Mention when type parameter could be Clone

```
error[E0382]: use of moved value: `t`
  --> $DIR/use_of_moved_value_copy_suggestions.rs:7:9
   |
LL | fn duplicate_t<T>(t: T) -> (T, T) {
   |                   - move occurs because `t` has type `T`, which does not implement the `Copy` trait
...
LL |     (t, t)
   |      -  ^ value used here after move
   |      |
   |      value moved here
   |
help: if `T` implemented `Clone`, you could clone the value
  --> $DIR/use_of_moved_value_copy_suggestions.rs:4:16
   |
LL | fn duplicate_t<T>(t: T) -> (T, T) {
   |                ^ consider constraining this type parameter with `Clone`
...
LL |     (t, t)
   |      - you could clone this value
help: consider restricting type parameter `T`
   |
LL | fn duplicate_t<T: Copy>(t: T) -> (T, T) {
   |                 ++++++
```

The `help` is new. On ADTs, we also extend the output with span labels:

```
error[E0507]: cannot move out of static item `FOO`
  --> $DIR/issue-17718-static-move.rs:6:14
   |
LL |     let _a = FOO;
   |              ^^^ move occurs because `FOO` has type `Foo`, which does not implement the `Copy` trait
   |
note: if `Foo` implemented `Clone`, you could clone the value
  --> $DIR/issue-17718-static-move.rs:1:1
   |
LL | struct Foo;
   | ^^^^^^^^^^ consider implementing `Clone` for this type
...
LL |     let _a = FOO;
   |              --- you could clone this value
help: consider borrowing here
   |
LL |     let _a = &FOO;
   |              +
```

Author: estebank

compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs

@@ -347,7 +347,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
         mpi: MovePathIndex,
         err: &mut Diag<'tcx>,
         in_pattern: &mut bool,
-        move_spans: UseSpans<'_>,
+        move_spans: UseSpans<'tcx>,
     ) {
         let move_span = match move_spans {
             UseSpans::ClosureUse { capture_kind_span, .. } => capture_kind_span,
@@ -491,11 +491,11 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                     ..
                 } = move_spans
                 {
-                    self.suggest_cloning(err, ty, expr, None);
+                    self.suggest_cloning(err, ty, expr, None, Some(move_spans));
                 } else if self.suggest_hoisting_call_outside_loop(err, expr) {
                     // The place where the the type moves would be misleading to suggest clone.
                     // #121466
-                    self.suggest_cloning(err, ty, expr, None);
+                    self.suggest_cloning(err, ty, expr, None, Some(move_spans));
                 }
             }
             if let Some(pat) = finder.pat {
@@ -1085,6 +1085,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
         ty: Ty<'tcx>,
         mut expr: &'cx hir::Expr<'cx>,
         mut other_expr: Option<&'cx hir::Expr<'cx>>,
+        use_spans: Option<UseSpans<'tcx>>,
     ) {
         if let hir::ExprKind::Struct(_, _, Some(_)) = expr.kind {
             // We have `S { foo: val, ..base }`. In `check_aggregate_rvalue` we have a single
@@ -1197,8 +1198,44 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                     .all(|field| self.implements_clone(field.ty(self.infcx.tcx, args)))
             })
         {
+            let ty_span = self.infcx.tcx.def_span(def.did());
+            let mut span: MultiSpan = ty_span.into();
+            span.push_span_label(ty_span, "consider implementing `Clone` for this type");
+            span.push_span_label(expr.span, "you could clone this value");
             err.span_note(
-                self.infcx.tcx.def_span(def.did()),
+                span,
+                format!("if `{ty}` implemented `Clone`, you could clone the value"),
+            );
+        } else if let ty::Param(param) = ty.kind()
+            && let Some(_clone_trait_def) = self.infcx.tcx.lang_items().clone_trait()
+            && let generics = self.infcx.tcx.generics_of(self.mir_def_id())
+            && let generic_param = generics.type_param(*param, self.infcx.tcx)
+            && let param_span = self.infcx.tcx.def_span(generic_param.def_id)
+            && if let Some(UseSpans::FnSelfUse { kind, .. }) = use_spans
+                && let CallKind::FnCall { fn_trait_id, self_ty } = kind
+                && let ty::Param(_) = self_ty.kind()
+                && ty == self_ty
+                && [
+                    self.infcx.tcx.lang_items().fn_once_trait(),
+                    self.infcx.tcx.lang_items().fn_mut_trait(),
+                    self.infcx.tcx.lang_items().fn_trait(),
+                ]
+                .contains(&Some(fn_trait_id))
+            {
+                // Do not suggest `F: FnOnce() + Clone`.
+                false
+            } else {
+                true
+            }
+        {
+            let mut span: MultiSpan = param_span.into();
+            span.push_span_label(
+                param_span,
+                "consider constraining this type parameter with `Clone`",
+            );
+            span.push_span_label(expr.span, "you could clone this value");
+            err.span_help(
+                span,
                 format!("if `{ty}` implemented `Clone`, you could clone the value"),
             );
         }
@@ -1403,7 +1440,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
         if let Some(expr) = self.find_expr(borrow_span)
             && let Some(ty) = typeck_results.node_type_opt(expr.hir_id)
         {
-            self.suggest_cloning(&mut err, ty, expr, self.find_expr(span));
+            self.suggest_cloning(&mut err, ty, expr, self.find_expr(span), Some(move_spans));
         }
         self.buffer_error(err);
     }

compiler/rustc_borrowck/src/diagnostics/move_errors.rs

@@ -447,7 +447,7 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
                     };
 
                     if let Some(expr) = self.find_expr(span) {
-                        self.suggest_cloning(err, place_ty, expr, self.find_expr(other_span));
+                        self.suggest_cloning(err, place_ty, expr, self.find_expr(other_span), None);
                     }
 
                     err.subdiagnostic(
@@ -482,7 +482,13 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
                 };
 
                 if let Some(expr) = self.find_expr(use_span) {
-                    self.suggest_cloning(err, place_ty, expr, self.find_expr(span));
+                    self.suggest_cloning(
+                        err,
+                        place_ty,
+                        expr,
+                        self.find_expr(span),
+                        Some(use_spans),
+                    );
                 }
 
                 err.subdiagnostic(
@@ -595,7 +601,7 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
                 let place_desc = &format!("`{}`", self.local_names[*local].unwrap());
 
                 if let Some(expr) = self.find_expr(binding_span) {
-                    self.suggest_cloning(err, bind_to.ty, expr, None);
+                    self.suggest_cloning(err, bind_to.ty, expr, None, None);
                 }
 
                 err.subdiagnostic(

tests/ui/associated-types/issue-25700.stderr

@@ -12,7 +12,10 @@ note: if `S<()>` implemented `Clone`, you could clone the value
   --> $DIR/issue-25700.rs:1:1
    |
 LL | struct S<T: 'static>(#[allow(dead_code)] Option<&'static T>);
-   | ^^^^^^^^^^^^^^^^^^^^
+   | ^^^^^^^^^^^^^^^^^^^^ consider implementing `Clone` for this type
+...
+LL |     drop(t);
+   |          - you could clone this value
 
 error: aborting due to 1 previous error
 

tests/ui/auto-traits/typeck-auto-trait-no-supertraits-2.stderr

@@ -23,6 +23,13 @@ LL | fn copy<T: Magic>(x: T) -> (T, T) { (x, x) }
    |                   |                  value moved here
    |                   move occurs because `x` has type `T`, which does not implement the `Copy` trait
    |
+help: if `T` implemented `Clone`, you could clone the value
+  --> $DIR/typeck-auto-trait-no-supertraits-2.rs:8:9
+   |
+LL | fn copy<T: Magic>(x: T) -> (T, T) { (x, x) }
+   |         ^                            - you could clone this value
+   |         |
+   |         consider constraining this type parameter with `Clone`
 help: consider further restricting this bound
    |
 LL | fn copy<T: Magic + Copy>(x: T) -> (T, T) { (x, x) }