introduce more tests covering async fn surface

src/test/ui/async-await/multiple-lifetimes/elided.rs

@@ -0,0 +1,12 @@
+// edition:2018
+// run-pass
+
+// Test that we can use async fns with multiple arbitrary lifetimes.
+
+#![feature(async_await, await_macro)]
+
+async fn multiple_elided_lifetimes(_: &u8, _: &u8) {}
+
+fn main() {
+    let _ = multiple_elided_lifetimes(&22, &44);
+}

src/test/ui/async-await/multiple-lifetimes/fn-ptr.rs

@@ -0,0 +1,14 @@
+// edition:2018
+// run-pass
+
+// Test that we can use async fns with multiple arbitrary lifetimes.
+
+#![feature(arbitrary_self_types, async_await, await_macro)]
+
+async fn multiple_named_lifetimes<'a, 'b>(_: &'a u8, _: &'b u8, _: fn(&u8)) {}
+
+fn gimme(_: &u8) { }
+
+fn main() {
+    let _ = multiple_named_lifetimes(&22, &44, gimme);
+}

src/test/ui/async-await/multiple-lifetimes/hrtb.rs

@@ -4,17 +4,14 @@
 // Test that we can use async fns with multiple arbitrary lifetimes.
 
 #![feature(arbitrary_self_types, async_await, await_macro)]
+#![allow(dead_code)]
 
 use std::ops::Add;
 
-async fn multiple_named_lifetimes<'a, 'b>(_: &'a u8, _: &'b u8) {}
-
 async fn multiple_hrtb_and_single_named_lifetime_ok<'c>(
     _: impl for<'a> Add<&'a u8>,
     _: impl for<'b> Add<&'b u8>,
     _: &'c u8,
 ) {}
 
-async fn multiple_elided_lifetimes(_: &u8, _: &u8) {}
-
 fn main() {}

src/test/ui/async-await/multiple-lifetimes/named.rs

@@ -0,0 +1,12 @@
+// edition:2018
+// run-pass
+
+// Test that we can use async fns with multiple arbitrary lifetimes.
+
+#![feature(arbitrary_self_types, async_await, await_macro)]
+
+async fn multiple_named_lifetimes<'a, 'b>(_: &'a u8, _: &'b u8) {}
+
+fn main() {
+    let _ = multiple_named_lifetimes(&22, &44);
+}

src/test/ui/async-await/multiple-lifetimes/partial-relation.rs

@@ -0,0 +1,15 @@
+// edition:2018
+// run-pass
+
+#![feature(async_await)]
+
+async fn lotsa_lifetimes<'a, 'b, 'c>(a: &'a u32, b: &'b u32, c: &'c u32) -> (&'a u32, &'b u32)
+    where 'b: 'a
+{
+    drop((a, c));
+    (b, b)
+}
+
+fn main() {
+    let _ = lotsa_lifetimes(&22, &44, &66);
+}

src/test/ui/async-await/multiple-lifetimes/ret-impl-trait-fg.rs

@@ -0,0 +1,18 @@
+// edition:2018
+// run-pass
+
+// Test that a feature gate is needed to use `impl Trait` as the
+// return type of an async.
+
+#![feature(async_await, member_constraints)]
+
+trait Trait<'a, 'b> { }
+impl<T> Trait<'_, '_> for T { }
+
+async fn async_ret_impl_trait<'a, 'b>(a: &'a u8, b: &'b u8) -> impl Trait<'a, 'b> {
+    (a, b)
+}
+
+fn main() {
+    let _ = async_ret_impl_trait(&22, &44);
+}

src/test/ui/async-await/multiple-lifetimes/ret-impl-trait-no-fg.rs

@@ -0,0 +1,18 @@
+// edition:2018
+
+// Test that a feature gate is needed to use `impl Trait` as the
+// return type of an async.
+
+#![feature(arbitrary_self_types, async_await, await_macro)]
+
+trait Trait<'a, 'b> { }
+impl<T> Trait<'_, '_> for T { }
+
+async fn async_ret_impl_trait<'a, 'b>(a: &'a u8, b: &'b u8) -> impl Trait<'a, 'b> {
+    //~^ ERROR ambiguous lifetime bound
+    (a, b)
+}
+
+fn main() {
+    let _ = async_ret_impl_trait(&22, &44);
+}

src/test/ui/async-await/multiple-lifetimes/ret-impl-trait-no-fg.stderr

@@ -0,0 +1,10 @@
+error: ambiguous lifetime bound in `impl Trait`
+  --> $DIR/ret-impl-trait-no-fg.rs:11:64
+   |
+LL | async fn async_ret_impl_trait<'a, 'b>(a: &'a u8, b: &'b u8) -> impl Trait<'a, 'b> {
+   |                                                                ^^^^^^^^^^^^^^^^^^ neither `'a` nor `'b` outlives the other
+   |
+   = help: add #![feature(member_constraints)] to the crate attributes to enable
+
+error: aborting due to previous error
+

src/test/ui/async-await/multiple-lifetimes/ret-impl-trait-one.rs

@@ -0,0 +1,27 @@
+// edition:2018
+
+// Test that a feature gate is needed to use `impl Trait` as the
+// return type of an async.
+
+#![feature(async_await, member_constraints)]
+
+trait Trait<'a> { }
+impl<T> Trait<'_> for T { }
+
+// Only `'a` permitted in return type, not `'b`.
+async fn async_ret_impl_trait1<'a, 'b>(a: &'a u8, b: &'b u8) -> impl Trait<'a> {
+    //~^ ERROR lifetime mismatch
+    (a, b)
+}
+
+// As above, but `'b: 'a`, so return type ca be inferred to `(&'a u8,
+// &'a u8)`.
+async fn async_ret_impl_trait2<'a, 'b>(a: &'a u8, b: &'b u8) -> impl Trait<'a>
+where
+    'b: 'a,
+{
+    (a, b)
+}
+
+fn main() {
+}

src/test/ui/async-await/multiple-lifetimes/ret-impl-trait-one.stderr

@@ -0,0 +1,11 @@
+error[E0623]: lifetime mismatch
+  --> $DIR/ret-impl-trait-one.rs:12:65
+   |
+LL | async fn async_ret_impl_trait1<'a, 'b>(a: &'a u8, b: &'b u8) -> impl Trait<'a> {
+   |                                           ------                ^^^^^^^^^^^^^^
+   |                                           |                     |
+   |                                           |                     ...but data from `b` is returned here
+   |                                           this parameter and the return type are declared with different lifetimes...
+
+error: aborting due to previous error
+

src/test/ui/async-await/multiple-lifetimes/ret-ref.rs

@@ -0,0 +1,46 @@
+// edition:2018
+
+// Test that we get the expected borrow check errors when an async
+// function (which takes multiple lifetimes) only returns data from
+// one of them.
+
+#![feature(async_await)]
+
+async fn multiple_named_lifetimes<'a, 'b>(a: &'a u8, _: &'b u8) -> &'a u8 {
+    a
+}
+
+// Both are borrowed whilst the future is live.
+async fn future_live() {
+    let mut a = 22;
+    let mut b = 44;
+    let future = multiple_named_lifetimes(&a, &b);
+    a += 1; //~ ERROR cannot assign
+    b += 1; //~ ERROR cannot assign
+    let p = future.await;
+    drop(p);
+}
+
+// Just the return value is live after future is awaited.
+async fn just_return_live() {
+    let mut a = 22;
+    let mut b = 44;
+    let future = multiple_named_lifetimes(&a, &b);
+    let p = future.await;
+    a += 1; //~ ERROR cannot assign
+    b += 1;
+    drop(p);
+}
+
+// Once `p` is dead, both `a` and `b` are unborrowed.
+async fn after_both_dead() {
+    let mut a = 22;
+    let mut b = 44;
+    let future = multiple_named_lifetimes(&a, &b);
+    let p = future.await;
+    drop(p);
+    a += 1;
+    b += 1;
+}
+
+fn main() { }

src/test/ui/async-await/multiple-lifetimes/ret-ref.stderr

@@ -0,0 +1,37 @@
+error[E0506]: cannot assign to `a` because it is borrowed
+  --> $DIR/ret-ref.rs:18:5
+   |
+LL |     let future = multiple_named_lifetimes(&a, &b);
+   |                                           -- borrow of `a` occurs here
+LL |     a += 1;
+   |     ^^^^^^ assignment to borrowed `a` occurs here
+LL |     b += 1;
+LL |     let p = future.await;
+   |             ------ borrow later used here
+
+error[E0506]: cannot assign to `b` because it is borrowed
+  --> $DIR/ret-ref.rs:19:5
+   |
+LL |     let future = multiple_named_lifetimes(&a, &b);
+   |                                               -- borrow of `b` occurs here
+LL |     a += 1;
+LL |     b += 1;
+   |     ^^^^^^ assignment to borrowed `b` occurs here
+LL |     let p = future.await;
+   |             ------ borrow later used here
+
+error[E0506]: cannot assign to `a` because it is borrowed
+  --> $DIR/ret-ref.rs:30:5
+   |
+LL |     let future = multiple_named_lifetimes(&a, &b);
+   |                                           -- borrow of `a` occurs here
+LL |     let p = future.await;
+LL |     a += 1;
+   |     ^^^^^^ assignment to borrowed `a` occurs here
+LL |     b += 1;
+LL |     drop(p);
+   |          - borrow later used here
+
+error: aborting due to 3 previous errors
+
+For more information about this error, try `rustc --explain E0506`.

src/test/ui/async-await/multiple-lifetimes/variance.rs

@@ -0,0 +1,18 @@
+// edition:2018
+// run-pass
+
+// Test for async fn where the parameters have distinct lifetime
+// parameters that appear in all possible variances.
+
+#![feature(arbitrary_self_types, async_await, await_macro)]
+
+#[allow(dead_code)]
+async fn lotsa_lifetimes<'a, 'b, 'c>(_: fn(&'a u8), _: fn(&'b u8) -> &'b u8, _: fn() -> &'c u8) { }
+
+fn take_any(_: &u8) { }
+fn identify(x: &u8) -> &u8 { x }
+fn give_back() -> &'static u8 { &22 }
+
+fn main() {
+    let _ = lotsa_lifetimes(take_any, identify, give_back);
+}