Auto merge of #89263 - TaKO8Ki:suggest-both-immutable-and-mutable-trait-implementations, r=estebank

Suggest both of immutable and mutable trait implementations

closes #85865

12 files changed, 211 insertions, 92 deletions

diff --git a/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs b/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs
index 9d1f409d69c..2a51e014713 100644
--- a/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs
+++ b/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs
@@ -714,22 +714,28 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
         let mut_substs = self.tcx.mk_substs_trait(mut_borrowed_found_ty, &[]);
 
         // Try to apply the original trait binding obligation by borrowing.
-        let mut try_borrowing = |new_trait_ref: ty::TraitRef<'tcx>,
+        let mut try_borrowing = |new_imm_trait_ref: ty::TraitRef<'tcx>,
+                                 new_mut_trait_ref: ty::TraitRef<'tcx>,
                                  expected_trait_ref: ty::TraitRef<'tcx>,
-                                 mtbl: bool,
                                  blacklist: &[DefId]|
          -> bool {
             if blacklist.contains(&expected_trait_ref.def_id) {
                 return false;
             }
 
-            let new_obligation = Obligation::new(
+            let imm_result = self.predicate_must_hold_modulo_regions(&Obligation::new(
                 ObligationCause::dummy(),
                 param_env,
-                ty::Binder::dummy(new_trait_ref).without_const().to_predicate(self.tcx),
-            );
+                ty::Binder::dummy(new_imm_trait_ref).without_const().to_predicate(self.tcx),
+            ));
 
-            if self.predicate_must_hold_modulo_regions(&new_obligation) {
+            let mut_result = self.predicate_must_hold_modulo_regions(&Obligation::new(
+                ObligationCause::dummy(),
+                param_env,
+                ty::Binder::dummy(new_mut_trait_ref).without_const().to_predicate(self.tcx),
+            ));
+
+            if imm_result || mut_result {
                 if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(span) {
                     // We have a very specific type of error, where just borrowing this argument
                     // might solve the problem. In cases like this, the important part is the
@@ -773,15 +779,24 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
                         // }
                         // ```
 
-                        err.span_suggestion(
-                            span,
-                            &format!(
-                                "consider{} borrowing here",
-                                if mtbl { " mutably" } else { "" }
-                            ),
-                            format!("&{}{}", if mtbl { "mut " } else { "" }, snippet),
-                            Applicability::MaybeIncorrect,
-                        );
+                        if imm_result && mut_result {
+                            err.span_suggestions(
+                                span.shrink_to_lo(),
+                                "consider borrowing here",
+                                ["&".to_string(), "&mut ".to_string()].into_iter(),
+                                Applicability::MaybeIncorrect,
+                            );
+                        } else {
+                            err.span_suggestion_verbose(
+                                span.shrink_to_lo(),
+                                &format!(
+                                    "consider{} borrowing here",
+                                    if mut_result { " mutably" } else { "" }
+                                ),
+                                format!("&{}", if mut_result { "mut " } else { "" }),
+                                Applicability::MaybeIncorrect,
+                            );
+                        }
                     }
                     return true;
                 }
@@ -795,29 +810,16 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
                 ty::TraitRef::new(obligation.parent_trait_ref.def_id(), imm_substs);
             let new_mut_trait_ref =
                 ty::TraitRef::new(obligation.parent_trait_ref.def_id(), mut_substs);
-            if try_borrowing(new_imm_trait_ref, expected_trait_ref, false, &[]) {
-                return true;
-            } else {
-                return try_borrowing(new_mut_trait_ref, expected_trait_ref, true, &[]);
-            }
+            return try_borrowing(new_imm_trait_ref, new_mut_trait_ref, expected_trait_ref, &[]);
         } else if let ObligationCauseCode::BindingObligation(_, _)
         | ObligationCauseCode::ItemObligation(_) = &*code
         {
-            if try_borrowing(
+            return try_borrowing(
                 ty::TraitRef::new(trait_ref.def_id, imm_substs),
+                ty::TraitRef::new(trait_ref.def_id, mut_substs),
                 trait_ref,
-                false,
                 &never_suggest_borrow[..],
-            ) {
-                return true;
-            } else {
-                return try_borrowing(
-                    ty::TraitRef::new(trait_ref.def_id, mut_substs),
-                    trait_ref,
-                    true,
-                    &never_suggest_borrow[..],
-                );
-            }
+            );
         } else {
             false
         }
diff --git a/src/test/ui/derives/deriving-copyclone.stderr b/src/test/ui/derives/deriving-copyclone.stderr
index 2538b5533a6..1d0554ad047 100644
--- a/src/test/ui/derives/deriving-copyclone.stderr
+++ b/src/test/ui/derives/deriving-copyclone.stderr
@@ -2,10 +2,8 @@ error[E0277]: the trait bound `C: Copy` is not satisfied
   --> $DIR/deriving-copyclone.rs:31:13
    |
 LL |     is_copy(B { a: 1, b: C });
-   |     ------- ^^^^^^^^^^^^^^^^
-   |     |       |
-   |     |       expected an implementor of trait `Copy`
-   |     |       help: consider borrowing here: `&B { a: 1, b: C }`
+   |     ------- ^^^^^^^^^^^^^^^^ expected an implementor of trait `Copy`
+   |     |
    |     required by a bound introduced by this call
    |
 note: required because of the requirements on the impl of `Copy` for `B<C>`
@@ -19,15 +17,17 @@ note: required by a bound in `is_copy`
 LL | fn is_copy<T: Copy>(_: T) {}
    |               ^^^^ required by this bound in `is_copy`
    = note: this error originates in the derive macro `Copy` (in Nightly builds, run with -Z macro-backtrace for more info)
+help: consider borrowing here
+   |
+LL |     is_copy(&B { a: 1, b: C });
+   |             +
 
 error[E0277]: the trait bound `C: Clone` is not satisfied
   --> $DIR/deriving-copyclone.rs:32:14
    |
 LL |     is_clone(B { a: 1, b: C });
-   |     -------- ^^^^^^^^^^^^^^^^
-   |     |        |
-   |     |        expected an implementor of trait `Clone`
-   |     |        help: consider borrowing here: `&B { a: 1, b: C }`
+   |     -------- ^^^^^^^^^^^^^^^^ expected an implementor of trait `Clone`
+   |     |
    |     required by a bound introduced by this call
    |
 note: required because of the requirements on the impl of `Clone` for `B<C>`
@@ -41,15 +41,17 @@ note: required by a bound in `is_clone`
 LL | fn is_clone<T: Clone>(_: T) {}
    |                ^^^^^ required by this bound in `is_clone`
    = note: this error originates in the derive macro `Clone` (in Nightly builds, run with -Z macro-backtrace for more info)
+help: consider borrowing here
+   |
+LL |     is_clone(&B { a: 1, b: C });
+   |              +
 
 error[E0277]: the trait bound `D: Copy` is not satisfied
   --> $DIR/deriving-copyclone.rs:35:13
    |
 LL |     is_copy(B { a: 1, b: D });
-   |     ------- ^^^^^^^^^^^^^^^^
-   |     |       |
-   |     |       expected an implementor of trait `Copy`
-   |     |       help: consider borrowing here: `&B { a: 1, b: D }`
+   |     ------- ^^^^^^^^^^^^^^^^ expected an implementor of trait `Copy`
+   |     |
    |     required by a bound introduced by this call
    |
 note: required because of the requirements on the impl of `Copy` for `B<D>`
@@ -63,6 +65,10 @@ note: required by a bound in `is_copy`
 LL | fn is_copy<T: Copy>(_: T) {}
    |               ^^^^ required by this bound in `is_copy`
    = note: this error originates in the derive macro `Copy` (in Nightly builds, run with -Z macro-backtrace for more info)
+help: consider borrowing here
+   |
+LL |     is_copy(&B { a: 1, b: D });
+   |             +
 
 error: aborting due to 3 previous errors
 
diff --git a/src/test/ui/issues/issue-20605.stderr b/src/test/ui/issues/issue-20605.stderr
index ce3ab6b5998..5a67aead75a 100644
--- a/src/test/ui/issues/issue-20605.stderr
+++ b/src/test/ui/issues/issue-20605.stderr
@@ -2,10 +2,7 @@ error[E0277]: the size for values of type `dyn Iterator<Item = &'a mut u8>` cann
   --> $DIR/issue-20605.rs:2:17
    |
 LL |     for item in *things { *item = 0 }
-   |                 ^^^^^^^
-   |                 |
-   |                 expected an implementor of trait `IntoIterator`
-   |                 help: consider mutably borrowing here: `&mut *things`
+   |                 ^^^^^^^ expected an implementor of trait `IntoIterator`
    |
    = note: the trait bound `dyn Iterator<Item = &'a mut u8>: IntoIterator` is not satisfied
    = note: required because of the requirements on the impl of `IntoIterator` for `dyn Iterator<Item = &'a mut u8>`
@@ -14,6 +11,10 @@ note: required by `into_iter`
    |
 LL |     fn into_iter(self) -> Self::IntoIter;
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+help: consider mutably borrowing here
+   |
+LL |     for item in &mut *things { *item = 0 }
+   |                 ++++
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/suggestions/imm-ref-trait-object-literal.stderr b/src/test/ui/suggestions/imm-ref-trait-object-literal.stderr
index 71779ecb729..001af27b248 100644
--- a/src/test/ui/suggestions/imm-ref-trait-object-literal.stderr
+++ b/src/test/ui/suggestions/imm-ref-trait-object-literal.stderr
@@ -22,10 +22,8 @@ error[E0277]: the trait bound `S: Trait` is not satisfied
   --> $DIR/imm-ref-trait-object-literal.rs:13:7
    |
 LL |   foo(s);
-   |   --- ^
-   |   |   |
-   |   |   expected an implementor of trait `Trait`
-   |   |   help: consider mutably borrowing here: `&mut s`
+   |   --- ^ expected an implementor of trait `Trait`
+   |   |
    |   required by a bound introduced by this call
    |
 note: required by a bound in `foo`
@@ -33,6 +31,10 @@ note: required by a bound in `foo`
    |
 LL | fn foo<X: Trait>(_: X) {}
    |           ^^^^^ required by this bound in `foo`
+help: consider mutably borrowing here
+   |
+LL |   foo(&mut s);
+   |       ++++
 
 error: aborting due to 2 previous errors
 
diff --git a/src/test/ui/suggestions/issue-62843.stderr b/src/test/ui/suggestions/issue-62843.stderr
index 93251b2c8db..29ba39cbe10 100644
--- a/src/test/ui/suggestions/issue-62843.stderr
+++ b/src/test/ui/suggestions/issue-62843.stderr
@@ -2,14 +2,16 @@ error[E0277]: expected a `FnMut<(char,)>` closure, found `String`
   --> $DIR/issue-62843.rs:4:32
    |
 LL |     println!("{:?}", line.find(pattern));
-   |                           ---- ^^^^^^^
-   |                           |    |
-   |                           |    expected an implementor of trait `Pattern<'_>`
-   |                           |    help: consider borrowing here: `&pattern`
+   |                           ---- ^^^^^^^ expected an implementor of trait `Pattern<'_>`
+   |                           |
    |                           required by a bound introduced by this call
    |
    = note: the trait bound `String: Pattern<'_>` is not satisfied
    = note: required because of the requirements on the impl of `Pattern<'_>` for `String`
+help: consider borrowing here
+   |
+LL |     println!("{:?}", line.find(&pattern));
+   |                                +
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/suggestions/issue-84973-2.stderr b/src/test/ui/suggestions/issue-84973-2.stderr
index c1a7a2e101d..2c54ea67245 100644
--- a/src/test/ui/suggestions/issue-84973-2.stderr
+++ b/src/test/ui/suggestions/issue-84973-2.stderr
@@ -2,10 +2,8 @@ error[E0277]: the trait bound `i32: Tr` is not satisfied
   --> $DIR/issue-84973-2.rs:11:9
    |
 LL |     foo(a);
-   |     --- ^
-   |     |   |
-   |     |   expected an implementor of trait `Tr`
-   |     |   help: consider mutably borrowing here: `&mut a`
+   |     --- ^ expected an implementor of trait `Tr`
+   |     |
    |     required by a bound introduced by this call
    |
 note: required by a bound in `foo`
@@ -13,6 +11,10 @@ note: required by a bound in `foo`
    |
 LL | fn foo<T: Tr>(i: T) {}
    |           ^^ required by this bound in `foo`
+help: consider mutably borrowing here
+   |
+LL |     foo(&mut a);
+   |         ++++
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/suggestions/issue-84973-negative.stderr b/src/test/ui/suggestions/issue-84973-negative.stderr
index 14b32d8515c..1f33374eb29 100644
--- a/src/test/ui/suggestions/issue-84973-negative.stderr
+++ b/src/test/ui/suggestions/issue-84973-negative.stderr
@@ -16,10 +16,8 @@ error[E0277]: the trait bound `f32: Tr` is not satisfied
   --> $DIR/issue-84973-negative.rs:11:9
    |
 LL |     bar(b);
-   |     --- ^
-   |     |   |
-   |     |   expected an implementor of trait `Tr`
-   |     |   help: consider borrowing here: `&b`
+   |     --- ^ expected an implementor of trait `Tr`
+   |     |
    |     required by a bound introduced by this call
    |
 note: required by a bound in `bar`
@@ -27,6 +25,10 @@ note: required by a bound in `bar`
    |
 LL | fn bar<T: Tr>(t: T) {}
    |           ^^ required by this bound in `bar`
+help: consider borrowing here
+   |
+LL |     bar(&b);
+   |         +
 
 error: aborting due to 2 previous errors
 
diff --git a/src/test/ui/suggestions/issue-84973.stderr b/src/test/ui/suggestions/issue-84973.stderr
index 169d0cccb43..16a28c73aa7 100644
--- a/src/test/ui/suggestions/issue-84973.stderr
+++ b/src/test/ui/suggestions/issue-84973.stderr
@@ -2,10 +2,8 @@ error[E0277]: the trait bound `Fancy: SomeTrait` is not satisfied
   --> $DIR/issue-84973.rs:6:24
    |
 LL |     let o = Other::new(f);
-   |             ---------- ^
-   |             |          |
-   |             |          expected an implementor of trait `SomeTrait`
-   |             |          help: consider borrowing here: `&f`
+   |             ---------- ^ expected an implementor of trait `SomeTrait`
+   |             |
    |             required by a bound introduced by this call
    |
 note: required by `Other::<'a, G>::new`
@@ -13,6 +11,10 @@ note: required by `Other::<'a, G>::new`
    |
 LL |     pub fn new(g: G) -> Self {
    |     ^^^^^^^^^^^^^^^^^^^^^^^^
+help: consider borrowing here
+   |
+LL |     let o = Other::new(&f);
+   |                        +
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/suggestions/slice-issue-87994.stderr b/src/test/ui/suggestions/slice-issue-87994.stderr
index 018f62e783d..0275fd475d8 100644
--- a/src/test/ui/suggestions/slice-issue-87994.stderr
+++ b/src/test/ui/suggestions/slice-issue-87994.stderr
@@ -2,10 +2,7 @@ error[E0277]: the size for values of type `[i32]` cannot be known at compilation
   --> $DIR/slice-issue-87994.rs:3:12
    |
 LL |   for _ in v[1..] {
-   |            ^^^^^^
-   |            |
-   |            expected an implementor of trait `IntoIterator`
-   |            help: consider borrowing here: `&v[1..]`
+   |            ^^^^^^ expected an implementor of trait `IntoIterator`
    |
    = note: the trait bound `[i32]: IntoIterator` is not satisfied
    = note: required because of the requirements on the impl of `IntoIterator` for `[i32]`
@@ -14,15 +11,18 @@ note: required by `into_iter`
    |
 LL |     fn into_iter(self) -> Self::IntoIter;
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+help: consider borrowing here
+   |
+LL |   for _ in &v[1..] {
+   |            +
+LL |   for _ in &mut v[1..] {
+   |            ++++
 
 error[E0277]: `[i32]` is not an iterator
   --> $DIR/slice-issue-87994.rs:3:12
    |
 LL |   for _ in v[1..] {
-   |            ^^^^^^
-   |            |
-   |            expected an implementor of trait `IntoIterator`
-   |            help: consider borrowing here: `&v[1..]`
+   |            ^^^^^^ expected an implementor of trait `IntoIterator`
    |
    = note: the trait bound `[i32]: IntoIterator` is not satisfied
    = note: required because of the requirements on the impl of `IntoIterator` for `[i32]`
@@ -31,15 +31,18 @@ note: required by `into_iter`
    |
 LL |     fn into_iter(self) -> Self::IntoIter;
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+help: consider borrowing here
+   |
+LL |   for _ in &v[1..] {
+   |            +
+LL |   for _ in &mut v[1..] {
+   |            ++++
 
 error[E0277]: the size for values of type `[K]` cannot be known at compilation time
   --> $DIR/slice-issue-87994.rs:11:13
    |
 LL |   for i2 in v2[1..] {
-   |             ^^^^^^^
-   |             |
-   |             expected an implementor of trait `IntoIterator`
-   |             help: consider borrowing here: `&v2[1..]`
+   |             ^^^^^^^ expected an implementor of trait `IntoIterator`
    |
    = note: the trait bound `[K]: IntoIterator` is not satisfied
    = note: required because of the requirements on the impl of `IntoIterator` for `[K]`
@@ -48,15 +51,18 @@ note: required by `into_iter`
    |
 LL |     fn into_iter(self) -> Self::IntoIter;
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+help: consider borrowing here
+   |
+LL |   for i2 in &v2[1..] {
+   |             +
+LL |   for i2 in &mut v2[1..] {
+   |             ++++
 
 error[E0277]: `[K]` is not an iterator
   --> $DIR/slice-issue-87994.rs:11:13
    |
 LL |   for i2 in v2[1..] {
-   |             ^^^^^^^
-   |             |
-   |             expected an implementor of trait `IntoIterator`
-   |             help: consider borrowing here: `&v2[1..]`
+   |             ^^^^^^^ expected an implementor of trait `IntoIterator`
    |
    = note: the trait bound `[K]: IntoIterator` is not satisfied
    = note: required because of the requirements on the impl of `IntoIterator` for `[K]`
@@ -65,6 +71,12 @@ note: required by `into_iter`
    |
 LL |     fn into_iter(self) -> Self::IntoIter;
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+help: consider borrowing here
+   |
+LL |   for i2 in &v2[1..] {
+   |             +
+LL |   for i2 in &mut v2[1..] {
+   |             ++++
 
 error: aborting due to 4 previous errors
 
diff --git a/src/test/ui/suggestions/suggest-imm-mut-trait-implementations.rs b/src/test/ui/suggestions/suggest-imm-mut-trait-implementations.rs
new file mode 100644
index 00000000000..a62669d5b2d
--- /dev/null
+++ b/src/test/ui/suggestions/suggest-imm-mut-trait-implementations.rs
@@ -0,0 +1,23 @@
+trait Trait {}
+
+struct A;
+struct B;
+struct C;
+
+impl Trait for &A {}
+impl Trait for &mut A {}
+
+impl Trait for &B {}
+
+impl Trait for &mut C {}
+
+fn foo<X: Trait>(_: X) {}
+
+fn main() {
+    let a = A;
+    let b = B;
+    let c = C;
+    foo(a); //~ ERROR the trait bound `A: Trait` is not satisfied
+    foo(b); //~ ERROR the trait bound `B: Trait` is not satisfied
+    foo(c); //~ ERROR the trait bound `C: Trait` is not satisfied
+}
diff --git a/src/test/ui/suggestions/suggest-imm-mut-trait-implementations.stderr b/src/test/ui/suggestions/suggest-imm-mut-trait-implementations.stderr
new file mode 100644
index 00000000000..6583cabe184
--- /dev/null
+++ b/src/test/ui/suggestions/suggest-imm-mut-trait-implementations.stderr
@@ -0,0 +1,59 @@
+error[E0277]: the trait bound `A: Trait` is not satisfied
+  --> $DIR/suggest-imm-mut-trait-implementations.rs:20:9
+   |
+LL |     foo(a);
+   |     --- ^ expected an implementor of trait `Trait`
+   |     |
+   |     required by a bound introduced by this call
+   |
+note: required by a bound in `foo`
+  --> $DIR/suggest-imm-mut-trait-implementations.rs:14:11
+   |
+LL | fn foo<X: Trait>(_: X) {}
+   |           ^^^^^ required by this bound in `foo`
+help: consider borrowing here
+   |
+LL |     foo(&a);
+   |         +
+LL |     foo(&mut a);
+   |         ++++
+
+error[E0277]: the trait bound `B: Trait` is not satisfied
+  --> $DIR/suggest-imm-mut-trait-implementations.rs:21:9
+   |
+LL |     foo(b);
+   |     --- ^ expected an implementor of trait `Trait`
+   |     |
+   |     required by a bound introduced by this call
+   |
+note: required by a bound in `foo`
+  --> $DIR/suggest-imm-mut-trait-implementations.rs:14:11
+   |
+LL | fn foo<X: Trait>(_: X) {}
+   |           ^^^^^ required by this bound in `foo`
+help: consider borrowing here
+   |
+LL |     foo(&b);
+   |         +
+
+error[E0277]: the trait bound `C: Trait` is not satisfied
+  --> $DIR/suggest-imm-mut-trait-implementations.rs:22:9
+   |
+LL |     foo(c);
+   |     --- ^ expected an implementor of trait `Trait`
+   |     |
+   |     required by a bound introduced by this call
+   |
+note: required by a bound in `foo`
+  --> $DIR/suggest-imm-mut-trait-implementations.rs:14:11
+   |
+LL | fn foo<X: Trait>(_: X) {}
+   |           ^^^^^ required by this bound in `foo`
+help: consider mutably borrowing here
+   |
+LL |     foo(&mut c);
+   |         ++++
+
+error: aborting due to 3 previous errors
+
+For more information about this error, try `rustc --explain E0277`.
diff --git a/src/test/ui/traits/negative-impls/negated-auto-traits-error.stderr b/src/test/ui/traits/negative-impls/negated-auto-traits-error.stderr
index 790e2a81c3a..8059a8ca71e 100644
--- a/src/test/ui/traits/negative-impls/negated-auto-traits-error.stderr
+++ b/src/test/ui/traits/negative-impls/negated-auto-traits-error.stderr
@@ -61,10 +61,8 @@ error[E0277]: `dummy2::TestType` cannot be sent between threads safely
   --> $DIR/negated-auto-traits-error.rs:48:13
    |
 LL |     is_send(Box::new(TestType));
-   |     ------- ^^^^^^^^^^^^^^^^^^
-   |     |       |
-   |     |       expected an implementor of trait `Send`
-   |     |       help: consider borrowing here: `&Box::new(TestType)`
+   |     ------- ^^^^^^^^^^^^^^^^^^ expected an implementor of trait `Send`
+   |     |
    |     required by a bound introduced by this call
    |
    = note: the trait bound `dummy2::TestType: Send` is not satisfied
@@ -75,6 +73,10 @@ note: required by a bound in `is_send`
    |
 LL | fn is_send<T: Send>(_: T) {}
    |               ^^^^ required by this bound in `is_send`
+help: consider borrowing here
+   |
+LL |     is_send(&Box::new(TestType));
+   |             +
 
 error[E0277]: `dummy3::TestType` cannot be sent between threads safely
   --> $DIR/negated-auto-traits-error.rs:56:13
@@ -102,10 +104,8 @@ error[E0277]: `main::TestType` cannot be sent between threads safely
   --> $DIR/negated-auto-traits-error.rs:66:13
    |
 LL |     is_sync(Outer2(TestType));
-   |     ------- ^^^^^^^^^^^^^^^^
-   |     |       |
-   |     |       expected an implementor of trait `Sync`
-   |     |       help: consider borrowing here: `&Outer2(TestType)`
+   |     ------- ^^^^^^^^^^^^^^^^ expected an implementor of trait `Sync`
+   |     |
    |     required by a bound introduced by this call
    |
    = note: the trait bound `main::TestType: Sync` is not satisfied
@@ -119,6 +119,12 @@ note: required by a bound in `is_sync`
    |
 LL | fn is_sync<T: Sync>(_: T) {}
    |               ^^^^ required by this bound in `is_sync`
+help: consider borrowing here
+   |
+LL |     is_sync(&Outer2(TestType));
+   |             +
+LL |     is_sync(&mut Outer2(TestType));
+   |             ++++
 
 error: aborting due to 7 previous errors