If the moved value is a mut reference, it is used in a generic function and it's type is a generic param, it can be reborrowed to avoid moving.

for example:

```rust
struct Y(u32);
// x's type is '& mut Y' and it is used in `fn generic<T>(x: T) {}`.
fn generic<T>(x: T) {}
```

fixes #127285

Author: surechen

compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs

@@ -204,16 +204,25 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, '_, 'infcx, 'tcx> {
                     is_loop_move = true;
                 }
 
+                let mut has_suggest_reborrow = false;
                 if !seen_spans.contains(&move_span) {
                     if !closure {
-                        self.suggest_ref_or_clone(mpi, &mut err, &mut in_pattern, move_spans);
+                        self.suggest_ref_or_clone(
+                            mpi,
+                            &mut err,
+                            &mut in_pattern,
+                            move_spans,
+                            moved_place.as_ref(),
+                            &mut has_suggest_reborrow,
+                        );
                     }
 
                     let msg_opt = CapturedMessageOpt {
                         is_partial_move,
                         is_loop_message,
                         is_move_msg,
                         is_loop_move,
+                        has_suggest_reborrow,
                         maybe_reinitialized_locations_is_empty: maybe_reinitialized_locations
                             .is_empty(),
                     };
@@ -258,17 +267,7 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, '_, 'infcx, 'tcx> {
             if is_loop_move & !in_pattern && !matches!(use_spans, UseSpans::ClosureUse { .. }) {
                 if let ty::Ref(_, _, hir::Mutability::Mut) = ty.kind() {
                     // We have a `&mut` ref, we need to reborrow on each iteration (#62112).
-                    err.span_suggestion_verbose(
-                        span.shrink_to_lo(),
-                        format!(
-                            "consider creating a fresh reborrow of {} here",
-                            self.describe_place(moved_place)
-                                .map(|n| format!("`{n}`"))
-                                .unwrap_or_else(|| "the mutable reference".to_string()),
-                        ),
-                        "&mut *",
-                        Applicability::MachineApplicable,
-                    );
+                    self.suggest_reborrow(&mut err, span, moved_place);
                 }
             }
 
@@ -345,6 +344,8 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, '_, 'infcx, 'tcx> {
         err: &mut Diag<'infcx>,
         in_pattern: &mut bool,
         move_spans: UseSpans<'tcx>,
+        moved_place: PlaceRef<'tcx>,
+        has_suggest_reborrow: &mut bool,
     ) {
         let move_span = match move_spans {
             UseSpans::ClosureUse { capture_kind_span, .. } => capture_kind_span,
@@ -434,20 +435,50 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, '_, 'infcx, 'tcx> {
                 let parent = self.infcx.tcx.parent_hir_node(expr.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)
+                    (typeck.type_dependent_def_id(parent_expr.hir_id), 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)
+                    (Some(*def_id), args, 0)
                 } else {
                     (None, &[][..], 0)
                 };
+
+                // If the moved value is a mut reference, it is used in a
+                // generic function and it's type is a generic param, it can be
+                // reborrowed to avoid moving.
+                // for example:
+                // struct Y(u32);
+                // x's type is '& mut Y' and it is used in `fn generic<T>(x: T) {}`.
+                let is_sugg_reborrow = || {
+                    if let Some(def_id) = def_id
+                        && self.infcx.tcx.def_kind(def_id).is_fn_like()
+                        && let Some(pos) = args.iter().position(|arg| arg.hir_id == expr.hir_id)
+                        && let ty::Param(_) =
+                            self.infcx.tcx.fn_sig(def_id).skip_binder().skip_binder().inputs()
+                                [pos + offset]
+                                .kind()
+                    {
+                        let place = &self.move_data.move_paths[mpi].place;
+                        let ty = place.ty(self.body, self.infcx.tcx).ty;
+                        if let ty::Ref(_, _, hir::Mutability::Mut) = ty.kind() {
+                            return true;
+                        }
+                    }
+                    false
+                };
+                *has_suggest_reborrow = is_sugg_reborrow();
+                if *has_suggest_reborrow {
+                    self.suggest_reborrow(err, expr.span, moved_place);
+                    return;
+                }
+
                 let mut can_suggest_clone = true;
                 if let Some(def_id) = def_id
-                    && let node = self.infcx.tcx.hir_node_by_def_id(def_id)
+                    && let Some(local_def_id) = def_id.as_local()
+                    && let node = self.infcx.tcx.hir_node_by_def_id(local_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)
@@ -561,6 +592,25 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, '_, 'infcx, 'tcx> {
         }
     }
 
+    pub fn suggest_reborrow(
+        &self,
+        err: &mut Diag<'infcx>,
+        span: Span,
+        moved_place: PlaceRef<'tcx>,
+    ) {
+        err.span_suggestion_verbose(
+            span.shrink_to_lo(),
+            format!(
+                "consider creating a fresh reborrow of {} here",
+                self.describe_place(moved_place)
+                    .map(|n| format!("`{n}`"))
+                    .unwrap_or_else(|| "the mutable reference".to_string()),
+            ),
+            "&mut *",
+            Applicability::MachineApplicable,
+        );
+    }
+
     fn report_use_of_uninitialized(
         &self,
         mpi: MovePathIndex,

compiler/rustc_borrowck/src/diagnostics/mod.rs

@@ -768,10 +768,11 @@ struct CapturedMessageOpt {
     is_loop_message: bool,
     is_move_msg: bool,
     is_loop_move: bool,
+    has_suggest_reborrow: bool,
     maybe_reinitialized_locations_is_empty: bool,
 }
 
-impl<'tcx> MirBorrowckCtxt<'_, '_, '_, 'tcx> {
+impl<'infcx, 'tcx> MirBorrowckCtxt<'_, '_, 'infcx, 'tcx> {
     /// Finds the spans associated to a move or copy of move_place at location.
     pub(super) fn move_spans(
         &self,
@@ -997,7 +998,7 @@ impl<'tcx> MirBorrowckCtxt<'_, '_, '_, 'tcx> {
     #[allow(rustc::untranslatable_diagnostic)] // FIXME: make this translatable
     fn explain_captures(
         &mut self,
-        err: &mut Diag<'_>,
+        err: &mut Diag<'infcx>,
         span: Span,
         move_span: Span,
         move_spans: UseSpans<'tcx>,
@@ -1009,6 +1010,7 @@ impl<'tcx> MirBorrowckCtxt<'_, '_, '_, 'tcx> {
             is_loop_message,
             is_move_msg,
             is_loop_move,
+            has_suggest_reborrow,
             maybe_reinitialized_locations_is_empty,
         } = msg_opt;
         if let UseSpans::FnSelfUse { var_span, fn_call_span, fn_span, kind } = move_spans {
@@ -1182,18 +1184,15 @@ impl<'tcx> MirBorrowckCtxt<'_, '_, '_, 'tcx> {
                         if let ty::Ref(_, _, hir::Mutability::Mut) =
                             moved_place.ty(self.body, self.infcx.tcx).ty.kind()
                         {
-                            // If we are in a loop this will be suggested later.
-                            if !is_loop_move {
-                                err.span_suggestion_verbose(
+                            // Suggest `reborrow` in other place for following situations:
+                            // 1. If we are in a loop this will be suggested later.
+                            // 2. If the moved value is a mut reference, it is used in a
+                            // generic function and the corresponding arg's type is generic param.
+                            if !is_loop_move && !has_suggest_reborrow {
+                                self.suggest_reborrow(
+                                    err,
                                     move_span.shrink_to_lo(),
-                                    format!(
-                                        "consider creating a fresh reborrow of {} here",
-                                        self.describe_place(moved_place.as_ref())
-                                            .map(|n| format!("`{n}`"))
-                                            .unwrap_or_else(|| "the mutable reference".to_string()),
-                                    ),
-                                    "&mut *",
-                                    Applicability::MachineApplicable,
+                                    moved_place.as_ref(),
                                 );
                             }
                         }

compiler/rustc_borrowck/src/diagnostics/move_errors.rs

@@ -554,6 +554,7 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, '_, 'infcx, 'tcx> {
             is_loop_message: false,
             is_move_msg: false,
             is_loop_move: false,
+            has_suggest_reborrow: false,
             maybe_reinitialized_locations_is_empty: true,
         };
         if let Some(use_spans) = use_spans {

tests/ui/borrowck/moved-value-suggest-reborrow-issue-127285.fixed

@@ -0,0 +1,17 @@
+//@ run-rustfix
+
+#![allow(dead_code)]
+
+struct X(u32);
+
+impl X {
+    fn f(&mut self) {
+        generic(&mut *self);
+        self.0 += 1;
+        //~^ ERROR: use of moved value: `self` [E0382]
+    }
+}
+
+fn generic<T>(_x: T) {}
+
+fn main() {}

tests/ui/borrowck/moved-value-suggest-reborrow-issue-127285.rs

@@ -0,0 +1,17 @@
+//@ run-rustfix
+
+#![allow(dead_code)]
+
+struct X(u32);
+
+impl X {
+    fn f(&mut self) {
+        generic(self);
+        self.0 += 1;
+        //~^ ERROR: use of moved value: `self` [E0382]
+    }
+}
+
+fn generic<T>(_x: T) {}
+
+fn main() {}

tests/ui/borrowck/moved-value-suggest-reborrow-issue-127285.stderr

@@ -0,0 +1,18 @@
+error[E0382]: use of moved value: `self`
+  --> $DIR/moved-value-suggest-reborrow-issue-127285.rs:10:9
+   |
+LL |     fn f(&mut self) {
+   |          --------- move occurs because `self` has type `&mut X`, which does not implement the `Copy` trait
+LL |         generic(self);
+   |                 ---- value moved here
+LL |         self.0 += 1;
+   |         ^^^^^^^^^^^ value used here after move
+   |
+help: consider creating a fresh reborrow of `self` here
+   |
+LL |         generic(&mut *self);
+   |                 ++++++
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0382`.

tests/ui/borrowck/mut-borrow-in-loop-2.stderr

@@ -8,19 +8,10 @@ LL |     for _ in 0..3 {
 LL |         Other::handle(value);
    |                       ^^^^^ value moved here, in previous iteration of loop
    |
-note: consider changing this parameter type in function `handle` to borrow instead if owning the value isn't necessary
-  --> $DIR/mut-borrow-in-loop-2.rs:8:22
-   |
-LL |     fn handle(value: T) -> Self;
-   |        ------        ^ this parameter takes ownership of the value
-   |        |
-   |        in this function
-help: consider moving the expression out of the loop so it is only moved once
-   |
-LL ~     let mut value = Other::handle(value);
-LL ~     for _ in 0..3 {
-LL ~         value;
+help: consider creating a fresh reborrow of `value` here
    |
+LL |         Other::handle(&mut *value);
+   |                       ++++++
 help: consider creating a fresh reborrow of `value` here
    |
 LL |         Other::handle(&mut *value);