Rollup merge of rust-lang#63383 - Centril:async-lifetime-elision-tests, r=nikomatsakis

`async fn` lifetime elision tests

Add `async fn` version of the tests in rust-lang#61207 per the first checkbox in rust-lang#62121 (comment).
Works towards resolving blockers in rust-lang#63209.

r? @nikomatsakis
cc @cramertj

Author: Centril

src/test/ui/self/arbitrary_self_types_pin_lifetime-async.rs

@@ -0,0 +1,37 @@
+// check-pass
+// edition:2018
+
+#![feature(async_await)]
+
+use std::pin::Pin;
+use std::task::{Context, Poll};
+
+struct Foo;
+
+impl Foo {
+    async fn pin_ref(self: Pin<&Self>) -> Pin<&Self> { self }
+
+    async fn pin_mut(self: Pin<&mut Self>) -> Pin<&mut Self> { self }
+
+    async fn pin_pin_pin_ref(self: Pin<Pin<Pin<&Self>>>) -> Pin<Pin<Pin<&Self>>> { self }
+
+    async fn pin_ref_impl_trait(self: Pin<&Self>) -> impl Clone + '_ { self }
+
+    fn b(self: Pin<&Foo>, f: &Foo) -> Pin<&Foo> { self }
+}
+
+type Alias<T> = Pin<T>;
+impl Foo {
+    async fn bar<'a>(self: Alias<&Self>, arg: &'a ()) -> Alias<&Self> { self }
+}
+
+// FIXME(Centril): extend with the rest of the non-`async fn` test
+// when we allow `async fn`s inside traits and trait implementations.
+
+fn main() {
+    let mut foo = Foo;
+    { Pin::new(&foo).pin_ref() };
+    { Pin::new(&mut foo).pin_mut() };
+    { Pin::new(Pin::new(Pin::new(&foo))).pin_pin_pin_ref() };
+    { Pin::new(&foo).pin_ref_impl_trait() };
+}

src/test/ui/self/arbitrary_self_types_pin_lifetime_impl_trait-async.nll.stderr

@@ -0,0 +1,14 @@
+error: lifetime may not live long enough
+  --> $DIR/arbitrary_self_types_pin_lifetime_impl_trait-async.rs:10:48
+   |
+LL |     async fn f(self: Pin<&Self>) -> impl Clone { self }
+   |                          -                     ^^^^^^^^ returning this value requires that `'_` must outlive `'static`
+   |                          |
+   |                          lifetime `'_` defined here
+help: to allow this `impl Trait` to capture borrowed data with lifetime `'_`, add `'_` as a constraint
+   |
+LL |     async fn f(self: Pin<&Self>) -> impl Clone + '_ { self }
+   |                                     ^^^^^^^^^^^^^^^
+
+error: aborting due to previous error
+

src/test/ui/self/arbitrary_self_types_pin_lifetime_impl_trait-async.rs

@@ -0,0 +1,16 @@
+// edition:2018
+
+#![feature(async_await)]
+
+use std::pin::Pin;
+
+struct Foo;
+
+impl Foo {
+    async fn f(self: Pin<&Self>) -> impl Clone { self }
+    //~^ ERROR cannot infer an appropriate lifetime
+}
+
+fn main() {
+    { Pin::new(&Foo).f() };
+}

src/test/ui/self/arbitrary_self_types_pin_lifetime_impl_trait-async.stderr

@@ -0,0 +1,20 @@
+error: cannot infer an appropriate lifetime
+  --> $DIR/arbitrary_self_types_pin_lifetime_impl_trait-async.rs:10:16
+   |
+LL |     async fn f(self: Pin<&Self>) -> impl Clone { self }
+   |                ^^^^                 ---------- this return type evaluates to the `'static` lifetime...
+   |                |
+   |                ...but this borrow...
+   |
+note: ...can't outlive the lifetime '_ as defined on the method body at 10:26
+  --> $DIR/arbitrary_self_types_pin_lifetime_impl_trait-async.rs:10:26
+   |
+LL |     async fn f(self: Pin<&Self>) -> impl Clone { self }
+   |                          ^
+help: you can add a constraint to the return type to make it last less than `'static` and match the lifetime '_ as defined on the method body at 10:26
+   |
+LL |     async fn f(self: Pin<&Self>) -> impl Clone + '_ { self }
+   |                                     ^^^^^^^^^^^^^^^
+
+error: aborting due to previous error
+

src/test/ui/self/arbitrary_self_types_pin_lifetime_mismatch-async.nll.stderr

@@ -0,0 +1,27 @@
+error[E0106]: missing lifetime specifier
+  --> $DIR/arbitrary_self_types_pin_lifetime_mismatch-async.rs:10:45
+   |
+LL |     async fn a(self: Pin<&Foo>, f: &Foo) -> &Foo { f }
+   |                                             ^
+   |
+   = note: return-position elided lifetimes require exactly one input-position elided lifetime, found multiple.
+
+error[E0106]: missing lifetime specifier
+  --> $DIR/arbitrary_self_types_pin_lifetime_mismatch-async.rs:15:60
+   |
+LL |     async fn c(self: Pin<&Self>, f: &Foo, g: &Foo) -> (Pin<&Foo>, &Foo) { (self, f) }
+   |                                                            ^
+   |
+   = note: return-position elided lifetimes require exactly one input-position elided lifetime, found multiple.
+
+error[E0106]: missing lifetime specifier
+  --> $DIR/arbitrary_self_types_pin_lifetime_mismatch-async.rs:15:67
+   |
+LL |     async fn c(self: Pin<&Self>, f: &Foo, g: &Foo) -> (Pin<&Foo>, &Foo) { (self, f) }
+   |                                                                   ^
+   |
+   = note: return-position elided lifetimes require exactly one input-position elided lifetime, found multiple.
+
+error: aborting due to 3 previous errors
+
+For more information about this error, try `rustc --explain E0106`.

src/test/ui/self/arbitrary_self_types_pin_lifetime_mismatch-async.rs

@@ -0,0 +1,28 @@
+// edition:2018
+
+#![feature(async_await)]
+
+use std::pin::Pin;
+
+struct Foo;
+
+impl Foo {
+    async fn a(self: Pin<&Foo>, f: &Foo) -> &Foo { f }
+    //~^ ERROR missing lifetime specifier
+    //~| ERROR cannot infer an appropriate lifetime
+    // FIXME: should be E0623?
+
+    async fn c(self: Pin<&Self>, f: &Foo, g: &Foo) -> (Pin<&Foo>, &Foo) { (self, f) }
+    //~^ ERROR missing lifetime specifier
+    //~| ERROR cannot infer an appropriate lifetime
+    //~| ERROR missing lifetime specifier
+    //~| ERROR cannot infer an appropriate lifetime
+    // FIXME: should be E0623?
+}
+
+type Alias<T> = Pin<T>;
+impl Foo {
+    async fn bar<'a>(self: Alias<&Self>, arg: &'a ()) -> &() { arg } //~ ERROR E0623
+}
+
+fn main() {}

src/test/ui/self/arbitrary_self_types_pin_lifetime_mismatch-async.stderr

@@ -0,0 +1,88 @@
+error[E0106]: missing lifetime specifier
+  --> $DIR/arbitrary_self_types_pin_lifetime_mismatch-async.rs:10:45
+   |
+LL |     async fn a(self: Pin<&Foo>, f: &Foo) -> &Foo { f }
+   |                                             ^
+   |
+   = note: return-position elided lifetimes require exactly one input-position elided lifetime, found multiple.
+
+error[E0106]: missing lifetime specifier
+  --> $DIR/arbitrary_self_types_pin_lifetime_mismatch-async.rs:15:60
+   |
+LL |     async fn c(self: Pin<&Self>, f: &Foo, g: &Foo) -> (Pin<&Foo>, &Foo) { (self, f) }
+   |                                                            ^
+   |
+   = note: return-position elided lifetimes require exactly one input-position elided lifetime, found multiple.
+
+error[E0106]: missing lifetime specifier
+  --> $DIR/arbitrary_self_types_pin_lifetime_mismatch-async.rs:15:67
+   |
+LL |     async fn c(self: Pin<&Self>, f: &Foo, g: &Foo) -> (Pin<&Foo>, &Foo) { (self, f) }
+   |                                                                   ^
+   |
+   = note: return-position elided lifetimes require exactly one input-position elided lifetime, found multiple.
+
+error: cannot infer an appropriate lifetime
+  --> $DIR/arbitrary_self_types_pin_lifetime_mismatch-async.rs:10:33
+   |
+LL |     async fn a(self: Pin<&Foo>, f: &Foo) -> &Foo { f }
+   |                                 ^           ---- this return type evaluates to the `'static` lifetime...
+   |                                 |
+   |                                 ...but this borrow...
+   |
+note: ...can't outlive the lifetime '_ as defined on the method body at 10:26
+  --> $DIR/arbitrary_self_types_pin_lifetime_mismatch-async.rs:10:26
+   |
+LL |     async fn a(self: Pin<&Foo>, f: &Foo) -> &Foo { f }
+   |                          ^
+help: you can add a constraint to the return type to make it last less than `'static` and match the lifetime '_ as defined on the method body at 10:26
+   |
+LL |     async fn a(self: Pin<&Foo>, f: &Foo) -> &Foo + '_ { f }
+   |                                             ^^^^^^^^^
+
+error: cannot infer an appropriate lifetime
+  --> $DIR/arbitrary_self_types_pin_lifetime_mismatch-async.rs:15:16
+   |
+LL |     async fn c(self: Pin<&Self>, f: &Foo, g: &Foo) -> (Pin<&Foo>, &Foo) { (self, f) }
+   |                ^^^^ ...but this borrow...             ----------------- this return type evaluates to the `'static` lifetime...
+   |
+note: ...can't outlive the lifetime '_ as defined on the method body at 15:26
+  --> $DIR/arbitrary_self_types_pin_lifetime_mismatch-async.rs:15:26
+   |
+LL |     async fn c(self: Pin<&Self>, f: &Foo, g: &Foo) -> (Pin<&Foo>, &Foo) { (self, f) }
+   |                          ^
+help: you can add a constraint to the return type to make it last less than `'static` and match the lifetime '_ as defined on the method body at 15:26
+   |
+LL |     async fn c(self: Pin<&Self>, f: &Foo, g: &Foo) -> (Pin<&Foo>, &Foo) + '_ { (self, f) }
+   |                                                       ^^^^^^^^^^^^^^^^^^^^^^
+
+error: cannot infer an appropriate lifetime
+  --> $DIR/arbitrary_self_types_pin_lifetime_mismatch-async.rs:15:34
+   |
+LL |     async fn c(self: Pin<&Self>, f: &Foo, g: &Foo) -> (Pin<&Foo>, &Foo) { (self, f) }
+   |                                  ^                    ----------------- this return type evaluates to the `'static` lifetime...
+   |                                  |
+   |                                  ...but this borrow...
+   |
+note: ...can't outlive the lifetime '_ as defined on the method body at 15:26
+  --> $DIR/arbitrary_self_types_pin_lifetime_mismatch-async.rs:15:26
+   |
+LL |     async fn c(self: Pin<&Self>, f: &Foo, g: &Foo) -> (Pin<&Foo>, &Foo) { (self, f) }
+   |                          ^
+help: you can add a constraint to the return type to make it last less than `'static` and match the lifetime '_ as defined on the method body at 15:26
+   |
+LL |     async fn c(self: Pin<&Self>, f: &Foo, g: &Foo) -> (Pin<&Foo>, &Foo) + '_ { (self, f) }
+   |                                                       ^^^^^^^^^^^^^^^^^^^^^^
+
+error[E0623]: lifetime mismatch
+  --> $DIR/arbitrary_self_types_pin_lifetime_mismatch-async.rs:25:58
+   |
+LL |     async fn bar<'a>(self: Alias<&Self>, arg: &'a ()) -> &() { arg }
+   |                                  -----                   ^^^
+   |                                  |                       |
+   |                                  |                       ...but data from `arg` is returned here
+   |                                  this parameter and the return type are declared with different lifetimes...
+
+error: aborting due to 7 previous errors
+
+For more information about this error, try `rustc --explain E0106`.

src/test/ui/self/elision/README.md

@@ -42,3 +42,34 @@ In each case, we test the following patterns:
 - `self: Box<Pin<XXX>>`
 
 In the non-reference cases, `Pin` causes errors so we substitute `Rc`.
+
+### `async fn`
+
+For each of the tests above we also check that `async fn` behaves as an `fn` would.
+These tests are in files named `*-async.rs`.
+
+Legends:
+- ✓ ⟹ Yes / Pass
+- X ⟹ No
+- α ⟹ lifetime mismatch
+- β ⟹ cannot infer an appropriate lifetime
+- γ ⟹ missing lifetime specifier
+
+| `async` file | Pass? | Conforms to `fn`? | How does it diverge? <br/> `fn` ⟶ `async fn` |
+| --- | --- | --- | --- |
+| `self-async.rs` | ✓ | ✓ | N/A |
+| `struct-async.rs`| ✓ | ✓ | N/A |
+| `alias-async.rs`| ✓ | ✓ | N/A |
+| `assoc-async.rs`| ✓ | ✓ | N/A |
+| `ref-self-async.rs` | X | X | α ⟶ β + γ |
+| `ref-mut-self-async.rs` | X | X | α ⟶ β + γ |
+| `ref-struct-async.rs` | X | X | α ⟶ β + γ |
+| `ref-mut-struct-async.rs` | X | X | α ⟶ β + γ |
+| `ref-alias-async.rs` | X | X | ✓ ⟶ β + γ |
+| `ref-assoc-async.rs` | X | X | ✓ ⟶ β + γ |
+| `ref-mut-alias-async.rs` | X | X | ✓ ⟶ β + γ |
+| `lt-self-async.rs` | ✓ | ✓ | N/A
+| `lt-struct-async.rs` | ✓ | ✓ | N/A
+| `lt-alias-async.rs` | ✓ | ✓ | N/A
+| `lt-assoc-async.rs` | ✓ | ✓ | N/A
+| `lt-ref-self-async.rs` | X | X | α ⟶ β + γ

src/test/ui/self/elision/alias-async.rs

@@ -0,0 +1,39 @@
+// check-pass
+// edition:2018
+
+#![feature(async_await)]
+
+#![feature(arbitrary_self_types)]
+#![allow(non_snake_case)]
+
+use std::rc::Rc;
+
+struct Struct { }
+
+type Alias = Struct;
+
+impl Struct {
+    // Test using an alias for `Struct`:
+
+    async fn alias(self: Alias, f: &u32) -> &u32 {
+        f
+    }
+
+    async fn box_Alias(self: Box<Alias>, f: &u32) -> &u32 {
+        f
+    }
+
+    async fn rc_Alias(self: Rc<Alias>, f: &u32) -> &u32 {
+        f
+    }
+
+    async fn box_box_Alias(self: Box<Box<Alias>>, f: &u32) -> &u32 {
+        f
+    }
+
+    async fn box_rc_Alias(self: Box<Rc<Alias>>, f: &u32) -> &u32 {
+        f
+    }
+}
+
+fn main() { }

src/test/ui/self/elision/assoc-async.rs

@@ -0,0 +1,43 @@
+// check-pass
+// edition:2018
+
+#![feature(async_await)]
+
+#![feature(arbitrary_self_types)]
+#![allow(non_snake_case)]
+
+use std::rc::Rc;
+
+trait Trait {
+    type AssocType;
+}
+
+struct Struct { }
+
+impl Trait for Struct {
+    type AssocType = Self;
+}
+
+impl Struct {
+    async fn assoc(self: <Struct as Trait>::AssocType, f: &u32) -> &u32 {
+        f
+    }
+
+    async fn box_AssocType(self: Box<<Struct as Trait>::AssocType>, f: &u32) -> &u32 {
+        f
+    }
+
+    async fn rc_AssocType(self: Rc<<Struct as Trait>::AssocType>, f: &u32) -> &u32 {
+        f
+    }
+
+    async fn box_box_AssocType(self: Box<Box<<Struct as Trait>::AssocType>>, f: &u32) -> &u32 {
+        f
+    }
+
+    async fn box_rc_AssocType(self: Box<Rc<<Struct as Trait>::AssocType>>, f: &u32) -> &u32 {
+        f
+    }
+}
+
+fn main() { }

src/test/ui/self/elision/lt-alias-async.rs

@@ -0,0 +1,41 @@
+// check-pass
+// edition:2018
+
+#![feature(async_await)]
+
+#![feature(arbitrary_self_types)]
+#![allow(non_snake_case)]
+
+use std::rc::Rc;
+
+struct Struct<'a> { x: &'a u32 }
+
+type Alias<'a> = Struct<'a>;
+
+impl<'a> Alias<'a> {
+    async fn take_self(self, f: &u32) -> &u32 {
+        f
+    }
+
+    async fn take_Alias(self: Alias<'a>, f: &u32) -> &u32 {
+        f
+    }
+
+    async fn take_Box_Alias(self: Box<Alias<'a>>, f: &u32) -> &u32 {
+        f
+    }
+
+    async fn take_Box_Box_Alias(self: Box<Box<Alias<'a>>>, f: &u32) -> &u32 {
+        f
+    }
+
+    async fn take_Rc_Alias(self: Rc<Alias<'a>>, f: &u32) -> &u32 {
+        f
+    }
+
+    async fn take_Box_Rc_Alias(self: Box<Rc<Alias<'a>>>, f: &u32) -> &u32 {
+        f
+    }
+}
+
+fn main() { }