Suggest .clone() or ref binding on E0382

compiler/rustc_ast/src/ast.rs

@@ -1376,7 +1376,7 @@ pub enum ExprKind {
     /// Conditionless loop (can be exited with `break`, `continue`, or `return`).
     ///
     /// `'label: loop { block }`
-    Loop(P<Block>, Option<Label>),
+    Loop(P<Block>, Option<Label>, Span),
     /// A `match` block.
     Match(P<Expr>, Vec<Arm>),
     /// A closure (e.g., `move |a, b, c| a + b + c`).

compiler/rustc_ast/src/mut_visit.rs

@@ -1355,9 +1355,10 @@ pub fn noop_visit_expr<T: MutVisitor>(
             vis.visit_block(body);
             visit_opt(label, |label| vis.visit_label(label));
         }
-        ExprKind::Loop(body, label) => {
+        ExprKind::Loop(body, label, span) => {
             vis.visit_block(body);
             visit_opt(label, |label| vis.visit_label(label));
+            vis.visit_span(span);
         }
         ExprKind::Match(expr, arms) => {
             vis.visit_expr(expr);

compiler/rustc_ast/src/visit.rs

@@ -824,7 +824,7 @@ pub fn walk_expr<'a, V: Visitor<'a>>(visitor: &mut V, expression: &'a Expr) {
             visitor.visit_expr(subexpression);
             visitor.visit_block(block);
         }
-        ExprKind::Loop(block, opt_label) => {
+        ExprKind::Loop(block, opt_label, _) => {
             walk_list!(visitor, visit_label, opt_label);
             visitor.visit_block(block);
         }

compiler/rustc_ast_lowering/src/expr.rs

@@ -131,12 +131,12 @@ impl<'hir> LoweringContext<'_, 'hir> {
                     let span = this.mark_span_with_reason(DesugaringKind::WhileLoop, e.span, None);
                     this.lower_expr_while_in_loop_scope(span, cond, body, *opt_label)
                 }),
-                ExprKind::Loop(body, opt_label) => self.with_loop_scope(e.id, |this| {
+                ExprKind::Loop(body, opt_label, span) => self.with_loop_scope(e.id, |this| {
                     hir::ExprKind::Loop(
                         this.lower_block(body, false),
                         this.lower_label(*opt_label),
                         hir::LoopSource::Loop,
-                        DUMMY_SP,
+                        this.lower_span(*span),
                     )
                 }),
                 ExprKind::TryBlock(body) => self.lower_expr_try_block(body),

compiler/rustc_ast_pretty/src/pprust/state/expr.rs

@@ -377,7 +377,7 @@ impl<'a> State<'a> {
                 self.space();
                 self.print_block_with_attrs(blk, attrs);
             }
-            ast::ExprKind::Loop(ref blk, opt_label) => {
+            ast::ExprKind::Loop(ref blk, opt_label, _) => {
                 if let Some(label) = opt_label {
                     self.print_ident(label.ident);
                     self.word_space(":");

compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs

@@ -167,10 +167,11 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                 );
             }
 
-            self.add_moved_or_invoked_closure_note(location, used_place, &mut err);
+            let closure = self.add_moved_or_invoked_closure_note(location, used_place, &mut err);
 
             let mut is_loop_move = false;
             let mut in_pattern = false;
+            let mut seen_spans = FxHashSet::default();
 
             for move_site in &move_site_vec {
                 let move_out = self.move_data.moves[(*move_site).moi];
@@ -191,37 +192,25 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                     is_loop_move = true;
                 }
 
-                self.explain_captures(
-                    &mut err,
-                    span,
-                    move_span,
-                    move_spans,
-                    *moved_place,
-                    partially_str,
-                    loop_message,
-                    move_msg,
-                    is_loop_move,
-                    maybe_reinitialized_locations.is_empty(),
-                );
-
-                if let (UseSpans::PatUse(span), []) =
-                    (move_spans, &maybe_reinitialized_locations[..])
-                {
-                    if maybe_reinitialized_locations.is_empty() {
-                        err.span_suggestion_verbose(
-                            span.shrink_to_lo(),
-                            &format!(
-                                "borrow this field in the pattern to avoid moving {}",
-                                self.describe_place(moved_place.as_ref())
-                                    .map(|n| format!("`{}`", n))
-                                    .unwrap_or_else(|| "the value".to_string())
-                            ),
-                            "ref ",
-                            Applicability::MachineApplicable,
-                        );
-                        in_pattern = true;
+                if !seen_spans.contains(&move_span) {
+                    if !closure {
+                        self.suggest_ref_or_clone(mpi, move_span, &mut err, &mut in_pattern);
                     }
+
+                    self.explain_captures(
+                        &mut err,
+                        span,
+                        move_span,
+                        move_spans,
+                        *moved_place,
+                        partially_str,
+                        loop_message,
+                        move_msg,
+                        is_loop_move,
+                        maybe_reinitialized_locations.is_empty(),
+                    );
                 }
+                seen_spans.insert(move_span);
             }
 
             use_spans.var_path_only_subdiag(&mut err, desired_action);
@@ -317,6 +306,160 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
         }
     }
 
+    fn suggest_ref_or_clone(
+        &mut self,
+        mpi: MovePathIndex,
+        move_span: Span,
+        err: &mut DiagnosticBuilder<'_, ErrorGuaranteed>,
+        in_pattern: &mut bool,
+    ) {
+        struct ExpressionFinder<'hir> {
+            expr_span: Span,
+            expr: Option<&'hir hir::Expr<'hir>>,
+            pat: Option<&'hir hir::Pat<'hir>>,
+            parent_pat: Option<&'hir hir::Pat<'hir>>,
+        }
+        impl<'hir> Visitor<'hir> for ExpressionFinder<'hir> {
+            fn visit_expr(&mut self, e: &'hir hir::Expr<'hir>) {
+                if e.span == self.expr_span {
+                    self.expr = Some(e);
+                }
+                hir::intravisit::walk_expr(self, e);
+            }
+            fn visit_pat(&mut self, p: &'hir hir::Pat<'hir>) {
+                if p.span == self.expr_span {
+                    self.pat = Some(p);
+                }
+                if let hir::PatKind::Binding(hir::BindingAnnotation::NONE, _, i, sub) = p.kind {
+                    if i.span == self.expr_span || p.span == self.expr_span {
+                        self.pat = Some(p);
+                    }
+                    // Check if we are in a situation of `ident @ ident` where we want to suggest
+                    // `ref ident @ ref ident` or `ref ident @ Struct { ref ident }`.
+                    if let Some(subpat) = sub && self.pat.is_none() {
+                        self.visit_pat(subpat);
+                        if self.pat.is_some() {
+                            self.parent_pat = Some(p);
+                        }
+                        return;
+                    }
+                }
+                hir::intravisit::walk_pat(self, p);
+            }
+        }
+        let hir = self.infcx.tcx.hir();
+        if let Some(hir::Node::Item(hir::Item {
+            kind: hir::ItemKind::Fn(_, _, body_id),
+            ..
+        })) = hir.find(hir.local_def_id_to_hir_id(self.mir_def_id()))
+            && let Some(hir::Node::Expr(expr)) = hir.find(body_id.hir_id)
+        {
+            let place = &self.move_data.move_paths[mpi].place;
+            let span = place.as_local()
+                .map(|local| self.body.local_decls[local].source_info.span);
+            let mut finder = ExpressionFinder {
+                expr_span: move_span,
+                expr: None,
+                pat: None,
+                parent_pat: None,
+            };
+            finder.visit_expr(expr);
+            if let Some(span) = span && let Some(expr) = finder.expr {
+                for (_, expr) in hir.parent_iter(expr.hir_id) {
+                    if let hir::Node::Expr(expr) = expr {
+                        if expr.span.contains(span) {
+                            // If the let binding occurs within the same loop, then that
+                            // loop isn't relevant, like in the following, the outermost `loop`
+                            // doesn't play into `x` being moved.
+                            // ```
+                            // loop {
+                            //     let x = String::new();
+                            //     loop {
+                            //         foo(x);
+                            //     }
+                            // }
+                            // ```
+                            break;
+                        }
+                        if let hir::ExprKind::Loop(.., loop_span) = expr.kind {
+                            err.span_label(loop_span, "inside of this loop");
+                        }
+                    }
+                }
+                let typeck = self.infcx.tcx.typeck(self.mir_def_id());
+                let hir_id = hir.get_parent_node(expr.hir_id);
+                if let Some(parent) = hir.find(hir_id) {
+                    let (def_id, args, offset) = if let hir::Node::Expr(parent_expr) = parent
+                        && let hir::ExprKind::MethodCall(_, _, args, _) = parent_expr.kind
+                        && let Some(def_id) = typeck.type_dependent_def_id(parent_expr.hir_id)
+                    {
+                        (def_id.as_local(), args, 1)
+                    } else if let hir::Node::Expr(parent_expr) = parent
+                        && let hir::ExprKind::Call(call, args) = parent_expr.kind
+                        && let ty::FnDef(def_id, _) = typeck.node_type(call.hir_id).kind()
+                    {
+                        (def_id.as_local(), args, 0)
+                    } else {
+                        (None, &[][..], 0)
+                    };
+                    if let Some(def_id) = def_id
+                        && let Some(node) = hir.find(hir.local_def_id_to_hir_id(def_id))
+                        && let Some(fn_sig) = node.fn_sig()
+                        && let Some(ident) = node.ident()
+                        && let Some(pos) = args.iter().position(|arg| arg.hir_id == expr.hir_id)
+                        && let Some(arg) = fn_sig.decl.inputs.get(pos + offset)
+                    {
+                        let mut span: MultiSpan = arg.span.into();
+                        span.push_span_label(
+                            arg.span,
+                            "this parameter takes ownership of the value".to_string(),
+                        );
+                        let descr = match node.fn_kind() {
+                            Some(hir::intravisit::FnKind::ItemFn(..)) | None => "function",
+                            Some(hir::intravisit::FnKind::Method(..)) => "method",
+                            Some(hir::intravisit::FnKind::Closure) => "closure",
+                        };
+                        span.push_span_label(
+                            ident.span,
+                            format!("in this {descr}"),
+                        );
+                        err.span_note(
+                            span,
+                            format!(
+                                "consider changing this parameter type in {descr} `{ident}` to \
+                                 borrow instead if owning the value isn't necessary",
+                            ),
+                        );
+                    }
+                    let place = &self.move_data.move_paths[mpi].place;
+                    let ty = place.ty(self.body, self.infcx.tcx).ty;
+                    if let hir::Node::Expr(parent_expr) = parent
+                        && let hir::ExprKind::Call(call_expr, _) = parent_expr.kind
+                        && let hir::ExprKind::Path(
+                            hir::QPath::LangItem(LangItem::IntoIterIntoIter, _, _)
+                        ) = call_expr.kind
+                    {
+                        // Do not suggest `.clone()` in a `for` loop, we already suggest borrowing.
+                    } else {
+                        self.suggest_cloning(err, ty, move_span);
+                    }
+                }
+            }
+            if let Some(pat) = finder.pat {
+                *in_pattern = true;
+                let mut sugg = vec![(pat.span.shrink_to_lo(), "ref ".to_string())];
+                if let Some(pat) = finder.parent_pat {
+                    sugg.insert(0, (pat.span.shrink_to_lo(), "ref ".to_string()));
+                }
+                err.multipart_suggestion_verbose(
+                    "borrow this binding in the pattern to avoid moving the value",
+                    sugg,
+                    Applicability::MachineApplicable,
+                );
+            }
+        }
+    }
+
     fn report_use_of_uninitialized(
         &self,
         mpi: MovePathIndex,
@@ -590,6 +733,27 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
         true
     }
 
+    fn suggest_cloning(&self, err: &mut Diagnostic, ty: Ty<'tcx>, span: Span) {
+        let tcx = self.infcx.tcx;
+        // Try to find predicates on *generic params* that would allow copying `ty`
+        let infcx = tcx.infer_ctxt().build();
+        if infcx
+            .type_implements_trait(
+                tcx.lang_items().clone_trait().unwrap(),
+                [tcx.erase_regions(ty)],
+                self.param_env,
+            )
+            .must_apply_modulo_regions()
+        {
+            err.span_suggestion_verbose(
+                span.shrink_to_hi(),
+                "consider cloning the value if the performance cost is acceptable",
+                ".clone()".to_string(),
+                Applicability::MachineApplicable,
+            );
+        }
+    }
+
     fn suggest_adding_copy_bounds(&self, err: &mut Diagnostic, ty: Ty<'tcx>, span: Span) {
         let tcx = self.infcx.tcx;
         let generics = tcx.generics_of(self.mir_def_id());

compiler/rustc_borrowck/src/diagnostics/mod.rs

@@ -70,7 +70,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
         location: Location,
         place: PlaceRef<'tcx>,
         diag: &mut Diagnostic,
-    ) {
+    ) -> bool {
         debug!("add_moved_or_invoked_closure_note: location={:?} place={:?}", location, place);
         let mut target = place.local_or_deref_local();
         for stmt in &self.body[location.block].statements[location.statement_index..] {
@@ -106,7 +106,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                         {
                             place.local_or_deref_local().unwrap()
                         }
-                        _ => return,
+                        _ => return false,
                     };
 
                     debug!("add_moved_or_invoked_closure_note: closure={:?}", closure);
@@ -125,7 +125,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                                     ty::place_to_string_for_capture(self.infcx.tcx, hir_place)
                                 ),
                             );
-                            return;
+                            return true;
                         }
                     }
                 }
@@ -149,9 +149,11 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                             ty::place_to_string_for_capture(self.infcx.tcx, hir_place)
                         ),
                     );
+                    return true;
                 }
             }
         }
+        false
     }
 
     /// End-user visible description of `place` if one can be found.

compiler/rustc_builtin_macros/src/assert/context.rs

@@ -307,7 +307,7 @@ impl<'cx, 'a> Context<'cx, 'a> {
             | ExprKind::InlineAsm(_)
             | ExprKind::Let(_, _, _)
             | ExprKind::Lit(_)
-            | ExprKind::Loop(_, _)
+            | ExprKind::Loop(_, _, _)
             | ExprKind::MacCall(_)
             | ExprKind::Match(_, _)
             | ExprKind::Path(_, _)

compiler/rustc_mir_build/src/thir/pattern/check_match.rs

@@ -1044,11 +1044,19 @@ fn check_borrow_conflicts_in_at_patterns(cx: &MatchVisitor<'_, '_, '_>, pat: &Pa
                     name,
                     typeck_results.node_type(pat.hir_id),
                 );
-                sess.struct_span_err(pat.span, "borrow of moved value")
-                    .span_label(binding_span, format!("value moved into `{}` here", name))
+                let mut err = sess.struct_span_err(pat.span, "borrow of moved value");
+                err.span_label(binding_span, format!("value moved into `{}` here", name))
                     .span_label(binding_span, occurs_because)
-                    .span_labels(conflicts_ref, "value borrowed here after move")
-                    .emit();
+                    .span_labels(conflicts_ref, "value borrowed here after move");
+                if pat.span.contains(binding_span) {
+                    err.span_suggestion_verbose(
+                        binding_span.shrink_to_lo(),
+                        "borrow this binding in the pattern to avoid moving the value",
+                        "ref ".to_string(),
+                        Applicability::MachineApplicable,
+                    );
+                }
+                err.emit();
             }
             return;
         }