Autoref/deref for .await

Author: Jules-Bertholet

compiler/rustc_ast_lowering/src/expr.rs

@@ -730,7 +730,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
 
     /// Desugar `<expr>.await` into:
     /// ```ignore (pseudo-rust)
-    /// match ::std::future::IntoFuture::into_future(<expr>) {
+    /// match (<expr>).<::std::future::IntoFuture::into_future>() {
     ///     mut __awaitee => loop {
     ///         match unsafe { ::std::future::Future::poll(
     ///             <::std::pin::Pin>::new_unchecked(&mut __awaitee),
@@ -930,13 +930,33 @@ impl<'hir> LoweringContext<'_, 'hir> {
         // mut __awaitee => loop { ... }
         let awaitee_arm = self.arm(awaitee_pat, loop_expr);
 
-        // `match ::std::future::IntoFuture::into_future(<expr>) { ... }`
         let into_future_expr = match await_kind {
-            FutureKind::Future => self.expr_call_lang_item_fn(
-                span,
-                hir::LangItem::IntoFutureIntoFuture,
-                arena_vec![self; *expr],
-            ),
+            // `match (<expr>).<::std::future::IntoFuture::into_future>() { ... }`
+            // The `into_future` call is a little special,
+            // it resolves directly to the `into_future` lang item
+            // but goes through autoref/autoderef like any method call.
+            FutureKind::Future => {
+                let into_future_id = self
+                    .tcx
+                    .require_lang_item(hir::LangItem::IntoFutureIntoFuture, Some(await_kw_span));
+
+                let segment_hid = self.next_id();
+
+                self.arena.alloc(self.expr(
+                    span,
+                    hir::ExprKind::MethodCall(
+                        self.arena.alloc(hir::PathSegment::new(
+                            Ident::new(sym::into_future, await_kw_span),
+                            segment_hid,
+                            Res::Def(DefKind::AssocFn, into_future_id),
+                        )),
+                        self.arena.alloc(expr),
+                        &[],
+                        span,
+                    ),
+                ))
+            }
+
             // Not needed for `for await` because we expect to have already called
             // `IntoAsyncIterator::into_async_iter` on it.
             FutureKind::AsyncIterator => expr,

compiler/rustc_hir_typeck/src/method/mod.rs

@@ -182,8 +182,9 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         self_expr: &'tcx hir::Expr<'tcx>,
         args: &'tcx [hir::Expr<'tcx>],
     ) -> Result<MethodCallee<'tcx>, MethodError<'tcx>> {
-        let pick =
-            self.lookup_probe(segment.ident, self_ty, call_expr, ProbeScope::TraitsInScope)?;
+        let probe_scope =
+            segment.res.opt_def_id().map_or(ProbeScope::TraitsInScope, ProbeScope::DefId);
+        let pick = self.lookup_probe(segment.ident, self_ty, call_expr, probe_scope)?;
 
         self.lint_dot_call_from_2018(self_ty, segment, span, call_expr, self_expr, &pick, args);
 
@@ -202,12 +203,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             if let ty::Ref(region, t_type, mutability) = self_ty.kind() {
                 let trait_type = Ty::new_ref(self.tcx, *region, *t_type, mutability.invert());
                 // We probe again to see if there might be a borrow mutability discrepancy.
-                match self.lookup_probe(
-                    segment.ident,
-                    trait_type,
-                    call_expr,
-                    ProbeScope::TraitsInScope,
-                ) {
+                match self.lookup_probe(segment.ident, trait_type, call_expr, probe_scope) {
                     Ok(ref new_pick) if pick.differs_from(new_pick) => {
                         needs_mut = new_pick.self_ty.ref_mutability() != self_ty.ref_mutability();
                     }
@@ -216,29 +212,33 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             }
 
             // We probe again, taking all traits into account (not only those in scope).
-            let candidates = match self.lookup_probe_for_diagnostic(
-                segment.ident,
-                self_ty,
-                call_expr,
-                ProbeScope::AllTraits,
-                None,
-            ) {
-                // If we find a different result the caller probably forgot to import a trait.
-                Ok(ref new_pick) if pick.differs_from(new_pick) => {
-                    vec![new_pick.item.container_id(self.tcx)]
+            let candidates = if probe_scope == ProbeScope::TraitsInScope {
+                match self.lookup_probe_for_diagnostic(
+                    segment.ident,
+                    self_ty,
+                    call_expr,
+                    ProbeScope::AllTraits,
+                    None,
+                ) {
+                    // If we find a different result the caller probably forgot to import a trait.
+                    Ok(ref new_pick) if pick.differs_from(new_pick) => {
+                        vec![new_pick.item.container_id(self.tcx)]
+                    }
+                    Err(Ambiguity(ref sources)) => sources
+                        .iter()
+                        .filter_map(|source| {
+                            match *source {
+                                // Note: this cannot come from an inherent impl,
+                                // because the first probing succeeded.
+                                CandidateSource::Impl(def) => self.tcx.trait_id_of_impl(def),
+                                CandidateSource::Trait(_) => None,
+                            }
+                        })
+                        .collect(),
+                    _ => Vec::new(),
                 }
-                Err(Ambiguity(ref sources)) => sources
-                    .iter()
-                    .filter_map(|source| {
-                        match *source {
-                            // Note: this cannot come from an inherent impl,
-                            // because the first probing succeeded.
-                            CandidateSource::Impl(def) => self.tcx.trait_id_of_impl(def),
-                            CandidateSource::Trait(_) => None,
-                        }
-                    })
-                    .collect(),
-                _ => Vec::new(),
+            } else {
+                Vec::new()
             };
 
             return Err(IllegalSizedBound { candidates, needs_mut, bound_span: span, self_expr });
@@ -255,13 +255,11 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         call_expr: &'tcx hir::Expr<'tcx>,
         self_expr: &'tcx hir::Expr<'tcx>,
     ) -> Result<MethodCallee<'tcx>, MethodError<'tcx>> {
-        let pick = self.lookup_probe_for_diagnostic(
-            segment.ident,
-            self_ty,
-            call_expr,
-            ProbeScope::TraitsInScope,
-            None,
-        )?;
+        let probe_scope =
+            segment.res.opt_def_id().map_or(ProbeScope::TraitsInScope, ProbeScope::DefId);
+
+        let pick =
+            self.lookup_probe_for_diagnostic(segment.ident, self_ty, call_expr, probe_scope, None)?;
 
         Ok(self
             .confirm_method_for_diagnostic(span, self_expr, call_expr, self_ty, &pick, segment)

compiler/rustc_hir_typeck/src/method/probe.rs

@@ -248,6 +248,9 @@ pub enum ProbeScope {
 
     // Assemble candidates coming from all traits.
     AllTraits,
+
+    // Consider only the given `DefId`.
+    DefId(DefId),
 }
 
 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
@@ -495,6 +498,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     probe_cx.assemble_extension_candidates_for_traits_in_scope()
                 }
                 ProbeScope::AllTraits => probe_cx.assemble_extension_candidates_for_all_traits(),
+                ProbeScope::DefId(id) => probe_cx.assemble_extension_candidate_for_def_id(id),
             };
             op(probe_cx)
         })
@@ -919,6 +923,26 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
         }
     }
 
+    fn assemble_extension_candidate_for_def_id(&mut self, fn_id: DefId) {
+        let item: AssocItem = self.tcx.associated_item(fn_id);
+        let trait_def_id = item.trait_container(self.tcx).expect("method should have a trait");
+        let trait_args = self.fresh_args_for_item(self.span, trait_def_id);
+        let trait_ref = ty::TraitRef::new(self.tcx, trait_def_id, trait_args);
+        let (xform_self_ty, xform_ret_ty) =
+            self.xform_self_ty(item, trait_ref.self_ty(), trait_args);
+
+        self.push_candidate(
+            Candidate {
+                xform_self_ty,
+                xform_ret_ty,
+                item,
+                import_ids: smallvec![],
+                kind: TraitCandidate(trait_ref),
+            },
+            false,
+        );
+    }
+
     fn matches_return_type(
         &self,
         method: ty::AssocItem,

tests/ui/async-await/await-into-future-autoref.rs

@@ -0,0 +1,44 @@
+// run-pass
+// aux-build: issue-72470-lib.rs
+// edition:2021
+extern crate issue_72470_lib;
+use std::{future::{Future, IntoFuture}, pin::Pin};
+
+struct AwaitMe;
+
+impl IntoFuture for &AwaitMe {
+    type Output = i32;
+    type IntoFuture = Pin<Box<dyn Future<Output = i32>>>;
+
+    fn into_future(self) -> Self::IntoFuture {
+        Box::pin(me())
+    }
+}
+
+async fn me() -> i32 {
+    41
+}
+
+async fn run() {
+    assert_eq!(AwaitMe.await, 41);
+}
+
+struct AwaitMeToo;
+
+impl IntoFuture for &mut AwaitMeToo {
+    type Output = i32;
+    type IntoFuture = Pin<Box<dyn Future<Output = i32>>>;
+
+    fn into_future(self) -> Self::IntoFuture {
+        Box::pin(me())
+    }
+}
+
+async fn run_too() {
+    assert_eq!(AwaitMeToo.await, 41);
+}
+
+fn main() {
+    issue_72470_lib::run(run());
+    issue_72470_lib::run(run_too());
+}