't allow impl returns (impl Fn() -> impl Trait), which is inconsistent with all other traits #101968 (comment), so it's not an RPITIT/AFIT issue specifically.

…dy is provided

nikomatsakis · 2022-10-12T16:53:17Z

@bors r+

bors · 2022-10-12T16:53:19Z

📌 Commit 0eeeea9 has been approved by nikomatsakis

It is now in the queue for this repository.

bors · 2022-10-12T21:03:50Z

⌛ Testing commit 0eeeea9 with merge 0938e16...

bors · 2022-10-13T00:09:25Z

☀️ Test successful - checks-actions
Approved by: nikomatsakis
Pushing 0938e16 to master...

rust-timer · 2022-10-13T01:29:11Z

Finished benchmarking commit (0938e16): comparison URL.

Overall result: ✅ improvements - no action needed

@rustbot label: -perf-regression

Instruction count

This is a highly reliable metric that was used to determine the overall result at the top of this comment.

	mean¹	range	count²
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.7%	[-0.9%, -0.6%]	6
Improvements ✅ (secondary)	-0.6%	[-0.8%, -0.3%]	3
All ❌✅ (primary)	-0.7%	[-0.9%, -0.6%]	6

Max RSS (memory usage)

This benchmark run did not return any relevant results for this metric.

Cycles

Results

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean¹	range	count²
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-2.5%	[-2.5%, -2.5%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-2.5%	[-2.5%, -2.5%]	1

the arithmetic mean of the percent change ↩ ↩²
number of relevant changes ↩ ↩²

Mark-Simulacrum · 2022-10-18T12:55:28Z

Improvements look to be at least mostly driven by diesel, which is in its (new) noise range. Can likely be ignored.

… r=nikomatsakis Support default-body trait functions with return-position `impl Trait` in traits Introduce a new `Trait` candidate kind for the `ImplTraitInTrait` projection candidate, which just projects an RPITIT down to its opaque type form. This is a hack until we lower RPITITs to regular associated types, after which we will need to rework how these default bodies are type-checked, so comments are left in a few places for us to clean up later. Fixes rust-lang#101665

rust-highfive assigned jackh726 Sep 11, 2022

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

rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Sep 11, 2022

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compiler-errors force-pushed the rpitit-default-body branch from 6ea3e43 to 9be7558 Compare September 11, 2022 08:18

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compiler-errors mentioned this pull request Sep 11, 2022

Only encode return-position impl Trait in trait when parent function has a default body #101682

Merged

compiler-errors added the F-return_position_impl_trait_in_trait `#![feature(return_position_impl_trait_in_trait)]` label Sep 12, 2022

compiler-errors mentioned this pull request Sep 26, 2022

async fn in trait: trait method with default impl doesn't work #102308

Closed

nikomatsakis approved these changes Sep 30, 2022

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compiler-errors force-pushed the rpitit-default-body branch from 576805e to 4717748 Compare October 2, 2022 02:40

Support default-body trait functions with RPITIT

21047f1

compiler-errors force-pushed the rpitit-default-body branch from 4717748 to 7a1f25e Compare October 5, 2022 02:45

compiler-errors mentioned this pull request Oct 5, 2022

default-body async fn in trait with impl Trait return fails to compile #102688

Closed

compiler-errors requested a review from nikomatsakis October 5, 2022 03:00

compiler-errors added 3 commits October 5, 2022 04:16

Fix test for default body with impl

7945036

Bless tests

86734b0

Validate opaques in default trait bodies, don't normalize unless a bo…

9a5936b

…dy is provided

compiler-errors force-pushed the rpitit-default-body branch from caf86ca to 67b5f32 Compare October 5, 2022 04:16

This was referenced Oct 9, 2022

ICE using return_position_impl_trait_in_trait with default implementation #102826

Closed

failed to get output type of async function #102965

Closed

Add broken test for AFIT with RPITIT

0eeeea9

compiler-errors force-pushed the rpitit-default-body branch from 67b5f32 to 0eeeea9 Compare October 12, 2022 16:34

nikomatsakis approved these changes Oct 12, 2022

View reviewed changes

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 Oct 12, 2022

bors added the merged-by-bors This PR was explicitly merged by bors. label Oct 13, 2022

bors merged commit 0938e16 into rust-lang:master Oct 13, 2022

rustbot added this to the 1.66.0 milestone Oct 13, 2022

bors mentioned this pull request Oct 13, 2022

split async-trait-fn test into working and not-yet working parts #102213

Closed

tmandry mentioned this pull request Nov 1, 2022

Tracking Issue for async_fn_in_trait, return_position_impl_trait_in_trait #91611

Closed

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compiler-errors deleted the rpitit-default-body branch November 2, 2022 02:58

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Support default-body trait functions with return-position `impl Trait` in traits #101679

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Overall result: ✅ improvements - no action needed

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Support default-body trait functions with return-position `impl Trait` in traits #101679

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