Auto merge of rust-lang#127827 - compiler-errors:async-closure-closur…

…e-async, r=<try>

[EXPERIMENT] Rewrite closure-of-async to async-closure

to see what the fallout is, to gauge how forwards-compatible `async || {}` is w/ `|| async {}`.

uwuwuwu

compiler/rustc_ast/src/ast.rs

@@ -1214,6 +1214,30 @@ impl Expr {
         }
     }
 
+    pub fn peel_uwu(&self) -> &Expr {
+        let mut expr = self;
+        loop {
+            match &expr.kind {
+                ExprKind::Block(blk, None) => {
+                    if blk.stmts.len() == 1
+                        && let StmtKind::Expr(blk) = &blk.stmts[0].kind
+                    {
+                        expr = blk;
+                    } else {
+                        break;
+                    }
+                }
+                ExprKind::Paren(paren) => {
+                    expr = paren;
+                }
+                _ => {
+                    break;
+                }
+            }
+        }
+        expr
+    }
+
     pub fn peel_parens(&self) -> &Expr {
         let mut expr = self;
         while let ExprKind::Paren(inner) = &expr.kind {
@@ -1614,15 +1638,16 @@ pub struct QSelf {
 }
 
 /// A capture clause used in closures and `async` blocks.
-#[derive(Clone, Copy, PartialEq, Encodable, Decodable, Debug, HashStable_Generic)]
+#[derive(Clone, Copy, PartialEq, Ord, Eq, PartialOrd, Debug)]
+#[derive(Encodable, Decodable, HashStable_Generic)]
 pub enum CaptureBy {
+    /// `move` keyword was not specified.
+    Ref,
     /// `move |x| y + x`.
     Value {
         /// The span of the `move` keyword.
         move_kw: Span,
     },
-    /// `move` keyword was not specified.
-    Ref,
 }
 
 /// Closure lifetime binder, `for<'a, 'b>` in `for<'a, 'b> |_: &'a (), _: &'b ()|`.

compiler/rustc_ast_lowering/src/expr.rs

@@ -218,18 +218,65 @@ impl<'hir> LoweringContext<'_, 'hir> {
                         *fn_decl_span,
                         *fn_arg_span,
                     ),
-                    None => self.lower_expr_closure(
-                        binder,
-                        *capture_clause,
-                        e.id,
-                        hir_id,
-                        *constness,
-                        *movability,
-                        fn_decl,
-                        body,
-                        *fn_decl_span,
-                        *fn_arg_span,
-                    ),
+                    None => {
+                        let peeled = body.peel_uwu();
+                        if let ast::ExprKind::Gen(
+                            gen_capture_clause,
+                            block,
+                            gen_kind @ ast::GenBlockKind::Async,
+                            span,
+                        ) = &peeled.kind
+                        {
+                            let coroutine_kind = match gen_kind {
+                                GenBlockKind::Async => CoroutineKind::Async {
+                                    span: *span,
+                                    closure_id: peeled.node_id(),
+                                    return_impl_trait_id: self.next_node_id(),
+                                },
+                                GenBlockKind::Gen => CoroutineKind::Gen {
+                                    span: *span,
+                                    closure_id: peeled.node_id(),
+                                    return_impl_trait_id: self.next_node_id(),
+                                },
+                                GenBlockKind::AsyncGen => CoroutineKind::AsyncGen {
+                                    span: *span,
+                                    closure_id: peeled.node_id(),
+                                    return_impl_trait_id: self.next_node_id(),
+                                },
+                            };
+                            let id = self.next_node_id();
+                            self.lower_expr_coroutine_closure(
+                                binder,
+                                (*capture_clause).max(*gen_capture_clause),
+                                e.id,
+                                hir_id,
+                                coroutine_kind,
+                                fn_decl,
+                                &ast::Expr {
+                                    id,
+                                    span: *span,
+                                    kind: ExprKind::Block(block.clone(), None),
+                                    attrs: thin_vec![],
+                                    tokens: None,
+                                },
+                                *fn_decl_span,
+                                *fn_arg_span,
+                            )
+                        } else {
+                            self.lower_expr_closure(
+                                binder,
+                                *capture_clause,
+                                e.id,
+                                hir_id,
+                                *constness,
+                                *movability,
+                                fn_decl,
+                                body,
+                                *fn_decl_span,
+                                *fn_arg_span,
+                            )
+                        }
+                    }
                 },
                 ExprKind::Gen(capture_clause, block, genblock_kind, decl_span) => {
                     let desugaring_kind = match genblock_kind {

compiler/rustc_mir_transform/src/shim.rs

@@ -434,6 +434,9 @@ fn build_clone_shim<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId, self_ty: Ty<'tcx>) -
     match self_ty.kind() {
         ty::FnDef(..) | ty::FnPtr(_) => builder.copy_shim(),
         ty::Closure(_, args) => builder.tuple_like_shim(dest, src, args.as_closure().upvar_tys()),
+        ty::CoroutineClosure(_, args) => {
+            builder.tuple_like_shim(dest, src, args.as_coroutine_closure().upvar_tys())
+        }
         ty::Tuple(..) => builder.tuple_like_shim(dest, src, self_ty.tuple_fields()),
         ty::Coroutine(coroutine_def_id, args) => {
             assert_eq!(tcx.coroutine_movability(*coroutine_def_id), hir::Movability::Movable);

compiler/rustc_next_trait_solver/src/solve/assembly/structural_traits.rs

@@ -216,7 +216,10 @@ where
         // impl Copy/Clone for Closure where Self::TupledUpvars: Copy/Clone
         ty::Closure(_, args) => Ok(vec![ty::Binder::dummy(args.as_closure().tupled_upvars_ty())]),
 
-        ty::CoroutineClosure(..) => Err(NoSolution),
+        // impl Copy/Clone for CoroutineClosure where Self::TupledUpvars: Copy/Clone
+        ty::CoroutineClosure(_, args) => {
+            Ok(vec![ty::Binder::dummy(args.as_coroutine_closure().tupled_upvars_ty())])
+        }
 
         // only when `coroutine_clone` is enabled and the coroutine is movable
         // impl Copy/Clone for Coroutine where T: Copy/Clone forall T in (upvars, witnesses)

compiler/rustc_trait_selection/src/traits/select/mod.rs

@@ -2262,8 +2262,21 @@ impl<'tcx> SelectionContext<'_, 'tcx> {
                 }
             }
 
-            // FIXME(async_closures): These are never clone, for now.
-            ty::CoroutineClosure(_, _) => None,
+            ty::CoroutineClosure(_, args) => {
+                // (*) binder moved here
+                let ty = self.infcx.shallow_resolve(args.as_coroutine_closure().tupled_upvars_ty());
+                if let ty::Infer(ty::TyVar(_)) = ty.kind() {
+                    // Not yet resolved.
+                    Ambiguous
+                } else {
+                    Where(
+                        obligation
+                            .predicate
+                            .rebind(args.as_coroutine_closure().upvar_tys().to_vec()),
+                    )
+                }
+            }
+
             // `Copy` and `Clone` are automatically implemented for an anonymous adt
             // if all of its fields are `Copy` and `Clone`
             ty::Adt(adt, args) if adt.is_anonymous() => {

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;
+}

tests/ui/async-await/async-closures/clone-closure.run.stdout

@@ -0,0 +1,2 @@
+Hello, world
+Hello, world2

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
 

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);

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
    |
@@ -72,6 +56,11 @@ LL |     outlives::<'a>(call_once(c));
 LL |
 LL |     let c = async move || { println!("{}", *x.0); };
    |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ move out of `x` occurs here
+   |
+help: consider cloning the value if the performance cost is acceptable
+   |
+LL |     let c = async || { println!("{}", *x.0); }.clone();
+   |                                               ++++++++
 
 error[E0597]: `c` does not live long enough
   --> $DIR/without-precise-captures-we-are-powerless.rs:33:20
@@ -146,7 +135,7 @@ 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`.

tests/ui/async-await/async-closures/wrong-fn-kind.stderr

@@ -1,24 +1,3 @@
-error[E0525]: expected a closure that implements the `async Fn` trait, but this closure only implements `async FnOnce`
-  --> $DIR/wrong-fn-kind.rs:17:20
-   |
-LL |       needs_async_fn(move || async move {
-   |       -------------- -^^^^^^
-   |       |              |
-   |  _____|______________this closure implements `async FnOnce`, not `async Fn`
-   | |     |
-   | |     required by a bound introduced by this call
-LL | |
-LL | |         println!("{x}");
-   | |                    - closure is `async FnOnce` because it moves the variable `x` out of its environment
-LL | |     });
-   | |_____- the requirement to implement `async Fn` derives from here
-   |
-note: required by a bound in `needs_async_fn`
-  --> $DIR/wrong-fn-kind.rs:5:27
-   |
-LL | fn needs_async_fn(_: impl async Fn()) {}
-   |                           ^^^^^^^^^^ required by this bound in `needs_async_fn`
-
 error[E0596]: cannot borrow `x` as mutable, as it is a captured variable in a `Fn` closure
   --> $DIR/wrong-fn-kind.rs:9:20
    |
@@ -35,7 +14,6 @@ LL |
 LL |         x += 1;
    |         - mutable borrow occurs due to use of `x` in closure
 
-error: aborting due to 2 previous errors
+error: aborting due to 1 previous error
 
-Some errors have detailed explanations: E0525, E0596.
-For more information about an error, try `rustc --explain E0525`.
+For more information about this error, try `rustc --explain E0596`.

tests/ui/async-await/issue-69446-fnmut-capture.stderr

@@ -1,19 +1,16 @@
-error: captured variable cannot escape `FnMut` closure body
-  --> $DIR/issue-69446-fnmut-capture.rs:19:17
+error: async closure does not implement `FnMut` because it captures state from its environment
+  --> $DIR/issue-69446-fnmut-capture.rs:19:9
    |
-LL |       let mut x = Foo;
-   |           ----- variable defined here
-LL |       bar(move || async {
-   |  _______________-_^
-   | |               |
-   | |               inferred to be a `FnMut` closure
-LL | |         x.foo();
-   | |         - variable captured here
-LL | |     });
-   | |_____^ returns an `async` block that contains a reference to a captured variable, which then escapes the closure body
+LL |     bar(move || async {
+   |     --- ^^^^^^^
+   |     |
+   |     required by a bound introduced by this call
    |
-   = note: `FnMut` closures only have access to their captured variables while they are executing...
-   = note: ...therefore, they cannot allow references to captured variables to escape
+note: required by a bound in `bar`
+  --> $DIR/issue-69446-fnmut-capture.rs:12:25
+   |
+LL | async fn bar<T>(_: impl FnMut() -> T)
+   |                         ^^^^^^^^^^^^ required by this bound in `bar`
 
 error: aborting due to 1 previous error
 

tests/ui/async-await/issue-70935-complex-spans.stderr

@@ -13,6 +13,7 @@ note: required because it appears within the type `NotSync`
 LL | struct NotSync(PhantomData<*mut ()>);
    |        ^^^^^^^
    = note: required for `&NotSync` to implement `Send`
+   = note: required because it appears within the type `(&NotSync,)`
 note: required because it's used within this closure
   --> $DIR/issue-70935-complex-spans.rs:19:13
    |
@@ -46,6 +47,7 @@ note: required because it appears within the type `NotSync`
 LL | struct NotSync(PhantomData<*mut ()>);
    |        ^^^^^^^
    = note: required for `&NotSync` to implement `Send`
+   = note: required because it appears within the type `(&NotSync,)`
 note: required because it's used within this closure
   --> $DIR/issue-70935-complex-spans.rs:19:13
    |

tests/ui/impl-trait/opaque-cast-field-access-in-future.stderr

@@ -1,3 +1,9 @@
+error[E0282]: type annotations needed
+  --> $DIR/opaque-cast-field-access-in-future.rs:7:14
+   |
+LL |         &mut foo.bar;
+   |              ^^^ cannot infer type
+
 error[E0283]: type annotations needed
   --> $DIR/opaque-cast-field-access-in-future.rs:22:17
    |
@@ -6,6 +12,7 @@ LL | fn run() -> Foo<impl Future<Output = ()>> {
    |
    = note: cannot satisfy `_: Future`
 
-error: aborting due to 1 previous error
+error: aborting due to 2 previous errors
 
-For more information about this error, try `rustc --explain E0283`.
+Some errors have detailed explanations: E0282, E0283.
+For more information about an error, try `rustc --explain E0282`.