Rollup merge of #128201 - compiler-errors:closure-clone, r=oli-obk

Implement `Copy`/`Clone` for async closures

We can do so in the same cases that regular closures do.

For the purposes of cloning, coroutine-closures are actually precisely the same as regular closures, specifically in the aspect that `Clone` impls care about which is the upvars. The only difference b/w coroutine-closures and regular closures is the type that they *return*, but this type has not been *created* yet, so we don't really have a problem.

IDK why I didn't add this impl initially -- I went back and forth a bit on the internal representation for coroutine-closures before settling on a design which largely models regular closures. Previous (not published) iterations of coroutine-closures used to be represented as a special (read: cursed) kind of coroutine, which would probably suffer from the pitfalls that coroutines have that oli mentioned below in https://github.com/rust-lang/rust/pull/128201#issuecomment-2251230274.

r? oli-obk

7 files changed, 93 insertions, 18 deletions

diff --git a/tests/ui/async-await/async-closures/clone-closure.rs b/tests/ui/async-await/async-closures/clone-closure.rs
new file mode 100644
index 00000000000..807897e3e03
--- /dev/null
+++ b/tests/ui/async-await/async-closures/clone-closure.rs
@@ -0,0 +1,24 @@
+//@ aux-build:block-on.rs
+//@ edition:2021
+//@ run-pass
+//@ check-run-results
+
+#![feature(async_closure)]
+
+extern crate block_on;
+
+async fn for_each(f: impl async FnOnce(&str) + Clone) {
+    f.clone()("world").await;
+    f.clone()("world2").await;
+}
+
+fn main() {
+    block_on::block_on(async_main());
+}
+
+async fn async_main() {
+    let x = String::from("Hello,");
+    for_each(async move |s| {
+        println!("{x} {s}");
+    }).await;
+}
diff --git a/tests/ui/async-await/async-closures/clone-closure.run.stdout b/tests/ui/async-await/async-closures/clone-closure.run.stdout
new file mode 100644
index 00000000000..0cfcf1923da
--- /dev/null
+++ b/tests/ui/async-await/async-closures/clone-closure.run.stdout
@@ -0,0 +1,2 @@
+Hello, world
+Hello, world2
diff --git a/tests/ui/async-await/async-closures/move-consuming-capture.stderr b/tests/ui/async-await/async-closures/move-consuming-capture.stderr
index 45c1eac8f8f..4ce71ec49d6 100644
--- a/tests/ui/async-await/async-closures/move-consuming-capture.stderr
+++ b/tests/ui/async-await/async-closures/move-consuming-capture.stderr
@@ -11,6 +11,15 @@ LL |         x().await;
    |
 note: `async_call_once` takes ownership of the receiver `self`, which moves `x`
   --> $SRC_DIR/core/src/ops/async_function.rs:LL:COL
+help: you could `clone` the value and consume it, if the `NoCopy: Clone` trait bound could be satisfied
+   |
+LL |         x.clone()().await;
+   |          ++++++++
+help: consider annotating `NoCopy` with `#[derive(Clone)]`
+   |
+LL + #[derive(Clone)]
+LL | struct NoCopy;
+   |
 
 error: aborting due to 1 previous error
 
diff --git a/tests/ui/async-await/async-closures/not-clone-closure.rs b/tests/ui/async-await/async-closures/not-clone-closure.rs
new file mode 100644
index 00000000000..2776ce4690f
--- /dev/null
+++ b/tests/ui/async-await/async-closures/not-clone-closure.rs
@@ -0,0 +1,36 @@
+//@ edition: 2021
+
+#![feature(async_closure)]
+
+struct NotClonableArg;
+#[derive(Default)]
+struct NotClonableReturnType;
+
+// Verify that the only components that we care about are the upvars, not the signature.
+fn we_are_okay_with_not_clonable_signature() {
+    let x = async |x: NotClonableArg| -> NotClonableReturnType { Default::default() };
+    x.clone(); // Okay
+}
+
+#[derive(Debug)]
+struct NotClonableUpvar;
+
+fn we_only_care_about_clonable_upvars() {
+    let x = NotClonableUpvar;
+    // Notably, this is clone because we capture `&x`.
+    let yes_clone = async || {
+        println!("{x:?}");
+    };
+    yes_clone.clone(); // Okay
+
+    let z = NotClonableUpvar;
+    // However, this is not because the closure captures `z` by move.
+    // (Even though the future that is lent out captures `z by ref!)
+    let not_clone = async move || {
+        println!("{z:?}");
+    };
+    not_clone.clone();
+    //~^ ERROR the trait bound `NotClonableUpvar: Clone` is not satisfied
+}
+
+fn main() {}
diff --git a/tests/ui/async-await/async-closures/not-clone-closure.stderr b/tests/ui/async-await/async-closures/not-clone-closure.stderr
new file mode 100644
index 00000000000..aea48a455c2
--- /dev/null
+++ b/tests/ui/async-await/async-closures/not-clone-closure.stderr
@@ -0,0 +1,20 @@
+error[E0277]: the trait bound `NotClonableUpvar: Clone` is not satisfied in `{async closure@$DIR/not-clone-closure.rs:29:21: 29:34}`
+  --> $DIR/not-clone-closure.rs:32:15
+   |
+LL |     not_clone.clone();
+   |               ^^^^^ within `{async closure@$DIR/not-clone-closure.rs:29:21: 29:34}`, the trait `Clone` is not implemented for `NotClonableUpvar`, which is required by `{async closure@$DIR/not-clone-closure.rs:29:21: 29:34}: Clone`
+   |
+note: required because it's used within this closure
+  --> $DIR/not-clone-closure.rs:29:21
+   |
+LL |     let not_clone = async move || {
+   |                     ^^^^^^^^^^^^^
+help: consider annotating `NotClonableUpvar` with `#[derive(Clone)]`
+   |
+LL + #[derive(Clone)]
+LL | struct NotClonableUpvar;
+   |
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0277`.
diff --git a/tests/ui/async-await/async-closures/without-precise-captures-we-are-powerless.rs b/tests/ui/async-await/async-closures/without-precise-captures-we-are-powerless.rs
index 17681161e20..18f16ca4b2d 100644
--- a/tests/ui/async-await/async-closures/without-precise-captures-we-are-powerless.rs
+++ b/tests/ui/async-await/async-closures/without-precise-captures-we-are-powerless.rs
@@ -19,7 +19,7 @@ fn simple<'a>(x: &'a i32) {
 
     let c = async move || { println!("{}", *x); };
     outlives::<'a>(c()); //~ ERROR `c` does not live long enough
-    outlives::<'a>(call_once(c)); //~ ERROR cannot move out of `c`
+    outlives::<'a>(call_once(c));
 }
 
 struct S<'a>(&'a i32);
diff --git a/tests/ui/async-await/async-closures/without-precise-captures-we-are-powerless.stderr b/tests/ui/async-await/async-closures/without-precise-captures-we-are-powerless.stderr
index 569028934cb..1df5abdbb18 100644
--- a/tests/ui/async-await/async-closures/without-precise-captures-we-are-powerless.stderr
+++ b/tests/ui/async-await/async-closures/without-precise-captures-we-are-powerless.stderr
@@ -29,22 +29,6 @@ LL |     outlives::<'a>(call_once(c));
 LL | }
    | - `c` dropped here while still borrowed
 
-error[E0505]: cannot move out of `c` because it is borrowed
-  --> $DIR/without-precise-captures-we-are-powerless.rs:22:30
-   |
-LL | fn simple<'a>(x: &'a i32) {
-   |           -- lifetime `'a` defined here
-...
-LL |     let c = async move || { println!("{}", *x); };
-   |         - binding `c` declared here
-LL |     outlives::<'a>(c());
-   |                    ---
-   |                    |
-   |                    borrow of `c` occurs here
-   |                    argument requires that `c` is borrowed for `'a`
-LL |     outlives::<'a>(call_once(c));
-   |                              ^ move out of `c` occurs here
-
 error[E0597]: `x` does not live long enough
   --> $DIR/without-precise-captures-we-are-powerless.rs:28:13
    |
@@ -146,7 +130,7 @@ LL |     // outlives::<'a>(call_once(c)); // FIXME(async_closures): Figure out w
 LL | }
    | - `c` dropped here while still borrowed
 
-error: aborting due to 10 previous errors
+error: aborting due to 9 previous errors
 
 Some errors have detailed explanations: E0505, E0597, E0621.
 For more information about an error, try `rustc --explain E0505`.