Remove AsyncFn* impls from gnerator closures

eholk · eholk · commit f3fceff17d7b · 2025-05-23T14:30:59.000-07:00
diff --git a/compiler/rustc_const_eval/src/check_consts/check.rs b/compiler/rustc_const_eval/src/check_consts/check.rs
@@ -591,7 +591,7 @@ impl<'tcx> Visitor<'tcx> for Checker<'_, 'tcx> {
                 if let AggregateKind::Coroutine(def_id, ..) = kind.as_ref()
                     && let Some(
                         coroutine_kind @ hir::CoroutineKind::Desugared(
-                            hir::CoroutineDesugaring::Async,
+                            hir::CoroutineDesugaring::Async | hir::CoroutineDesugaring::Gen,
                             _,
                         ),
                     ) = self.tcx.coroutine_kind(def_id)
diff --git a/compiler/rustc_hir_typeck/src/closure.rs b/compiler/rustc_hir_typeck/src/closure.rs
@@ -470,7 +470,12 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 
             if let Some(trait_def_id) = trait_def_id {
                 let found_kind = match closure_kind {
-                    hir::ClosureKind::Closure => self.tcx.fn_trait_kind_from_def_id(trait_def_id),
+                    hir::ClosureKind::Closure
+                    // FIXME(iter_macro): Someday we'll probably want iterator closures instead of
+                    // just using Fn* for iterators.
+                    | hir::ClosureKind::CoroutineClosure(hir::CoroutineDesugaring::Gen) => {
+                        self.tcx.fn_trait_kind_from_def_id(trait_def_id)
+                    }
                     hir::ClosureKind::CoroutineClosure(hir::CoroutineDesugaring::Async) => self
                         .tcx
                         .async_fn_trait_kind_from_def_id(trait_def_id)
diff --git a/compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs b/compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs
@@ -11,7 +11,7 @@ use std::ops::ControlFlow;
 use hir::LangItem;
 use hir::def_id::DefId;
 use rustc_data_structures::fx::{FxHashSet, FxIndexSet};
-use rustc_hir as hir;
+use rustc_hir::{self as hir, CoroutineDesugaring, CoroutineKind};
 use rustc_infer::traits::{Obligation, PolyTraitObligation, SelectionError};
 use rustc_middle::ty::fast_reject::DeepRejectCtxt;
 use rustc_middle::ty::{self, Ty, TypeVisitableExt, TypingMode, elaborate};
@@ -438,6 +438,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         }
     }
 
+    #[instrument(level = "debug", skip(self, candidates))]
     fn assemble_async_closure_candidates(
         &mut self,
         obligation: &PolyTraitObligation<'tcx>,
@@ -446,15 +447,30 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         let goal_kind =
             self.tcx().async_fn_trait_kind_from_def_id(obligation.predicate.def_id()).unwrap();
 
+        debug!("self_ty = {:?}", obligation.self_ty().skip_binder().kind());
         match *obligation.self_ty().skip_binder().kind() {
-            ty::CoroutineClosure(_, args) => {
+            ty::CoroutineClosure(def_id, args) => {
                 if let Some(closure_kind) =
                     args.as_coroutine_closure().kind_ty().to_opt_closure_kind()
                     && !closure_kind.extends(goal_kind)
                 {
                     return;
                 }
-                candidates.vec.push(AsyncClosureCandidate);
+
+                // Make sure this is actually an async closure.
+                let Some(coroutine_kind) =
+                    self.tcx().coroutine_kind(self.tcx().coroutine_for_closure(def_id))
+                else {
+                    bug!("coroutine with no kind");
+                };
+
+                debug!(?coroutine_kind);
+                match coroutine_kind {
+                    CoroutineKind::Desugared(CoroutineDesugaring::Async, _) => {
+                        candidates.vec.push(AsyncClosureCandidate);
+                    }
+                    _ => (),
+                }
             }
             // Closures and fn pointers implement `AsyncFn*` if their return types
             // implement `Future`, which is checked later.
diff --git a/tests/ui/iterators/generator_capture_.rs b/tests/ui/iterators/generator_capture_.rs
@@ -1,4 +1,4 @@
-//@ run-pass
+// This test exercises lending behavior for iterator closures which is not yet supported.
 
 #![feature(iter_macro, yield_expr)]
 
@@ -18,7 +18,7 @@ fn main() {
     assert_eq!(i.next(), Some('o'));
     assert_eq!(i.next(), Some('o'));
     assert_eq!(i.next(), None);
-    let mut i = f();
+    let mut i = f(); //~ ERROR use of moved value: `f`
     assert_eq!(i.next(), Some('f'));
     assert_eq!(i.next(), Some('o'));
     assert_eq!(i.next(), Some('o'));
diff --git a/tests/ui/iterators/generator_capture_.stderr b/tests/ui/iterators/generator_capture_.stderr
@@ -0,0 +1,25 @@
+error[E0382]: use of moved value: `f`
+  --> $DIR/generator_capture_.rs:21:17
+   |
+LL |     let f = {
+   |         - move occurs because `f` has type `{gen closure@$DIR/generator_capture_.rs:10:17: 10:24}`, which does not implement the `Copy` trait
+...
+LL |     let mut i = f();
+   |                 --- `f` moved due to this call
+...
+LL |     let mut i = f();
+   |                 ^ value used here after move
+   |
+note: this value implements `FnOnce`, which causes it to be moved when called
+  --> $DIR/generator_capture_.rs:16:17
+   |
+LL |     let mut i = f();
+   |                 ^
+help: consider cloning the value if the performance cost is acceptable
+   |
+LL |     let mut i = f.clone()();
+   |                  ++++++++
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0382`.
diff --git a/tests/ui/iterators/generator_capture_fnonce.rs b/tests/ui/iterators/generator_capture_fnonce.rs
@@ -0,0 +1,32 @@
+//@ run-pass
+
+#![feature(iter_macro, yield_expr)]
+
+use std::iter::iter;
+
+fn main() {
+    let i = {
+        let s = String::new();
+        iter! { move || {
+            yield s.len();
+            for x in 5..10 {
+                yield x * 2;
+            }
+        }}
+    };
+    test_iterator(i);
+}
+
+/// Exercise the iterator in a separate function to ensure it's not capturing anything it shoudln't.
+fn test_iterator<I: Iterator<Item = usize>>(i: impl FnOnce() -> I) {
+    let mut i = i();
+    assert_eq!(i.next(), Some(0));
+    assert_eq!(i.next(), Some(10));
+    assert_eq!(i.next(), Some(12));
+    assert_eq!(i.next(), Some(14));
+    assert_eq!(i.next(), Some(16));
+    assert_eq!(i.next(), Some(18));
+    assert_eq!(i.next(), None);
+    assert_eq!(i.next(), None);
+    assert_eq!(i.next(), None);
+}
diff --git a/tests/ui/iterators/iter-macro-not-async-closure.rs b/tests/ui/iterators/iter-macro-not-async-closure.rs
@@ -23,6 +23,7 @@ fn main() {
     //~^ ERROR AsyncFnOnce()` is not satisfied
     //~^^ ERROR AsyncFnOnce()` is not satisfied
     //~^^^ ERROR AsyncFnOnce()` is not satisfied
+    //~^^^^ ERROR AsyncFnOnce()` is not satisfied
     x.poll(&mut Context::from_waker(Waker::noop()));
     //~^ ERROR AsyncFnOnce()` is not satisfied
 }
diff --git a/tests/ui/iterators/iter-macro-not-async-closure.stderr b/tests/ui/iterators/iter-macro-not-async-closure.stderr
@@ -41,7 +41,21 @@ LL | async fn call_async_once(f: impl AsyncFnOnce()) {
    = note: this error originates in the macro `pin` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error[E0277]: the trait bound `{gen closure@$DIR/iter-macro-not-async-closure.rs:16:21: 16:28}: AsyncFnOnce()` is not satisfied
-  --> $DIR/iter-macro-not-async-closure.rs:26:5
+  --> $DIR/iter-macro-not-async-closure.rs:22:13
+   |
+LL |     let x = pin!(call_async_once(f));
+   |             ^^^^^^^^^^^^^^^^^^^^^^^^ unsatisfied trait bound
+   |
+   = help: the trait `AsyncFnOnce()` is not implemented for `{gen closure@$DIR/iter-macro-not-async-closure.rs:16:21: 16:28}`
+note: required by a bound in `call_async_once`
+  --> $DIR/iter-macro-not-async-closure.rs:11:34
+   |
+LL | async fn call_async_once(f: impl AsyncFnOnce()) {
+   |                                  ^^^^^^^^^^^^^ required by this bound in `call_async_once`
+   = note: this error originates in the macro `pin` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the trait bound `{gen closure@$DIR/iter-macro-not-async-closure.rs:16:21: 16:28}: AsyncFnOnce()` is not satisfied
+  --> $DIR/iter-macro-not-async-closure.rs:27:5
    |
 LL |     x.poll(&mut Context::from_waker(Waker::noop()));
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ unsatisfied trait bound
@@ -53,6 +67,6 @@ note: required by a bound in `call_async_once`
 LL | async fn call_async_once(f: impl AsyncFnOnce()) {
    |                                  ^^^^^^^^^^^^^ required by this bound in `call_async_once`
 
-error: aborting due to 4 previous errors
+error: aborting due to 5 previous errors
 
 For more information about this error, try `rustc --explain E0277`.

Original file line number	Diff line number	Diff line change
`@@ -23,6 +23,7 @@ fn main() {`
`23`	`23`	//~^ ERROR AsyncFnOnce()` is not satisfied
`24`	`24`	//~^^ ERROR AsyncFnOnce()` is not satisfied
`25`	`25`	//~^^^ ERROR AsyncFnOnce()` is not satisfied
	`26`	+ //~^^^^ ERROR AsyncFnOnce()` is not satisfied
`26`	`27`	`x.poll(&mut Context::from_waker(Waker::noop()));`
`27`	`28`	//~^ ERROR AsyncFnOnce()` is not satisfied
`28`	`29`	`}`