Rollup merge of #71203 - csmoe:issue-71137, r=csmoe

Correct await span for async-await error reporting

Closes #71137
r? @tmandry

src/librustc_middle/ty/context.rs

@@ -298,14 +298,14 @@ pub struct ResolvedOpaqueTy<'tcx> {
 ///
 /// ```ignore (pseudo-Rust)
 /// async move {
-///     let x: T = ...;
+///     let x: T = expr;
 ///     foo.await
 ///     ...
 /// }
 /// ```
 ///
-/// Here, we would store the type `T`, the span of the value `x`, and the "scope-span" for
-/// the scope that contains `x`.
+/// Here, we would store the type `T`, the span of the value `x`, the "scope-span" for
+/// the scope that contains `x`, the expr `T` evaluated from, and the span of `foo.await`.
 #[derive(RustcEncodable, RustcDecodable, Clone, Debug, Eq, Hash, PartialEq, HashStable)]
 pub struct GeneratorInteriorTypeCause<'tcx> {
     /// Type of the captured binding.
@@ -314,6 +314,8 @@ pub struct GeneratorInteriorTypeCause<'tcx> {
     pub span: Span,
     /// Span of the scope of the captured binding.
     pub scope_span: Option<Span>,
+    /// Span of `.await` or `yield` expression.
+    pub yield_span: Span,
     /// Expr which the type evaluated from.
     pub expr: Option<hir::HirId>,
 }

src/librustc_trait_selection/traits/error_reporting/suggestions.rs

@@ -125,6 +125,7 @@ pub trait InferCtxtExt<'tcx> {
         err: &mut DiagnosticBuilder<'_>,
         target_span: Span,
         scope_span: &Option<Span>,
+        await_span: Span,
         expr: Option<hir::HirId>,
         snippet: String,
         inner_generator_body: Option<&hir::Body<'_>>,
@@ -1289,20 +1290,31 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
                         ty_matches(ty)
                     })
                     .map(|expr| expr.span);
-                let ty::GeneratorInteriorTypeCause { span, scope_span, expr, .. } = cause;
-                (span, source_map.span_to_snippet(*span), scope_span, expr, from_awaited_ty)
+                let ty::GeneratorInteriorTypeCause { span, scope_span, yield_span, expr, .. } =
+                    cause;
+                (
+                    span,
+                    source_map.span_to_snippet(*span),
+                    scope_span,
+                    yield_span,
+                    expr,
+                    from_awaited_ty,
+                )
             });
 
         debug!(
             "maybe_note_obligation_cause_for_async_await: target_ty={:?} \
                 generator_interior_types={:?} target_span={:?}",
             target_ty, tables.generator_interior_types, target_span
         );
-        if let Some((target_span, Ok(snippet), scope_span, expr, from_awaited_ty)) = target_span {
+        if let Some((target_span, Ok(snippet), scope_span, yield_span, expr, from_awaited_ty)) =
+            target_span
+        {
             self.note_obligation_cause_for_async_await(
                 err,
                 *target_span,
                 scope_span,
+                *yield_span,
                 *expr,
                 snippet,
                 generator_body,
@@ -1327,6 +1339,7 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
         err: &mut DiagnosticBuilder<'_>,
         target_span: Span,
         scope_span: &Option<Span>,
+        yield_span: Span,
         expr: Option<hir::HirId>,
         snippet: String,
         inner_generator_body: Option<&hir::Body<'_>>,
@@ -1418,10 +1431,9 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
                 "note_obligation_cause_for_async_await generator_interior_types: {:#?}",
                 tables.generator_interior_types
             );
-            let await_span = tables.generator_interior_types.iter().map(|t| t.span).last().unwrap();
-            let mut span = MultiSpan::from_span(await_span);
+            let mut span = MultiSpan::from_span(yield_span);
             span.push_span_label(
-                await_span,
+                yield_span,
                 format!("{} occurs here, with `{}` maybe used later", await_or_yield, snippet),
             );
 

src/librustc_typeck/check/generator_interior.rs

@@ -96,6 +96,7 @@ impl<'a, 'tcx> InteriorVisitor<'a, 'tcx> {
                         span: source_span,
                         ty: &ty,
                         scope_span,
+                        yield_span: yield_data.span,
                         expr: expr.map(|e| e.hir_id),
                     })
                     .or_insert(entries);

src/test/ui/async-await/issue-71137.rs

@@ -0,0 +1,21 @@
+// edition:2018
+
+use std::future::Future;
+use std::sync::Mutex;
+
+fn fake_spawn<F: Future + Send + 'static>(f: F) { }
+
+async fn wrong_mutex() {
+  let m = Mutex::new(1);
+  {
+    let mut guard = m.lock().unwrap();
+    (async { "right"; }).await;
+    *guard += 1;
+  }
+
+  (async { "wrong"; }).await;
+}
+
+fn main() {
+  fake_spawn(wrong_mutex()); //~ Error future cannot be sent between threads safely
+}

src/test/ui/async-await/issue-71137.stderr

@@ -0,0 +1,23 @@
+error: future cannot be sent between threads safely
+  --> $DIR/issue-71137.rs:20:3
+   |
+LL | fn fake_spawn<F: Future + Send + 'static>(f: F) { }
+   |                           ---- required by this bound in `fake_spawn`
+...
+LL |   fake_spawn(wrong_mutex());
+   |   ^^^^^^^^^^ future returned by `wrong_mutex` is not `Send`
+   |
+   = help: within `impl std::future::Future`, the trait `std::marker::Send` is not implemented for `std::sync::MutexGuard<'_, i32>`
+note: future is not `Send` as this value is used across an await
+  --> $DIR/issue-71137.rs:12:5
+   |
+LL |     let mut guard = m.lock().unwrap();
+   |         --------- has type `std::sync::MutexGuard<'_, i32>` which is not `Send`
+LL |     (async { "right"; }).await;
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^ await occurs here, with `mut guard` maybe used later
+LL |     *guard += 1;
+LL |   }
+   |   - `mut guard` is later dropped here
+
+error: aborting due to previous error
+