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Restore impl Future<Output = Type> to async blocks #95263

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Mar 31, 2022
Merged

Restore impl Future<Output = Type> to async blocks #95263

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27 changes: 20 additions & 7 deletions compiler/rustc_middle/src/ty/print/pretty.rs
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Expand Up @@ -912,12 +912,25 @@ pub trait PrettyPrinter<'tcx>:
}

for (assoc_item_def_id, term) in assoc_items {
// Skip printing `<[generator@] as Generator<_>>::Return` from async blocks
if let Some(ty) = term.skip_binder().ty() &&
let ty::Projection(ty::ProjectionTy { item_def_id, .. }) = ty.kind() &&
Some(*item_def_id) == self.tcx().lang_items().generator_return() {
continue;
}
// Skip printing `<[generator@] as Generator<_>>::Return` from async blocks,
// unless we can find out what generator return type it comes from.
Comment on lines +915 to +916
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Seems to say the inverse of what it should say

Suggested change
// Skip printing `<[generator@] as Generator<_>>::Return` from async blocks,
// unless we can find out what generator return type it comes from.
// Skip printing `<[generator@] as Generator<_>>::Return` from async blocks
// if we can find out what generator return type it comes from.

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@compiler-errors compiler-errors Mar 30, 2022 •
edited
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Maybe our perspectives are inverted -- so it does two things, 1. skips printing <[generator@] as Generator<_>>::Return regardless, but 2. will instead print Output=Type if it can find the return type. If it can't, it skips printing altogether.

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Oh, then the comment makes sense 👍🏼

let term = if let Some(ty) = term.skip_binder().ty()
&& let ty::Projection(ty::ProjectionTy { item_def_id, substs }) = ty.kind()
&& Some(*item_def_id) == self.tcx().lang_items().generator_return()
{
if let ty::Generator(_, substs, _) = substs.type_at(0).kind() {
let return_ty = substs.as_generator().return_ty();
if !return_ty.is_ty_infer() {
return_ty.into()
} else {
continue;
}
} else {
continue;
}
} else {
term.skip_binder()
};

if first {
p!("<");
Expand All @@ -928,7 +941,7 @@ pub trait PrettyPrinter<'tcx>:

p!(write("{} = ", self.tcx().associated_item(assoc_item_def_id).name));

match term.skip_binder() {
match term {
Term::Ty(ty) => {
p!(print(ty))
}
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2 changes: 1 addition & 1 deletion src/test/ui/async-await/async-block-control-flow-static-semantics.rs
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Expand Up @@ -24,7 +24,7 @@ async fn return_targets_async_block_not_async_fn() -> u8 {
return 0u8;
};
let _: &dyn Future<Output = ()> = &block;
//~^ ERROR type mismatch resolving `<impl Future as Future>::Output == ()`
//~^ ERROR type mismatch resolving `<impl Future<Output = u8> as Future>::Output == ()`
}

fn no_break_in_async_block() {
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4 changes: 2 additions & 2 deletions src/test/ui/async-await/async-block-control-flow-static-semantics.stderr
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Expand Up @@ -31,7 +31,7 @@ LL | |
LL | | }
| |_^ expected `u8`, found `()`

error[E0271]: type mismatch resolving `<impl Future as Future>::Output == ()`
error[E0271]: type mismatch resolving `<impl Future<Output = u8> as Future>::Output == ()`
--> $DIR/async-block-control-flow-static-semantics.rs:26:39
|
LL | let _: &dyn Future<Output = ()> = &block;
Expand All @@ -47,7 +47,7 @@ LL | fn return_targets_async_block_not_fn() -> u8 {
| |
| implicitly returns `()` as its body has no tail or `return` expression

error[E0271]: type mismatch resolving `<impl Future as Future>::Output == ()`
error[E0271]: type mismatch resolving `<impl Future<Output = u8> as Future>::Output == ()`
--> $DIR/async-block-control-flow-static-semantics.rs:17:39
|
LL | let _: &dyn Future<Output = ()> = &block;
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4 changes: 2 additions & 2 deletions src/test/ui/async-await/generator-desc.stderr
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Expand Up @@ -46,8 +46,8 @@ LL | pub const fn from_generator<T>(gen: T) -> impl Future<Output = T::Return>
| the expected opaque type
| the found opaque type
|
= note: expected opaque type `impl Future` (`async` closure body)
found opaque type `impl Future` (`async` closure body)
= note: expected opaque type `impl Future<Output = ()>` (`async` closure body)
found opaque type `impl Future<Output = ()>` (`async` closure body)

error: aborting due to 3 previous errors

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2 changes: 1 addition & 1 deletion src/test/ui/async-await/issue-67252-unnamed-future.stderr
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Expand Up @@ -4,7 +4,7 @@ error: future cannot be sent between threads safely
LL | spawn(async {
| ^^^^^ future created by async block is not `Send`
|
= help: within `impl Future`, the trait `Send` is not implemented for `*mut ()`
= help: within `impl Future<Output = ()>`, the trait `Send` is not implemented for `*mut ()`
note: future is not `Send` as this value is used across an await
--> $DIR/issue-67252-unnamed-future.rs:20:16
|
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4 changes: 2 additions & 2 deletions src/test/ui/async-await/issue-68112.stderr
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Expand Up @@ -44,13 +44,13 @@ LL | require_send(send_fut);
= note: required because of the requirements on the impl of `Send` for `Arc<RefCell<i32>>`
= note: required because it appears within the type `[static generator@$DIR/issue-68112.rs:47:31: 47:36]`
= note: required because it appears within the type `from_generator::GenFuture<[static generator@$DIR/issue-68112.rs:47:31: 47:36]>`
= note: required because it appears within the type `impl Future`
= note: required because it appears within the type `impl Future<Output = Arc<RefCell<i32>>>`
= note: required because it appears within the type `impl Future<Output = Arc<RefCell<i32>>>`
= note: required because it appears within the type `impl Future<Output = Arc<RefCell<i32>>>`
= note: required because it appears within the type `{ResumeTy, impl Future<Output = Arc<RefCell<i32>>>, (), i32, Ready<i32>}`
= note: required because it appears within the type `[static generator@$DIR/issue-68112.rs:55:26: 59:6]`
= note: required because it appears within the type `from_generator::GenFuture<[static generator@$DIR/issue-68112.rs:55:26: 59:6]>`
= note: required because it appears within the type `impl Future`
= note: required because it appears within the type `impl Future<Output = ()>`
note: required by a bound in `require_send`
--> $DIR/issue-68112.rs:11:25
|
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2 changes: 1 addition & 1 deletion src/test/ui/async-await/issues/issue-65436-raw-ptr-not-send.stderr
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Expand Up @@ -4,7 +4,7 @@ error: future cannot be sent between threads safely
LL | assert_send(async {
| ^^^^^^^^^^^ future created by async block is not `Send`
|
= help: within `impl Future`, the trait `Send` is not implemented for `*const u8`
= help: within `impl Future<Output = ()>`, the trait `Send` is not implemented for `*const u8`
note: future is not `Send` as this value is used across an await
--> $DIR/issue-65436-raw-ptr-not-send.rs:14:35
|
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2 changes: 1 addition & 1 deletion src/test/ui/async-await/partial-drop-partial-reinit.stderr
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Expand Up @@ -14,7 +14,7 @@ LL | async fn foo() {
= note: required because it appears within the type `{ResumeTy, (NotSend,), impl Future<Output = ()>, ()}`
= note: required because it appears within the type `[static generator@$DIR/partial-drop-partial-reinit.rs:22:16: 27:2]`
= note: required because it appears within the type `from_generator::GenFuture<[static generator@$DIR/partial-drop-partial-reinit.rs:22:16: 27:2]>`
= note: required because it appears within the type `impl Future`
= note: required because it appears within the type `impl Future<Output = ()>`
= note: required because it appears within the type `impl Future<Output = ()>`
note: required by a bound in `gimme_send`
--> $DIR/partial-drop-partial-reinit.rs:10:18
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2 changes: 1 addition & 1 deletion src/test/ui/chalkify/bugs/async.stderr
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Expand Up @@ -28,7 +28,7 @@ note: required by a bound in `from_generator`
LL | T: Generator<ResumeTy, Yield = ()>,
| ^^^^^^^^^^ required by this bound in `from_generator`

error[E0280]: the requirement `<impl Future as Future>::Output == u32` is not satisfied
error[E0280]: the requirement `<impl Future<Output = u32> as Future>::Output == u32` is not satisfied
--> $DIR/async.rs:7:29
|
LL | async fn foo(x: u32) -> u32 {
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2 changes: 1 addition & 1 deletion src/test/ui/impl-trait/issue-55872-3.rs
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Expand Up @@ -13,7 +13,7 @@ impl<S> Bar for S {
type E = impl std::marker::Copy;
fn foo<T>() -> Self::E {
async {}
//~^ ERROR the trait bound `impl Future: Copy` is not satisfied [E0277]
//~^ ERROR the trait bound `impl Future<Output = ()>: Copy` is not satisfied [E0277]
}
}

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4 changes: 2 additions & 2 deletions src/test/ui/impl-trait/issue-55872-3.stderr
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@@ -1,8 +1,8 @@
error[E0277]: the trait bound `impl Future: Copy` is not satisfied
error[E0277]: the trait bound `impl Future<Output = ()>: Copy` is not satisfied
--> $DIR/issue-55872-3.rs:15:9
|
LL | async {}
| ^^^^^^^^ the trait `Copy` is not implemented for `impl Future`
| ^^^^^^^^ the trait `Copy` is not implemented for `impl Future<Output = ()>`

error: aborting due to previous error

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2 changes: 1 addition & 1 deletion src/test/ui/impl-trait/issues/issue-78722.stderr
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Expand Up @@ -16,7 +16,7 @@ LL | let f: F = async { 1 };
LL | }],
| - value is dropped here

error[E0271]: type mismatch resolving `<impl Future as Future>::Output == u8`
error[E0271]: type mismatch resolving `<impl Future<Output = ()> as Future>::Output == u8`
--> $DIR/issue-78722.rs:10:13
|
LL | async {}
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2 changes: 1 addition & 1 deletion src/test/ui/pattern/non-structural-match-types.stderr
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Expand Up @@ -4,7 +4,7 @@ error: `[closure@$DIR/non-structural-match-types.rs:9:17: 9:22]` cannot be used
LL | const { || {} } => {},
| ^^^^^^^^^^^^^^^

error: `impl Future` cannot be used in patterns
error: `impl Future<Output = ()>` cannot be used in patterns
--> $DIR/non-structural-match-types.rs:12:9
|
LL | const { async {} } => {},
Expand Down