Suggest to shorten temporary lifetime during method call inside generator

src/librustc/traits/error_reporting.rs

@@ -2456,7 +2456,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
         let target_span = tables
             .generator_interior_types
             .iter()
-            .find(|ty::GeneratorInteriorTypeCause { ty, .. }| {
+            .find(|(ty::GeneratorInteriorTypeCause { ty, .. }, _)| {
                 // Careful: the regions for types that appear in the
                 // generator interior are not generally known, so we
                 // want to erase them when comparing (and anyway,
@@ -2479,19 +2479,21 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
                 );
                 eq
             })
-            .map(|ty::GeneratorInteriorTypeCause { span, scope_span, .. }| {
-                (span, source_map.span_to_snippet(*span), scope_span)
+            .map(|(ty::GeneratorInteriorTypeCause { span, scope_span, .. }, expr)| {
+                (span, source_map.span_to_snippet(*span), scope_span, expr)
             });
+
         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)) = target_span {
+        if let Some((target_span, Ok(snippet), scope_span, expr)) = target_span {
             self.note_obligation_cause_for_async_await(
                 err,
                 *target_span,
                 scope_span,
+                *expr,
                 snippet,
                 generator_did,
                 last_generator,
@@ -2514,6 +2516,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
         err: &mut DiagnosticBuilder<'_>,
         target_span: Span,
         scope_span: &Option<Span>,
+        expr: Option<hir::HirId>,
         snippet: String,
         first_generator: DefId,
         last_generator: Option<DefId>,
@@ -2549,6 +2552,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
         // not implemented.
         let is_send = self.tcx.is_diagnostic_item(sym::send_trait, trait_ref.def_id);
         let is_sync = self.tcx.is_diagnostic_item(sym::sync_trait, trait_ref.def_id);
+        let hir = self.tcx.hir();
         let trait_explanation = if is_send || is_sync {
             let (trait_name, trait_verb) =
                 if is_send { ("`Send`", "sent") } else { ("`Sync`", "shared") };
@@ -2564,8 +2568,8 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
 
             let message = if let Some(name) = last_generator
                 .and_then(|generator_did| self.tcx.parent(generator_did))
-                .and_then(|parent_did| self.tcx.hir().as_local_hir_id(parent_did))
-                .and_then(|parent_hir_id| self.tcx.hir().opt_name(parent_hir_id))
+                .and_then(|parent_did| hir.as_local_hir_id(parent_did))
+                .and_then(|parent_hir_id| hir.opt_name(parent_hir_id))
             {
                 format!("future returned by `{}` is not {}", name, trait_name)
             } else {
@@ -2581,7 +2585,8 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
         };
 
         // Look at the last interior type to get a span for the `.await`.
-        let await_span = tables.generator_interior_types.iter().map(|i| i.span).last().unwrap();
+        let await_span =
+            tables.generator_interior_types.iter().map(|(i, _)| i.span).last().unwrap();
         let mut span = MultiSpan::from_span(await_span);
         span.push_span_label(
             await_span,
@@ -2606,6 +2611,22 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
             ),
         );
 
+        if let Some(expr_id) = expr {
+            let expr = hir.expect_expr(expr_id);
+            let is_ref = tables.expr_adjustments(expr).iter().any(|adj| adj.is_region_borrow());
+            let parent = hir.get_parent_node(expr_id);
+            if let Some(hir::Node::Expr(e)) = hir.find(parent) {
+                let method_span = hir.span(parent);
+                if tables.is_method_call(e) && is_ref {
+                    err.span_help(
+                        method_span,
+                        "consider moving this method call into a `let` \
+                        binding to create a shorter lived borrow",
+                    );
+                }
+            }
+        }
+
         // Add a note for the item obligation that remains - normally a note pointing to the
         // bound that introduced the obligation (e.g. `T: Send`).
         debug!("note_obligation_cause_for_async_await: next_code={:?}", next_code);

src/librustc/ty/adjustment.rs

@@ -81,6 +81,15 @@ pub struct Adjustment<'tcx> {
     pub target: Ty<'tcx>,
 }
 
+impl Adjustment<'tcx> {
+    pub fn is_region_borrow(&self) -> bool {
+        match self.kind {
+            Adjust::Borrow(AutoBorrow::Ref(..)) => true,
+            _ => false,
+        }
+    }
+}
+
 #[derive(Clone, Debug, RustcEncodable, RustcDecodable, HashStable, TypeFoldable)]
 pub enum Adjust<'tcx> {
     /// Go from ! to any type.

src/librustc/ty/context.rs

@@ -436,9 +436,9 @@ pub struct TypeckTables<'tcx> {
     /// entire variable.
     pub upvar_list: ty::UpvarListMap,
 
-    /// Stores the type, span and optional scope span of all types
+    /// Stores the type, expression, span and optional scope span of all types
     /// that are live across the yield of this generator (if a generator).
-    pub generator_interior_types: Vec<GeneratorInteriorTypeCause<'tcx>>,
+    pub generator_interior_types: Vec<(GeneratorInteriorTypeCause<'tcx>, Option<hir::HirId>)>,
 }
 
 impl<'tcx> TypeckTables<'tcx> {

src/librustc_typeck/check/generator_interior.rs

@@ -18,6 +18,7 @@ use rustc_span::Span;
 struct InteriorVisitor<'a, 'tcx> {
     fcx: &'a FnCtxt<'a, 'tcx>,
     types: FxHashMap<ty::GeneratorInteriorTypeCause<'tcx>, usize>,
+    exprs: Vec<Option<hir::HirId>>,
     region_scope_tree: &'tcx region::ScopeTree,
     expr_count: usize,
     kind: hir::GeneratorKind,
@@ -99,6 +100,7 @@ impl<'a, 'tcx> InteriorVisitor<'a, 'tcx> {
                         scope_span,
                     })
                     .or_insert(entries);
+                self.exprs.push(expr.map(|e| e.hir_id));
             }
         } else {
             debug!(
@@ -136,6 +138,7 @@ pub fn resolve_interior<'a, 'tcx>(
         expr_count: 0,
         kind,
         prev_unresolved_span: None,
+        exprs: vec![],
     };
     intravisit::walk_body(&mut visitor, body);
 
@@ -170,7 +173,8 @@ pub fn resolve_interior<'a, 'tcx>(
     });
 
     // Store the generator types and spans into the tables for this generator.
-    let interior_types = types.iter().map(|t| t.0.clone()).collect::<Vec<_>>();
+    let interior_types =
+        types.iter().zip(visitor.exprs).map(|(t, e)| (t.0.clone(), e)).collect::<Vec<_>>();
     visitor.fcx.inh.tables.borrow_mut().generator_interior_types = interior_types;
 
     // Extract type components

src/test/ui/async-await/issue-64130-4-async-move.stderr

@@ -16,6 +16,11 @@ LL |                 let _x = get().await;
 ...
 LL |     }
    |     - `client` is later dropped here
+help: consider moving this method call into a `let` binding to create a shorter lived borrow
+  --> $DIR/issue-64130-4-async-move.rs:19:15
+   |
+LL |         match client.status() {
+   |               ^^^^^^^^^^^^^^^
    = note: the return type of a function must have a statically known size
 
 error: aborting due to previous error