Rollup merge of #90939 - estebank:wg-af-polish, r=tmandry

Tweak errors coming from `for`-loop, `?` and `.await` desugaring

 * Suggest removal of `.await` on non-`Future` expression
 * Keep track of obligations introduced by desugaring
 * Remove span pointing at method for obligation errors coming from desugaring
 * Point at called local sync `fn` and suggest making it `async`

```
error[E0277]: `()` is not a future
  --> $DIR/unnecessary-await.rs:9:10
   |
LL |     boo().await;
   |     -----^^^^^^ `()` is not a future
   |     |
   |     this call returns `()`
   |
   = help: the trait `Future` is not implemented for `()`
help: do not `.await` the expression
   |
LL -     boo().await;
LL +     boo();
   |
help: alternatively, consider making `fn boo` asynchronous
   |
LL | async fn boo () {}
   | +++++
```

Fix #66731.

compiler/rustc_ast_lowering/src/expr.rs

@@ -130,7 +130,15 @@ impl<'hir> LoweringContext<'_, 'hir> {
                         hir::AsyncGeneratorKind::Block,
                         |this| this.with_new_scopes(|this| this.lower_block_expr(block)),
                     ),
-                ExprKind::Await(ref expr) => self.lower_expr_await(e.span, expr),
+                ExprKind::Await(ref expr) => {
+                    let span = if expr.span.hi() < e.span.hi() {
+                        expr.span.shrink_to_hi().with_hi(e.span.hi())
+                    } else {
+                        // this is a recovered `await expr`
+                        e.span
+                    };
+                    self.lower_expr_await(span, expr)
+                }
                 ExprKind::Closure(
                     capture_clause,
                     asyncness,
@@ -479,8 +487,12 @@ impl<'hir> LoweringContext<'_, 'hir> {
         expr: &'hir hir::Expr<'hir>,
         overall_span: Span,
     ) -> &'hir hir::Expr<'hir> {
-        let constructor =
-            self.arena.alloc(self.expr_lang_item_path(method_span, lang_item, ThinVec::new()));
+        let constructor = self.arena.alloc(self.expr_lang_item_path(
+            method_span,
+            lang_item,
+            ThinVec::new(),
+            None,
+        ));
         self.expr_call(overall_span, constructor, std::slice::from_ref(expr))
     }
 
@@ -584,8 +596,12 @@ impl<'hir> LoweringContext<'_, 'hir> {
         // `future::from_generator`:
         let unstable_span =
             self.mark_span_with_reason(DesugaringKind::Async, span, self.allow_gen_future.clone());
-        let gen_future =
-            self.expr_lang_item_path(unstable_span, hir::LangItem::FromGenerator, ThinVec::new());
+        let gen_future = self.expr_lang_item_path(
+            unstable_span,
+            hir::LangItem::FromGenerator,
+            ThinVec::new(),
+            None,
+        );
 
         // `future::from_generator(generator)`:
         hir::ExprKind::Call(self.arena.alloc(gen_future), arena_vec![self; generator])
@@ -607,6 +623,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
     /// }
     /// ```
     fn lower_expr_await(&mut self, await_span: Span, expr: &Expr) -> hir::ExprKind<'hir> {
+        let dot_await_span = expr.span.shrink_to_hi().to(await_span);
         match self.generator_kind {
             Some(hir::GeneratorKind::Async(_)) => {}
             Some(hir::GeneratorKind::Gen) | None => {
@@ -623,13 +640,14 @@ impl<'hir> LoweringContext<'_, 'hir> {
                 err.emit();
             }
         }
-        let span = self.mark_span_with_reason(DesugaringKind::Await, await_span, None);
+        let span = self.mark_span_with_reason(DesugaringKind::Await, dot_await_span, None);
         let gen_future_span = self.mark_span_with_reason(
             DesugaringKind::Await,
             await_span,
             self.allow_gen_future.clone(),
         );
         let expr = self.lower_expr_mut(expr);
+        let expr_hir_id = expr.hir_id;
 
         let pinned_ident = Ident::with_dummy_span(sym::pinned);
         let (pinned_pat, pinned_pat_hid) =
@@ -656,16 +674,19 @@ impl<'hir> LoweringContext<'_, 'hir> {
                 span,
                 hir::LangItem::PinNewUnchecked,
                 arena_vec![self; ref_mut_pinned],
+                Some(expr_hir_id),
             );
             let get_context = self.expr_call_lang_item_fn_mut(
                 gen_future_span,
                 hir::LangItem::GetContext,
                 arena_vec![self; task_context],
+                Some(expr_hir_id),
             );
             let call = self.expr_call_lang_item_fn(
                 span,
                 hir::LangItem::FuturePoll,
                 arena_vec![self; new_unchecked, get_context],
+                Some(expr_hir_id),
             );
             self.arena.alloc(self.expr_unsafe(call))
         };
@@ -678,18 +699,28 @@ impl<'hir> LoweringContext<'_, 'hir> {
             let (x_pat, x_pat_hid) = self.pat_ident(span, x_ident);
             let x_expr = self.expr_ident(span, x_ident, x_pat_hid);
             let ready_field = self.single_pat_field(span, x_pat);
-            let ready_pat = self.pat_lang_item_variant(span, hir::LangItem::PollReady, ready_field);
+            let ready_pat = self.pat_lang_item_variant(
+                span,
+                hir::LangItem::PollReady,
+                ready_field,
+                Some(expr_hir_id),
+            );
             let break_x = self.with_loop_scope(loop_node_id, move |this| {
                 let expr_break =
                     hir::ExprKind::Break(this.lower_loop_destination(None), Some(x_expr));
-                this.arena.alloc(this.expr(await_span, expr_break, ThinVec::new()))
+                this.arena.alloc(this.expr(span, expr_break, ThinVec::new()))
             });
             self.arm(ready_pat, break_x)
         };
 
         // `::std::task::Poll::Pending => {}`
         let pending_arm = {
-            let pending_pat = self.pat_lang_item_variant(span, hir::LangItem::PollPending, &[]);
+            let pending_pat = self.pat_lang_item_variant(
+                span,
+                hir::LangItem::PollPending,
+                &[],
+                Some(expr_hir_id),
+            );
             let empty_block = self.expr_block_empty(span);
             self.arm(pending_pat, empty_block)
         };
@@ -709,7 +740,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
             let unit = self.expr_unit(span);
             let yield_expr = self.expr(
                 span,
-                hir::ExprKind::Yield(unit, hir::YieldSource::Await { expr: Some(expr.hir_id) }),
+                hir::ExprKind::Yield(unit, hir::YieldSource::Await { expr: Some(expr_hir_id) }),
                 ThinVec::new(),
             );
             let yield_expr = self.arena.alloc(yield_expr);
@@ -756,6 +787,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
             into_future_span,
             hir::LangItem::IntoFutureIntoFuture,
             arena_vec![self; expr],
+            Some(expr_hir_id),
         );
 
         // match <into_future_expr> {
@@ -1160,7 +1192,8 @@ impl<'hir> LoweringContext<'_, 'hir> {
     fn lower_expr_range_closed(&mut self, span: Span, e1: &Expr, e2: &Expr) -> hir::ExprKind<'hir> {
         let e1 = self.lower_expr_mut(e1);
         let e2 = self.lower_expr_mut(e2);
-        let fn_path = hir::QPath::LangItem(hir::LangItem::RangeInclusiveNew, self.lower_span(span));
+        let fn_path =
+            hir::QPath::LangItem(hir::LangItem::RangeInclusiveNew, self.lower_span(span), None);
         let fn_expr =
             self.arena.alloc(self.expr(span, hir::ExprKind::Path(fn_path), ThinVec::new()));
         hir::ExprKind::Call(fn_expr, arena_vec![self; e1, e2])
@@ -1194,7 +1227,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
         );
 
         hir::ExprKind::Struct(
-            self.arena.alloc(hir::QPath::LangItem(lang_item, self.lower_span(span))),
+            self.arena.alloc(hir::QPath::LangItem(lang_item, self.lower_span(span), None)),
             fields,
             None,
         )
@@ -1389,6 +1422,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
                 head_span,
                 hir::LangItem::IteratorNext,
                 arena_vec![self; ref_mut_iter],
+                None,
             );
             let arms = arena_vec![self; none_arm, some_arm];
 
@@ -1417,6 +1451,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
                 head_span,
                 hir::LangItem::IntoIterIntoIter,
                 arena_vec![self; head],
+                None,
             )
         };
 
@@ -1472,6 +1507,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
                 unstable_span,
                 hir::LangItem::TryTraitBranch,
                 arena_vec![self; sub_expr],
+                None,
             )
         };
 
@@ -1628,8 +1664,10 @@ impl<'hir> LoweringContext<'_, 'hir> {
         span: Span,
         lang_item: hir::LangItem,
         args: &'hir [hir::Expr<'hir>],
+        hir_id: Option<hir::HirId>,
     ) -> hir::Expr<'hir> {
-        let path = self.arena.alloc(self.expr_lang_item_path(span, lang_item, ThinVec::new()));
+        let path =
+            self.arena.alloc(self.expr_lang_item_path(span, lang_item, ThinVec::new(), hir_id));
         self.expr_call_mut(span, path, args)
     }
 
@@ -1638,19 +1676,21 @@ impl<'hir> LoweringContext<'_, 'hir> {
         span: Span,
         lang_item: hir::LangItem,
         args: &'hir [hir::Expr<'hir>],
+        hir_id: Option<hir::HirId>,
     ) -> &'hir hir::Expr<'hir> {
-        self.arena.alloc(self.expr_call_lang_item_fn_mut(span, lang_item, args))
+        self.arena.alloc(self.expr_call_lang_item_fn_mut(span, lang_item, args, hir_id))
     }
 
     fn expr_lang_item_path(
         &mut self,
         span: Span,
         lang_item: hir::LangItem,
         attrs: AttrVec,
+        hir_id: Option<hir::HirId>,
     ) -> hir::Expr<'hir> {
         self.expr(
             span,
-            hir::ExprKind::Path(hir::QPath::LangItem(lang_item, self.lower_span(span))),
+            hir::ExprKind::Path(hir::QPath::LangItem(lang_item, self.lower_span(span), hir_id)),
             attrs,
         )
     }

compiler/rustc_ast_lowering/src/lib.rs

@@ -2127,21 +2127,21 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
 
     fn pat_cf_continue(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> {
         let field = self.single_pat_field(span, pat);
-        self.pat_lang_item_variant(span, hir::LangItem::ControlFlowContinue, field)
+        self.pat_lang_item_variant(span, hir::LangItem::ControlFlowContinue, field, None)
     }
 
     fn pat_cf_break(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> {
         let field = self.single_pat_field(span, pat);
-        self.pat_lang_item_variant(span, hir::LangItem::ControlFlowBreak, field)
+        self.pat_lang_item_variant(span, hir::LangItem::ControlFlowBreak, field, None)
     }
 
     fn pat_some(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> {
         let field = self.single_pat_field(span, pat);
-        self.pat_lang_item_variant(span, hir::LangItem::OptionSome, field)
+        self.pat_lang_item_variant(span, hir::LangItem::OptionSome, field, None)
     }
 
     fn pat_none(&mut self, span: Span) -> &'hir hir::Pat<'hir> {
-        self.pat_lang_item_variant(span, hir::LangItem::OptionNone, &[])
+        self.pat_lang_item_variant(span, hir::LangItem::OptionNone, &[], None)
     }
 
     fn single_pat_field(
@@ -2164,8 +2164,9 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         span: Span,
         lang_item: hir::LangItem,
         fields: &'hir [hir::PatField<'hir>],
+        hir_id: Option<hir::HirId>,
     ) -> &'hir hir::Pat<'hir> {
-        let qpath = hir::QPath::LangItem(lang_item, self.lower_span(span));
+        let qpath = hir::QPath::LangItem(lang_item, self.lower_span(span), hir_id);
         self.pat(span, hir::PatKind::Struct(qpath, fields, false))
     }
 

compiler/rustc_hir/src/hir.rs

@@ -1627,13 +1627,13 @@ pub fn is_range_literal(expr: &Expr<'_>) -> bool {
                     | LangItem::RangeFrom
                     | LangItem::RangeFull
                     | LangItem::RangeToInclusive,
-                _,
+                ..
             )
         ),
 
         // `..=` desugars into `::std::ops::RangeInclusive::new(...)`.
         ExprKind::Call(ref func, _) => {
-            matches!(func.kind, ExprKind::Path(QPath::LangItem(LangItem::RangeInclusiveNew, _)))
+            matches!(func.kind, ExprKind::Path(QPath::LangItem(LangItem::RangeInclusiveNew, ..)))
         }
 
         _ => false,
@@ -1788,8 +1788,8 @@ pub enum QPath<'hir> {
     /// the `X` and `Y` nodes each being a `TyKind::Path(QPath::TypeRelative(..))`.
     TypeRelative(&'hir Ty<'hir>, &'hir PathSegment<'hir>),
 
-    /// Reference to a `#[lang = "foo"]` item.
-    LangItem(LangItem, Span),
+    /// Reference to a `#[lang = "foo"]` item. `HirId` of the inner expr.
+    LangItem(LangItem, Span, Option<HirId>),
 }
 
 impl<'hir> QPath<'hir> {
@@ -1798,7 +1798,7 @@ impl<'hir> QPath<'hir> {
         match *self {
             QPath::Resolved(_, path) => path.span,
             QPath::TypeRelative(qself, ps) => qself.span.to(ps.ident.span),
-            QPath::LangItem(_, span) => span,
+            QPath::LangItem(_, span, _) => span,
         }
     }
 
@@ -1808,7 +1808,7 @@ impl<'hir> QPath<'hir> {
         match *self {
             QPath::Resolved(_, path) => path.span,
             QPath::TypeRelative(qself, _) => qself.span,
-            QPath::LangItem(_, span) => span,
+            QPath::LangItem(_, span, _) => span,
         }
     }
 
@@ -1818,7 +1818,7 @@ impl<'hir> QPath<'hir> {
         match *self {
             QPath::Resolved(_, path) => path.segments.last().unwrap().ident.span,
             QPath::TypeRelative(_, segment) => segment.ident.span,
-            QPath::LangItem(_, span) => span,
+            QPath::LangItem(_, span, _) => span,
         }
     }
 }

compiler/rustc_hir_pretty/src/lib.rs

@@ -1731,7 +1731,7 @@ impl<'a> State<'a> {
                     colons_before_params,
                 )
             }
-            hir::QPath::LangItem(lang_item, span) => {
+            hir::QPath::LangItem(lang_item, span, _) => {
                 self.word("#[lang = \"");
                 self.print_ident(Ident::new(lang_item.name(), span));
                 self.word("\"]");

compiler/rustc_lint/src/array_into_iter.rs

@@ -52,7 +52,7 @@ impl<'tcx> LateLintPass<'tcx> for ArrayIntoIter {
             if let hir::ExprKind::Call(path, [arg]) = &arg.kind {
                 if let hir::ExprKind::Path(hir::QPath::LangItem(
                     hir::LangItem::IntoIterIntoIter,
-                    _,
+                    ..,
                 )) = &path.kind
                 {
                     self.for_expr_span = arg.span;

compiler/rustc_middle/src/traits/mod.rs

@@ -348,6 +348,12 @@ pub enum ObligationCauseCode<'tcx> {
     /// If `X` is the concrete type of an opaque type `impl Y`, then `X` must implement `Y`
     OpaqueType,
 
+    AwaitableExpr(Option<hir::HirId>),
+
+    ForLoopIterator,
+
+    QuestionMark,
+
     /// Well-formed checking. If a `WellFormedLoc` is provided,
     /// then it will be used to eprform HIR-based wf checking
     /// after an error occurs, in order to generate a more precise error span.

compiler/rustc_passes/src/region.rs

@@ -421,11 +421,14 @@ fn resolve_expr<'tcx>(visitor: &mut RegionResolutionVisitor<'tcx>, expr: &'tcx h
         // Mark this expr's scope and all parent scopes as containing `yield`.
         let mut scope = Scope { id: expr.hir_id.local_id, data: ScopeData::Node };
         loop {
-            let data = YieldData {
-                span: expr.span,
-                expr_and_pat_count: visitor.expr_and_pat_count,
-                source: *source,
+            let span = match expr.kind {
+                hir::ExprKind::Yield(expr, hir::YieldSource::Await { .. }) => {
+                    expr.span.shrink_to_hi().to(expr.span)
+                }
+                _ => expr.span,
             };
+            let data =
+                YieldData { span, expr_and_pat_count: visitor.expr_and_pat_count, source: *source };
             visitor.scope_tree.yield_in_scope.insert(scope, data);
             if visitor.pessimistic_yield {
                 debug!("resolve_expr in pessimistic_yield - marking scope {:?} for fixup", scope);

compiler/rustc_save_analysis/src/sig.rs

@@ -286,7 +286,7 @@ impl<'hir> Sig for hir::Ty<'hir> {
                     refs: vec![SigElement { id, start, end }],
                 })
             }
-            hir::TyKind::Path(hir::QPath::LangItem(lang_item, _)) => {
+            hir::TyKind::Path(hir::QPath::LangItem(lang_item, _, _)) => {
                 Ok(text_sig(format!("#[lang = \"{}\"]", lang_item.name())))
             }
             hir::TyKind::TraitObject(bounds, ..) => {

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

@@ -439,6 +439,7 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
                         self.suggest_remove_reference(&obligation, &mut err, trait_ref);
                         self.suggest_semicolon_removal(&obligation, &mut err, span, trait_ref);
                         self.note_version_mismatch(&mut err, &trait_ref);
+                        self.suggest_remove_await(&obligation, &mut err);
 
                         if Some(trait_ref.def_id()) == tcx.lang_items().try_trait() {
                             self.suggest_await_before_try(&mut err, &obligation, trait_ref, span);