Mention type that could be Clone but isn't in more cases

estebank · estebank · commit 168cead1a102 · 2025-07-20T03:15:20.000Z
When encountering a moved value of a type that isn't `Clone` because of unmet obligations, but where all the unmet predicates reference crate-local types, mention them and suggest cloning, as we do in other cases already:

```
error[E0507]: cannot move out of `foo`, a captured variable in an `Fn` closure
  --&gt; f111.rs:14:25
   |
13 | fn do_stuff(foo: Option&lt;Foo&gt;) {
   |             --- captured outer variable
14 |     require_fn_trait(|| async {
   |                      -- ^^^^^ `foo` is moved here
   |                      |
   |                      captured by this `Fn` closure
15 |         if foo.map_or(false, |f| f.foo()) {
   |            ---
   |            |
   |            variable moved due to use in coroutine
   |            move occurs because `foo` has type `Option&lt;Foo&gt;`, which does not implement the `Copy` trait
   |
note: if `Foo` implemented `Clone`, you could clone the value
  --&gt; f111.rs:4:1
   |
4  | struct Foo;
   | ^^^^^^^^^^ consider implementing `Clone` for this type
...
15 |         if foo.map_or(false, |f| f.foo()) {
   |            --- you could clone this value
```
diff --git a/compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs b/compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs
@@ -1290,6 +1290,58 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
                 span,
                 format!("if `{ty}` implemented `Clone`, you could clone the value"),
             );
+        } else if let ty::Adt(_, _) = ty.kind()
+            && let Some(clone_trait) = self.infcx.tcx.lang_items().clone_trait()
+        {
+            // For cases like `Option<NonClone>`, where `Option<T>: Clone` if `T: Clone`, we point
+            // at the types that should be `Clone`.
+            let ocx = ObligationCtxt::new_with_diagnostics(self.infcx);
+            let cause = ObligationCause::misc(expr.span, self.mir_def_id());
+            ocx.register_bound(cause, self.infcx.param_env, ty, clone_trait);
+            let errors = ocx.select_all_or_error();
+            if errors.iter().all(|error| {
+                match error.obligation.predicate.as_clause().and_then(|c| c.as_trait_clause()) {
+                    Some(clause) => match clause.self_ty().skip_binder().kind() {
+                        ty::Adt(def, _) => def.did().is_local() && clause.def_id() == clone_trait,
+                        _ => false,
+                    },
+                    None => false,
+                }
+            }) {
+                let mut type_spans = vec![];
+                let mut types = FxIndexSet::default();
+                for clause in errors
+                    .iter()
+                    .filter_map(|e| e.obligation.predicate.as_clause())
+                    .filter_map(|c| c.as_trait_clause())
+                {
+                    let ty::Adt(def, _) = clause.self_ty().skip_binder().kind() else { continue };
+                    type_spans.push(self.infcx.tcx.def_span(def.did()));
+                    types.insert(
+                        self.infcx
+                            .tcx
+                            .short_string(clause.self_ty().skip_binder(), &mut err.long_ty_path()),
+                    );
+                }
+                let mut span: MultiSpan = type_spans.clone().into();
+                for sp in type_spans {
+                    span.push_span_label(sp, "consider implementing `Clone` for this type");
+                }
+                span.push_span_label(expr.span, "you could clone this value");
+                let types: Vec<_> = types.into_iter().collect();
+                let msg = match &types[..] {
+                    [only] => format!("`{only}`"),
+                    [head @ .., last] => format!(
+                        "{} and `{last}`",
+                        head.iter().map(|t| format!("`{t}`")).collect::<Vec<_>>().join(", ")
+                    ),
+                    [] => unreachable!(),
+                };
+                err.span_note(
+                    span,
+                    format!("if {msg} implemented `Clone`, you could clone the value"),
+                );
+            }
         }
     }
 
diff --git a/tests/ui/borrowck/borrowck-partial-reinit-1.stderr b/tests/ui/borrowck/borrowck-partial-reinit-1.stderr
@@ -8,6 +8,15 @@ LL |     drop(t);
    |          - value moved here
 LL |     t.b = Some(u);
    |     ^^^ value assigned here after move
+   |
+note: if `Test2` implemented `Clone`, you could clone the value
+  --> $DIR/borrowck-partial-reinit-1.rs:3:1
+   |
+LL | struct Test2 {
+   | ^^^^^^^^^^^^ consider implementing `Clone` for this type
+...
+LL |     drop(t);
+   |          - you could clone this value
 
 error[E0382]: assign of moved value: `t`
   --> $DIR/borrowck-partial-reinit-1.rs:33:5
@@ -19,6 +28,15 @@ LL |     drop(t);
    |          - value moved here
 LL |     t.0 = Some(u);
    |     ^^^ value assigned here after move
+   |
+note: if `Test3` implemented `Clone`, you could clone the value
+  --> $DIR/borrowck-partial-reinit-1.rs:7:1
+   |
+LL | struct Test3(Option<Test>);
+   | ^^^^^^^^^^^^ consider implementing `Clone` for this type
+...
+LL |     drop(t);
+   |          - you could clone this value
 
 error: aborting due to 2 previous errors
 
diff --git a/tests/ui/borrowck/borrowck-partial-reinit-2.stderr b/tests/ui/borrowck/borrowck-partial-reinit-2.stderr
@@ -7,6 +7,15 @@ LL |     let mut u = Test { a: 2, b: Some(Box::new(t))};
    |                                               - value moved here
 LL |     t.b = Some(Box::new(u));
    |     ^^^ value assigned here after move
+   |
+note: if `Test` implemented `Clone`, you could clone the value
+  --> $DIR/borrowck-partial-reinit-2.rs:1:1
+   |
+LL | struct Test {
+   | ^^^^^^^^^^^ consider implementing `Clone` for this type
+...
+LL |     let mut u = Test { a: 2, b: Some(Box::new(t))};
+   |                                               - you could clone this value
 
 error: aborting due to 1 previous error
 
diff --git a/tests/ui/borrowck/borrowck-union-move-assign.stderr b/tests/ui/borrowck/borrowck-union-move-assign.stderr
@@ -7,6 +7,15 @@ LL |             let a = u.a;
    |                     --- value moved here
 LL |             let a = u.a;
    |                     ^^^ value used here after move
+   |
+note: if `U` implemented `Clone`, you could clone the value
+  --> $DIR/borrowck-union-move-assign.rs:7:1
+   |
+LL | union U {
+   | ^^^^^^^ consider implementing `Clone` for this type
+...
+LL |             let a = u.a;
+   |                     --- you could clone this value
 
 error: aborting due to 1 previous error
 
diff --git a/tests/ui/borrowck/borrowck-union-move.stderr b/tests/ui/borrowck/borrowck-union-move.stderr
@@ -7,6 +7,15 @@ LL |             let a = u.n1;
    |                     ---- value moved here
 LL |             let a = u.n1;
    |                     ^^^^ value used here after move
+   |
+note: if `Unn` implemented `Clone`, you could clone the value
+  --> $DIR/borrowck-union-move.rs:7:1
+   |
+LL | union Unn {
+   | ^^^^^^^^^ consider implementing `Clone` for this type
+...
+LL |             let a = u.n1;
+   |                     ---- you could clone this value
 
 error[E0382]: use of moved value: `u`
   --> $DIR/borrowck-union-move.rs:31:21
@@ -17,6 +26,15 @@ LL |             let a = u.n1;
    |                     ---- value moved here
 LL |             let a = u;
    |                     ^ value used here after move
+   |
+note: if `Unn` implemented `Clone`, you could clone the value
+  --> $DIR/borrowck-union-move.rs:7:1
+   |
+LL | union Unn {
+   | ^^^^^^^^^ consider implementing `Clone` for this type
+...
+LL |             let a = u.n1;
+   |                     ---- you could clone this value
 
 error[E0382]: use of moved value: `u`
   --> $DIR/borrowck-union-move.rs:36:21
@@ -27,6 +45,15 @@ LL |             let a = u.n1;
    |                     ---- value moved here
 LL |             let a = u.n2;
    |                     ^^^^ value used here after move
+   |
+note: if `Unn` implemented `Clone`, you could clone the value
+  --> $DIR/borrowck-union-move.rs:7:1
+   |
+LL | union Unn {
+   | ^^^^^^^^^ consider implementing `Clone` for this type
+...
+LL |             let a = u.n1;
+   |                     ---- you could clone this value
 
 error[E0382]: use of moved value: `u`
   --> $DIR/borrowck-union-move.rs:63:21
@@ -37,6 +64,15 @@ LL |             let a = u.n;
    |                     --- value moved here
 LL |             let a = u.n;
    |                     ^^^ value used here after move
+   |
+note: if `Ucn` implemented `Clone`, you could clone the value
+  --> $DIR/borrowck-union-move.rs:15:1
+   |
+LL | union Ucn {
+   | ^^^^^^^^^ consider implementing `Clone` for this type
+...
+LL |             let a = u.n;
+   |                     --- you could clone this value
 
 error[E0382]: use of moved value: `u`
   --> $DIR/borrowck-union-move.rs:68:21
@@ -47,6 +83,15 @@ LL |             let a = u.n;
    |                     --- value moved here
 LL |             let a = u.c;
    |                     ^^^ value used here after move
+   |
+note: if `Ucn` implemented `Clone`, you could clone the value
+  --> $DIR/borrowck-union-move.rs:15:1
+   |
+LL | union Ucn {
+   | ^^^^^^^^^ consider implementing `Clone` for this type
+...
+LL |             let a = u.n;
+   |                     --- you could clone this value
 
 error[E0382]: use of moved value: `u`
   --> $DIR/borrowck-union-move.rs:83:21
@@ -57,6 +102,15 @@ LL |             let a = u.n;
    |                     --- value moved here
 LL |             let a = u;
    |                     ^ value used here after move
+   |
+note: if `Ucn` implemented `Clone`, you could clone the value
+  --> $DIR/borrowck-union-move.rs:15:1
+   |
+LL | union Ucn {
+   | ^^^^^^^^^ consider implementing `Clone` for this type
+...
+LL |             let a = u.n;
+   |                     --- you could clone this value
 
 error: aborting due to 6 previous errors
 
diff --git a/tests/ui/borrowck/issue-54499-field-mutation-of-moved-out-with-mut.stderr b/tests/ui/borrowck/issue-54499-field-mutation-of-moved-out-with-mut.stderr
@@ -17,6 +17,15 @@ LL |         drop(u);
    |              - value moved here
 LL |         u.0 = S(1);
    |         ^^^^^^^^^^ value partially assigned here after move
+   |
+note: if `Tpair` implemented `Clone`, you could clone the value
+  --> $DIR/issue-54499-field-mutation-of-moved-out-with-mut.rs:6:1
+   |
+LL | struct Tpair(S, i32);
+   | ^^^^^^^^^^^^ consider implementing `Clone` for this type
+...
+LL |         drop(u);
+   |              - you could clone this value
 
 error[E0382]: assign to part of moved value: `v`
   --> $DIR/issue-54499-field-mutation-of-moved-out-with-mut.rs:31:9
@@ -27,6 +36,15 @@ LL |         drop(v);
    |              - value moved here
 LL |         v.x = S(1);
    |         ^^^^^^^^^^ value partially assigned here after move
+   |
+note: if `Spair` implemented `Clone`, you could clone the value
+  --> $DIR/issue-54499-field-mutation-of-moved-out-with-mut.rs:7:1
+   |
+LL | struct Spair { x: S, y: i32 }
+   | ^^^^^^^^^^^^ consider implementing `Clone` for this type
+...
+LL |         drop(v);
+   |              - you could clone this value
 
 error: aborting due to 3 previous errors
 
diff --git a/tests/ui/borrowck/issue-54499-field-mutation-of-moved-out.stderr b/tests/ui/borrowck/issue-54499-field-mutation-of-moved-out.stderr
@@ -50,6 +50,15 @@ LL |         drop(u);
    |              - value moved here
 LL |         u.0 = S(1);
    |         ^^^^^^^^^^ value partially assigned here after move
+   |
+note: if `Tpair` implemented `Clone`, you could clone the value
+  --> $DIR/issue-54499-field-mutation-of-moved-out.rs:6:1
+   |
+LL | struct Tpair(S, i32);
+   | ^^^^^^^^^^^^ consider implementing `Clone` for this type
+...
+LL |         drop(u);
+   |              - you could clone this value
 
 error[E0594]: cannot assign to `u.1`, as `u` is not declared as mutable
   --> $DIR/issue-54499-field-mutation-of-moved-out.rs:27:9
@@ -82,6 +91,15 @@ LL |         drop(v);
    |              - value moved here
 LL |         v.x = S(1);
    |         ^^^^^^^^^^ value partially assigned here after move
+   |
+note: if `Spair` implemented `Clone`, you could clone the value
+  --> $DIR/issue-54499-field-mutation-of-moved-out.rs:7:1
+   |
+LL | struct Spair { x: S, y: i32 }
+   | ^^^^^^^^^^^^ consider implementing `Clone` for this type
+...
+LL |         drop(v);
+   |              - you could clone this value
 
 error[E0594]: cannot assign to `v.y`, as `v` is not declared as mutable
   --> $DIR/issue-54499-field-mutation-of-moved-out.rs:38:9
diff --git a/tests/ui/borrowck/issue-54597-reject-move-out-of-borrow-via-pat.stderr b/tests/ui/borrowck/issue-54597-reject-move-out-of-borrow-via-pat.stderr
@@ -4,6 +4,14 @@ error[E0507]: cannot move out of `*array` which is behind a shared reference
 LL |             *array
    |             ^^^^^^ move occurs because `*array` has type `Vec<Value>`, which does not implement the `Copy` trait
    |
+note: if `Value` implemented `Clone`, you could clone the value
+  --> $DIR/issue-54597-reject-move-out-of-borrow-via-pat.rs:4:1
+   |
+LL | struct Value;
+   | ^^^^^^^^^^^^ consider implementing `Clone` for this type
+...
+LL |             *array
+   |             ------ you could clone this value
 help: consider removing the dereference here
    |
 LL -             *array
diff --git a/tests/ui/closures/2229_closure_analysis/match/if-let-guards-errors.e2018.stderr b/tests/ui/closures/2229_closure_analysis/match/if-let-guards-errors.e2018.stderr
@@ -26,6 +26,15 @@ LL |             E::Number(_) if let E::String(s) = *value => { }
 ...
 LL |     let x = value;
    |             ^^^^^ value used here after move
+   |
+note: if `E` implemented `Clone`, you could clone the value
+  --> $DIR/if-let-guards-errors.rs:32:1
+   |
+LL |             E::Number(_) if let E::String(s) = *value => { }
+   |                                                ------ you could clone this value
+...
+LL | enum E {
+   | ^^^^^^ consider implementing `Clone` for this type
 
 error: aborting due to 2 previous errors
 
diff --git a/tests/ui/closures/2229_closure_analysis/match/if-let-guards-errors.e2021.stderr b/tests/ui/closures/2229_closure_analysis/match/if-let-guards-errors.e2021.stderr
@@ -26,6 +26,15 @@ LL |             E::Number(_) if let E::String(s) = *value => { }
 ...
 LL |     let x = value;
    |             ^^^^^ value used here after move
+   |
+note: if `E` implemented `Clone`, you could clone the value
+  --> $DIR/if-let-guards-errors.rs:32:1
+   |
+LL |             E::Number(_) if let E::String(s) = *value => { }
+   |                                                ------ you could clone this value
+...
+LL | enum E {
+   | ^^^^^^ consider implementing `Clone` for this type
 
 error: aborting due to 2 previous errors
 
diff --git a/tests/ui/moves/suggest-clone-when-some-obligation-is-unmet.stderr b/tests/ui/moves/suggest-clone-when-some-obligation-is-unmet.stderr
@@ -8,6 +8,14 @@ LL |     let mut copy: Vec<U> = map.clone().into_values().collect();
    |
 note: `HashMap::<K, V, S>::into_values` takes ownership of the receiver `self`, which moves value
   --> $SRC_DIR/std/src/collections/hash/map.rs:LL:COL
+note: if `Hash128_1` implemented `Clone`, you could clone the value
+  --> $DIR/suggest-clone-when-some-obligation-is-unmet.rs:8:1
+   |
+LL | pub struct Hash128_1;
+   | ^^^^^^^^^^^^^^^^^^^^ consider implementing `Clone` for this type
+...
+LL |     let mut copy: Vec<U> = map.clone().into_values().collect();
+   |                            ----------- you could clone this value
 help: you could `clone` the value and consume it, if the `Hash128_1: Clone` trait bound could be satisfied
    |
 LL -     let mut copy: Vec<U> = map.clone().into_values().collect();
diff --git a/tests/ui/nll/issue-21232-partial-init-and-erroneous-use.stderr b/tests/ui/nll/issue-21232-partial-init-and-erroneous-use.stderr
@@ -27,6 +27,15 @@ LL |     drop(d);
    |          - value moved here
 LL |     d.x = 10;
    |     ^^^^^^^^ value assigned here after move
+   |
+note: if `D` implemented `Clone`, you could clone the value
+  --> $DIR/issue-21232-partial-init-and-erroneous-use.rs:11:1
+   |
+LL | struct D {
+   | ^^^^^^^^ consider implementing `Clone` for this type
+...
+LL |     drop(d);
+   |          - you could clone this value
 
 error[E0381]: partially assigned binding `d` isn't fully initialized
   --> $DIR/issue-21232-partial-init-and-erroneous-use.rs:45:5
@@ -57,6 +66,15 @@ LL |     drop(d);
    |          - value moved here
 LL |     d.s.y = 20;
    |     ^^^^^^^^^^ value partially assigned here after move
+   |
+note: if `D` implemented `Clone`, you could clone the value
+  --> $DIR/issue-21232-partial-init-and-erroneous-use.rs:11:1
+   |
+LL | struct D {
+   | ^^^^^^^^ consider implementing `Clone` for this type
+...
+LL |     drop(d);
+   |          - you could clone this value
 
 error: aborting due to 6 previous errors
 
diff --git a/tests/ui/pattern/move-ref-patterns/move-ref-patterns-closure-captures-inside.stderr b/tests/ui/pattern/move-ref-patterns/move-ref-patterns-closure-captures-inside.stderr
diff --git a/tests/ui/static/static-items-cant-move.stderr b/tests/ui/static/static-items-cant-move.stderr
diff --git a/tests/ui/suggestions/option-content-move2.stderr b/tests/ui/suggestions/option-content-move2.stderr
diff --git a/tests/ui/union/union-borrow-move-parent-sibling.stderr b/tests/ui/union/union-borrow-move-parent-sibling.stderr
diff --git a/tests/ui/unsafe-binders/moves.stderr b/tests/ui/unsafe-binders/moves.stderr
diff --git a/tests/ui/use/use-after-move-implicity-coerced-object.stderr b/tests/ui/use/use-after-move-implicity-coerced-object.stderr
