[beta] backport

compiler/rustc_lint/src/unused.rs

@@ -103,8 +103,10 @@ impl<'tcx> LateLintPass<'tcx> for UnusedResults {
             && let ty = cx.typeck_results().expr_ty(&await_expr)
             && let ty::Alias(ty::Opaque, ty::AliasTy { def_id: future_def_id, .. }) = ty.kind()
             && cx.tcx.ty_is_opaque_future(ty)
-            // FIXME: This also includes non-async fns that return `impl Future`.
             && let async_fn_def_id = cx.tcx.parent(*future_def_id)
+            && matches!(cx.tcx.def_kind(async_fn_def_id), DefKind::Fn | DefKind::AssocFn)
+            // Check that this `impl Future` actually comes from an `async fn`
+            && cx.tcx.asyncness(async_fn_def_id).is_async()
             && check_must_use_def(
                 cx,
                 async_fn_def_id,

compiler/rustc_middle/src/traits/mod.rs

@@ -697,9 +697,9 @@ impl<'tcx, N> ImplSource<'tcx, N> {
     }
 
     pub fn borrow_nested_obligations(&self) -> &[N] {
-        match &self {
-            ImplSource::UserDefined(i) => &i.nested[..],
-            ImplSource::Param(n, _) => &n,
+        match self {
+            ImplSource::UserDefined(i) => &i.nested,
+            ImplSource::Param(n, _) => n,
             ImplSource::Builtin(i) => &i.nested,
             ImplSource::AutoImpl(d) => &d.nested,
             ImplSource::Closure(c) => &c.nested,
@@ -713,6 +713,23 @@ impl<'tcx, N> ImplSource<'tcx, N> {
         }
     }
 
+    pub fn borrow_nested_obligations_mut(&mut self) -> &mut [N] {
+        match self {
+            ImplSource::UserDefined(i) => &mut i.nested,
+            ImplSource::Param(n, _) => n,
+            ImplSource::Builtin(i) => &mut i.nested,
+            ImplSource::AutoImpl(d) => &mut d.nested,
+            ImplSource::Closure(c) => &mut c.nested,
+            ImplSource::Generator(c) => &mut c.nested,
+            ImplSource::Future(c) => &mut c.nested,
+            ImplSource::Object(d) => &mut d.nested,
+            ImplSource::FnPointer(d) => &mut d.nested,
+            ImplSource::TraitAlias(d) => &mut d.nested,
+            ImplSource::TraitUpcasting(d) => &mut d.nested,
+            ImplSource::ConstDestruct(i) => &mut i.nested,
+        }
+    }
+
     pub fn map<M, F>(self, f: F) -> ImplSource<'tcx, M>
     where
         F: FnMut(N) -> M,

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

@@ -131,6 +131,12 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             }
         };
 
+        // The obligations returned by confirmation are recursively evaluated
+        // so we need to make sure they have the correct depth.
+        for subobligation in impl_src.borrow_nested_obligations_mut() {
+            subobligation.set_depth_from_parent(obligation.recursion_depth);
+        }
+
         if !obligation.predicate.is_const_if_const() {
             // normalize nested predicates according to parent predicate's constness.
             impl_src = impl_src.map(|mut o| {

tests/ui/lint/unused/auxiliary/must-use-foreign.rs

@@ -0,0 +1,12 @@
+// edition:2021
+
+use std::future::Future;
+
+pub struct Manager;
+
+impl Manager {
+    #[must_use]
+    pub async fn new() -> (Self, impl Future<Output = ()>) {
+        (Manager, async {})
+    }
+}

tests/ui/lint/unused/must-use-foreign.rs

@@ -0,0 +1,15 @@
+// edition:2021
+// aux-build:must-use-foreign.rs
+// check-pass
+
+extern crate must_use_foreign;
+
+use must_use_foreign::Manager;
+
+async fn async_main() {
+    Manager::new().await.1.await;
+}
+
+fn main() {
+    let _ = async_main();
+}

tests/ui/lint/unused/unused-async.rs

@@ -33,7 +33,7 @@ async fn test() {
     foo().await; //~ ERROR unused output of future returned by `foo` that must be used
     bar(); //~ ERROR unused return value of `bar` that must be used
     //~^ ERROR unused implementer of `Future` that must be used
-    bar().await; //~ ERROR unused output of future returned by `bar` that must be used
+    bar().await; // ok, it's not an async fn
     baz(); //~ ERROR unused implementer of `Future` that must be used
     baz().await; // ok
 }

tests/ui/lint/unused/unused-async.stderr

@@ -52,17 +52,6 @@ help: use `let _ = ...` to ignore the resulting value
 LL |     let _ = bar();
    |     +++++++
 
-error: unused output of future returned by `bar` that must be used
-  --> $DIR/unused-async.rs:36:5
-   |
-LL |     bar().await;
-   |     ^^^^^^^^^^^
-   |
-help: use `let _ = ...` to ignore the resulting value
-   |
-LL |     let _ = bar().await;
-   |     +++++++
-
 error: unused implementer of `Future` that must be used
   --> $DIR/unused-async.rs:37:5
    |
@@ -71,5 +60,5 @@ LL |     baz();
    |
    = note: futures do nothing unless you `.await` or poll them
 
-error: aborting due to 7 previous errors
+error: aborting due to 6 previous errors
 

tests/ui/traits/cycle-cache-err-60010.stderr

@@ -1,9 +1,22 @@
-error[E0275]: overflow evaluating the requirement `RootDatabase: RefUnwindSafe`
+error[E0275]: overflow evaluating the requirement `SalsaStorage: RefUnwindSafe`
   --> $DIR/cycle-cache-err-60010.rs:27:13
    |
 LL |     _parse: <ParseQuery as Query<RootDatabase>>::Data,
    |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
+   = note: required because it appears within the type `PhantomData<SalsaStorage>`
+   = note: required because it appears within the type `Unique<SalsaStorage>`
+   = note: required because it appears within the type `Box<SalsaStorage>`
+note: required because it appears within the type `Runtime<RootDatabase>`
+  --> $DIR/cycle-cache-err-60010.rs:23:8
+   |
+LL | struct Runtime<DB: Database> {
+   |        ^^^^^^^
+note: required because it appears within the type `RootDatabase`
+  --> $DIR/cycle-cache-err-60010.rs:20:8
+   |
+LL | struct RootDatabase {
+   |        ^^^^^^^^^^^^
 note: required for `RootDatabase` to implement `SourceDatabase`
   --> $DIR/cycle-cache-err-60010.rs:44:9
    |

tests/ui/traits/solver-cycles/cycle-via-builtin-auto-trait-impl.rs

@@ -0,0 +1,34 @@
+//~ ERROR overflow
+// A regression test for #111729 checking that we correctly
+// track recursion depth for obligations returned by confirmation.
+use std::panic::RefUnwindSafe;
+
+trait Database {
+    type Storage;
+}
+trait Query<DB> {
+    type Data;
+}
+struct ParseQuery;
+struct RootDatabase {
+    _runtime: Runtime<RootDatabase>,
+}
+
+impl<T: RefUnwindSafe> Database for T {
+    type Storage = SalsaStorage;
+}
+impl Database for RootDatabase {
+    type Storage = SalsaStorage;
+}
+
+struct Runtime<DB: Database> {
+    _storage: Box<DB::Storage>,
+}
+struct SalsaStorage {
+    _parse: <ParseQuery as Query<RootDatabase>>::Data,
+}
+
+impl<DB: Database> Query<DB> for ParseQuery {
+    type Data = RootDatabase;
+}
+fn main() {}

tests/ui/traits/solver-cycles/cycle-via-builtin-auto-trait-impl.stderr

@@ -0,0 +1,24 @@
+error[E0275]: overflow evaluating the requirement `Runtime<RootDatabase>: RefUnwindSafe`
+   |
+   = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`cycle_via_builtin_auto_trait_impl`)
+note: required because it appears within the type `RootDatabase`
+  --> $DIR/cycle-via-builtin-auto-trait-impl.rs:13:8
+   |
+LL | struct RootDatabase {
+   |        ^^^^^^^^^^^^
+note: required for `RootDatabase` to implement `Database`
+  --> $DIR/cycle-via-builtin-auto-trait-impl.rs:17:24
+   |
+LL | impl<T: RefUnwindSafe> Database for T {
+   |         -------------  ^^^^^^^^     ^
+   |         |
+   |         unsatisfied trait bound introduced here
+note: required because it appears within the type `Runtime<RootDatabase>`
+  --> $DIR/cycle-via-builtin-auto-trait-impl.rs:24:8
+   |
+LL | struct Runtime<DB: Database> {
+   |        ^^^^^^^
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0275`.