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Descriptive error when users try to combine RPITIT/AFIT with specialization#108551

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compiler-errors:rpitit-bad-spec
Mar 1, 2023
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Descriptive error when users try to combine RPITIT/AFIT with specialization#108551
bors merged 1 commit intorust-lang:masterfrom
compiler-errors:rpitit-bad-spec

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@compiler-errors compiler-errors commented Feb 28, 2023

Previously we failed with some esoteric error like:

error[E0053]: method `foo` has an incompatible type for trait
  --> $DIR/dont-project-to-specializable-projection.rs:14:35
   |
LL |     default async fn foo(_: T) -> &'static str {
   |                                   ^^^^^^^^^^^^ expected associated type, found future
   |
note: type in trait
  --> $DIR/dont-project-to-specializable-projection.rs:10:27
   |
LL |     async fn foo(_: T) -> &'static str;
   |                           ^^^^^^^^^^^^
   = note: expected signature `fn(_) -> impl Future<Output = &'static str>`
              found signature `fn(_) -> impl Future<Output = &'static str>`

Now we error like:

error: async associated function in trait cannot be specialized
  --> $DIR/dont-project-to-specializable-projection.rs:14:5
   |
LL |     default async fn foo(_: T) -> &'static str {
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: specialization behaves in inconsistent and surprising ways with `#![feature(async_fn_in_trait)]`, and for now is disallowed

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rustbot commented Feb 28, 2023

r? @Nilstrieb

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@rustbot 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 Feb 28, 2023
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compiler-errors commented Feb 28, 2023

r? types

@rustbot rustbot assigned oli-obk and unassigned Noratrieb Feb 28, 2023
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compiler-errors commented Feb 28, 2023
View reviewed changes
tests/ui/impl-trait/in-trait/specialization-broken.stderr
@@ -18,6 +18,14 @@ LL | fn bar(&self) -> impl Sized;
= note: expected signature `fn(&U) -> impl Sized`
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@compiler-errors compiler-errors Feb 28, 2023 •
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This fails to be replaced by the other message because we're not actually even assembling a ProjectionCandidate::ImplTraitInTrait here. Oh well, not that big of a deal.

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oli-obk commented Feb 28, 2023

@bors r+ rollup

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bors commented Feb 28, 2023

📌 Commit ecac8fd has been approved by oli-obk

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 Feb 28, 2023
Dylan-DPC added a commit to Dylan-DPC/rust that referenced this pull request Feb 28, 2023
@Dylan-DPC
Rollup merge of rust-lang#108551 - compiler-errors:rpitit-bad-spec, r…
24018a4 
…=oli-obk

Descriptive error when users try to combine RPITIT/AFIT with specialization

Previously we failed with some esoteric error like:

```
error[E0053]: method `foo` has an incompatible type for trait
  --> $DIR/dont-project-to-specializable-projection.rs:14:35
   |
LL |     default async fn foo(_: T) -> &'static str {
   |                                   ^^^^^^^^^^^^ expected associated type, found future
   |
note: type in trait
  --> $DIR/dont-project-to-specializable-projection.rs:10:27
   |
LL |     async fn foo(_: T) -> &'static str;
   |                           ^^^^^^^^^^^^
   = note: expected signature `fn(_) -> impl Future<Output = &'static str>`
              found signature `fn(_) -> impl Future<Output = &'static str>`
```

Now we error like:

```
error: async associated function in trait cannot be specialized
  --> $DIR/dont-project-to-specializable-projection.rs:14:5
   |
LL |     default async fn foo(_: T) -> &'static str {
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: specialization behaves in inconsistent and surprising ways with `#![feature(async_fn_in_trait)]`, and for now is disallowed
```
@Dylan-DPC Dylan-DPC mentioned this pull request Feb 28, 2023
Closed
matthiaskrgr added a commit to matthiaskrgr/rust that referenced this pull request Feb 28, 2023
@matthiaskrgr
Rollup merge of rust-lang#108551 - compiler-errors:rpitit-bad-spec, r…
a91bda5 
…=oli-obk

Descriptive error when users try to combine RPITIT/AFIT with specialization

Previously we failed with some esoteric error like:

```
error[E0053]: method `foo` has an incompatible type for trait
  --> $DIR/dont-project-to-specializable-projection.rs:14:35
   |
LL |     default async fn foo(_: T) -> &'static str {
   |                                   ^^^^^^^^^^^^ expected associated type, found future
   |
note: type in trait
  --> $DIR/dont-project-to-specializable-projection.rs:10:27
   |
LL |     async fn foo(_: T) -> &'static str;
   |                           ^^^^^^^^^^^^
   = note: expected signature `fn(_) -> impl Future<Output = &'static str>`
              found signature `fn(_) -> impl Future<Output = &'static str>`
```

Now we error like:

```
error: async associated function in trait cannot be specialized
  --> $DIR/dont-project-to-specializable-projection.rs:14:5
   |
LL |     default async fn foo(_: T) -> &'static str {
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: specialization behaves in inconsistent and surprising ways with `#![feature(async_fn_in_trait)]`, and for now is disallowed
```
@matthiaskrgr matthiaskrgr mentioned this pull request Feb 28, 2023
Closed
@matthiaskrgr matthiaskrgr mentioned this pull request Mar 1, 2023
Merged
bors added a commit to rust-lang-ci/rust that referenced this pull request Mar 1, 2023
@bors
Auto merge of rust-lang#108586 - matthiaskrgr:rollup-ry9u2ou, r=matth…
5983a3a 
…iaskrgr

Rollup of 8 pull requests

Successful merges:

 - rust-lang#108297 (Exit when there are unmatched delims to avoid noisy diagnostics)
 - rust-lang#108531 (rustdoc: Show that repeated expression arrays can be made with constant values)
 - rust-lang#108536 (Update books)
 - rust-lang#108550 (Remove the `capture_disjoint_fields` feature)
 - rust-lang#108551 (Descriptive error when users try to combine RPITIT/AFIT with specialization)
 - rust-lang#108554 (Only look for param in item's generics if it actually comes from generics)
 - rust-lang#108555 (Fix a race in the query system)
 - rust-lang#108558 (add missing feature in core/tests)

Failed merges:

r? `@ghost`
`@rustbot` modify labels: rollup
@bors bors merged commit b2dc8c5 into rust-lang:master Mar 1, 2023
@rustbot rustbot added this to the 1.69.0 milestone Mar 1, 2023
@compiler-errors compiler-errors deleted the rpitit-bad-spec branch August 11, 2023 20:18
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