fix #104232, suggest clone for Arc/Rc

compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs

@@ -130,6 +130,10 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
             let partial_str = if is_partial_move { "partial " } else { "" };
             let partially_str = if is_partial_move { "partially " } else { "" };
 
+            let mpi = self.move_data.moves[move_out_indices[0]].path;
+            let place = &self.move_data.move_paths[mpi].place;
+            let ty = place.ty(self.body, self.infcx.tcx).ty;
+
             let mut err = self.cannot_act_on_moved_value(
                 span,
                 desired_action.as_noun(),
@@ -186,6 +190,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                 } else {
                     ""
                 };
+                let suggest_clone = self.suggest_using_clone(ty) && !move_spans.for_closure();
 
                 if location == move_out.source {
                     is_loop_move = true;
@@ -202,6 +207,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                     move_msg,
                     is_loop_move,
                     maybe_reinitialized_locations.is_empty(),
+                    suggest_clone,
                 );
 
                 if let (UseSpans::PatUse(span), []) =
@@ -237,8 +243,8 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                 );
             }
 
-            let ty = used_place.ty(self.body, self.infcx.tcx).ty;
-            let needs_note = match ty.kind() {
+            let used_ty = used_place.ty(self.body, self.infcx.tcx).ty;
+            let needs_note = match used_ty.kind() {
                 ty::Closure(id, _) => {
                     let tables = self.infcx.tcx.typeck(id.expect_local());
                     let hir_id = self.infcx.tcx.hir().local_def_id_to_hir_id(id.expect_local());
@@ -248,10 +254,6 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                 _ => true,
             };
 
-            let mpi = self.move_data.moves[move_out_indices[0]].path;
-            let place = &self.move_data.move_paths[mpi].place;
-            let ty = place.ty(self.body, self.infcx.tcx).ty;
-
             // If we're in pattern, we do nothing in favor of the previous suggestion (#80913).
             // Same for if we're in a loop, see #101119.
             if is_loop_move & !in_pattern && !matches!(use_spans, UseSpans::ClosureUse { .. }) {

compiler/rustc_borrowck/src/diagnostics/mod.rs

@@ -301,6 +301,16 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
         }
     }
 
+    /// We only suggest clone for `std::sync::Arc` and `std::rc::Rc` types.
+    fn suggest_using_clone(&self, ty: Ty<'tcx>) -> bool {
+        if let ty::Adt(adt, _) = ty.kind() &&
+            (self.infcx.tcx.is_diagnostic_item(sym::Arc, adt.did()) ||
+                self.infcx.tcx.is_diagnostic_item(sym::Rc, adt.did())) {
+                return true;
+            }
+        false
+    }
+
     /// End-user visible description of the `field`nth field of `base`
     fn describe_field(
         &self,
@@ -1029,6 +1039,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
         move_msg: &str,
         is_loop_move: bool,
         maybe_reinitialized_locations_is_empty: bool,
+        suggest_clone: bool,
     ) {
         if let UseSpans::FnSelfUse { var_span, fn_call_span, fn_span, kind } = move_spans {
             let place_name = self
@@ -1166,6 +1177,14 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                     move_span,
                     format!("value {}moved{} here{}", partially_str, move_msg, loop_message),
                 );
+                if suggest_clone {
+                    err.span_suggestion_verbose(
+                        move_span.shrink_to_hi(),
+                        "consider cloning here",
+                        ".clone()",
+                        Applicability::MaybeIncorrect,
+                    );
+                }
             }
             // If the move error occurs due to a loop, don't show
             // another message for the same span

compiler/rustc_borrowck/src/diagnostics/move_errors.rs

@@ -401,7 +401,7 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
         };
         if let Some(use_spans) = use_spans {
             self.explain_captures(
-                &mut err, span, span, use_spans, move_place, "", "", "", false, true,
+                &mut err, span, span, use_spans, move_place, "", "", "", false, true, false,
             );
         }
         err

src/test/ui/borrowck/issue-104232-suggest-clone.rs

@@ -0,0 +1,36 @@
+use std::sync::Arc;
+use std::rc::Rc;
+
+fn foo1(_: Arc<usize>) {}
+fn bar1(_: Arc<usize>) {}
+fn test_arc() {
+    let x = Arc::new(1);
+    foo1(x);
+    foo1(x); //~ ERROR use of moved value
+    bar1(x); //~ ERROR use of moved value
+}
+
+fn foo2(_: Rc<usize>) {}
+fn bar2(_: Rc<usize>) {}
+fn test_rc() {
+    let x = Rc::new(1);
+    foo2(x);
+    foo2(x); //~ ERROR use of moved value
+    bar2(x); //~ ERROR use of moved value
+}
+
+fn test_closure() {
+    let x = Arc::new(1);
+    for _ in 0..4 {
+        // Ideally we should suggest `let x = x.clone();` here.
+        std::thread::spawn(move || { //~ ERROR use of moved value
+            println!("{}", x);
+        });
+    }
+}
+
+fn main() {
+    test_rc();
+    test_arc();
+    test_closure();
+}

src/test/ui/borrowck/issue-104232-suggest-clone.stderr

@@ -0,0 +1,76 @@
+error[E0382]: use of moved value: `x`
+  --> $DIR/issue-104232-suggest-clone.rs:9:10
+   |
+LL |     let x = Arc::new(1);
+   |         - move occurs because `x` has type `Arc<usize>`, which does not implement the `Copy` trait
+LL |     foo1(x);
+   |          - value moved here
+LL |     foo1(x);
+   |          ^ value used here after move
+   |
+help: consider cloning here
+   |
+LL |     foo1(x.clone());
+   |           ++++++++
+
+error[E0382]: use of moved value: `x`
+  --> $DIR/issue-104232-suggest-clone.rs:10:10
+   |
+LL |     let x = Arc::new(1);
+   |         - move occurs because `x` has type `Arc<usize>`, which does not implement the `Copy` trait
+LL |     foo1(x);
+LL |     foo1(x);
+   |          - value moved here
+LL |     bar1(x);
+   |          ^ value used here after move
+   |
+help: consider cloning here
+   |
+LL |     foo1(x.clone());
+   |           ++++++++
+
+error[E0382]: use of moved value: `x`
+  --> $DIR/issue-104232-suggest-clone.rs:18:10
+   |
+LL |     let x = Rc::new(1);
+   |         - move occurs because `x` has type `Rc<usize>`, which does not implement the `Copy` trait
+LL |     foo2(x);
+   |          - value moved here
+LL |     foo2(x);
+   |          ^ value used here after move
+   |
+help: consider cloning here
+   |
+LL |     foo2(x.clone());
+   |           ++++++++
+
+error[E0382]: use of moved value: `x`
+  --> $DIR/issue-104232-suggest-clone.rs:19:10
+   |
+LL |     let x = Rc::new(1);
+   |         - move occurs because `x` has type `Rc<usize>`, which does not implement the `Copy` trait
+LL |     foo2(x);
+LL |     foo2(x);
+   |          - value moved here
+LL |     bar2(x);
+   |          ^ value used here after move
+   |
+help: consider cloning here
+   |
+LL |     foo2(x.clone());
+   |           ++++++++
+
+error[E0382]: use of moved value: `x`
+  --> $DIR/issue-104232-suggest-clone.rs:26:28
+   |
+LL |     let x = Arc::new(1);
+   |         - move occurs because `x` has type `Arc<i32>`, which does not implement the `Copy` trait
+...
+LL |         std::thread::spawn(move || {
+   |                            ^^^^^^^ value moved into closure here, in previous iteration of loop
+LL |             println!("{}", x);
+   |                            - use occurs due to use in closure
+
+error: aborting due to 5 previous errors
+
+For more information about this error, try `rustc --explain E0382`.

src/test/ui/moves/use_of_moved_value_clone_suggestions.stderr

@@ -7,6 +7,11 @@ LL |     (t, t)
    |      -  ^ value used here after move
    |      |
    |      value moved here
+   |
+help: consider cloning here
+   |
+LL |     (t.clone(), t)
+   |       ++++++++
 
 error: aborting due to previous error