Move object safety suggestions to the end of the error

Author: estebank

compiler/rustc_infer/src/traits/error_reporting/mod.rs

@@ -83,10 +83,6 @@ pub fn report_object_safety_error(
                     messages.push(msg.clone());
                 }
             }
-            if trait_span.is_some() {
-                // Only provide the help if its a local trait, otherwise it's not actionable.
-                violation.solution(&mut err);
-            }
         }
     }
     let has_multi_span = !multi_span.is_empty();
@@ -104,5 +100,13 @@ pub fn report_object_safety_error(
          to be resolvable dynamically; for more information visit \
          <https://doc.rust-lang.org/reference/items/traits.html#object-safety>",
     );
+    if trait_span.is_some() {
+        let mut reported_violations: Vec<_> = reported_violations.into_iter().collect();
+        reported_violations.sort();
+        for violation in reported_violations {
+            // Only provide the help if its a local trait, otherwise it's not actionable.
+            violation.solution(&mut err);
+        }
+    }
     err
 }

compiler/rustc_middle/src/traits/mod.rs

@@ -730,7 +730,7 @@ pub struct ImplSourceTraitAliasData<'tcx, N> {
     pub nested: Vec<N>,
 }
 
-#[derive(Clone, Debug, PartialEq, Eq, Hash, HashStable)]
+#[derive(Clone, Debug, PartialEq, Eq, Hash, HashStable, PartialOrd, Ord)]
 pub enum ObjectSafetyViolation {
     /// `Self: Sized` declared on the trait.
     SizedSelf(SmallVec<[Span; 1]>),
@@ -879,7 +879,7 @@ impl ObjectSafetyViolation {
 }
 
 /// Reasons a method might not be object-safe.
-#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, HashStable)]
+#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, HashStable, PartialOrd, Ord)]
 pub enum MethodViolationCode {
     /// e.g., `fn foo()`
     StaticMethod(Option<(&'static str, Span)>, Span, bool /* has args */),

src/test/ui/associated-consts/associated-const-in-trait.stderr

@@ -4,14 +4,14 @@ error[E0038]: the trait `Trait` cannot be made into an object
 LL | impl dyn Trait {
    |      ^^^^^^^^^ `Trait` cannot be made into an object
    |
-   = help: consider moving `N` to another trait
 note: for a trait to be "object safe" it needs to allow building a vtable to allow the call to be resolvable dynamically; for more information visit <https://doc.rust-lang.org/reference/items/traits.html#object-safety>
   --> $DIR/associated-const-in-trait.rs:6:11
    |
 LL | trait Trait {
    |       ----- this trait cannot be made into an object...
 LL |     const N: usize;
    |           ^ ...because it contains this associated `const`
+   = help: consider moving `N` to another trait
 
 error: aborting due to previous error
 

src/test/ui/associated-item/issue-48027.stderr

@@ -21,14 +21,14 @@ error[E0038]: the trait `Bar` cannot be made into an object
 LL | impl dyn Bar {}
    |      ^^^^^^^ `Bar` cannot be made into an object
    |
-   = help: consider moving `X` to another trait
 note: for a trait to be "object safe" it needs to allow building a vtable to allow the call to be resolvable dynamically; for more information visit <https://doc.rust-lang.org/reference/items/traits.html#object-safety>
   --> $DIR/issue-48027.rs:2:11
    |
 LL | trait Bar {
    |       --- this trait cannot be made into an object...
 LL |     const X: usize;
    |           ^ ...because it contains this associated `const`
+   = help: consider moving `X` to another trait
 
 error: aborting due to 2 previous errors
 

src/test/ui/coherence/coherence-impl-trait-for-trait-object-safe.stderr

@@ -4,14 +4,14 @@ error[E0038]: the trait `NotObjectSafe` cannot be made into an object
 LL | impl NotObjectSafe for dyn NotObjectSafe { }
    |                        ^^^^^^^^^^^^^^^^^ `NotObjectSafe` cannot be made into an object
    |
-   = help: consider moving `eq` to another trait
 note: for a trait to be "object safe" it needs to allow building a vtable to allow the call to be resolvable dynamically; for more information visit <https://doc.rust-lang.org/reference/items/traits.html#object-safety>
   --> $DIR/coherence-impl-trait-for-trait-object-safe.rs:6:43
    |
 LL | trait NotObjectSafe { fn eq(&self, other: Self); }
    |       -------------                       ^^^^ ...because method `eq` references the `Self` type in this parameter
    |       |
    |       this trait cannot be made into an object...
+   = help: consider moving `eq` to another trait
 
 error: aborting due to previous error
 

src/test/ui/const-generics/generic_const_exprs/object-safety-err-ret.stderr

@@ -4,14 +4,14 @@ error[E0038]: the trait `Foo` cannot be made into an object
 LL | fn use_dyn(v: &dyn Foo) {
    |                ^^^^^^^ `Foo` cannot be made into an object
    |
-   = help: consider moving `test` to another trait
 note: for a trait to be "object safe" it needs to allow building a vtable to allow the call to be resolvable dynamically; for more information visit <https://doc.rust-lang.org/reference/items/traits.html#object-safety>
   --> $DIR/object-safety-err-ret.rs:8:23
    |
 LL | trait Foo {
    |       --- this trait cannot be made into an object...
 LL |     fn test(&self) -> [u8; bar::<Self>()];
    |                       ^^^^^^^^^^^^^^^^^^^ ...because method `test` references the `Self` type in its return type
+   = help: consider moving `test` to another trait
 
 error: aborting due to previous error
 

src/test/ui/error-codes/E0038.stderr

@@ -4,14 +4,14 @@ error[E0038]: the trait `Trait` cannot be made into an object
 LL | fn call_foo(x: Box<dyn Trait>) {
    |                    ^^^^^^^^^ `Trait` cannot be made into an object
    |
-   = help: consider moving `foo` to another trait
 note: for a trait to be "object safe" it needs to allow building a vtable to allow the call to be resolvable dynamically; for more information visit <https://doc.rust-lang.org/reference/items/traits.html#object-safety>
   --> $DIR/E0038.rs:2:22
    |
 LL | trait Trait {
    |       ----- this trait cannot be made into an object...
 LL |     fn foo(&self) -> Self;
    |                      ^^^^ ...because method `foo` references the `Self` type in its return type
+   = help: consider moving `foo` to another trait
 
 error: aborting due to previous error
 

src/test/ui/feature-gates/feature-gate-object_safe_for_dispatch.stderr

@@ -40,29 +40,29 @@ error[E0038]: the trait `NonObjectSafe3` cannot be made into an object
 LL | fn takes_non_object_safe_box(obj: Box<dyn NonObjectSafe3>) {
    |                                       ^^^^^^^^^^^^^^^^^^ `NonObjectSafe3` cannot be made into an object
    |
-   = help: consider moving `foo` to another trait
 note: for a trait to be "object safe" it needs to allow building a vtable to allow the call to be resolvable dynamically; for more information visit <https://doc.rust-lang.org/reference/items/traits.html#object-safety>
   --> $DIR/feature-gate-object_safe_for_dispatch.rs:11:8
    |
 LL | trait NonObjectSafe3 {
    |       -------------- this trait cannot be made into an object...
 LL |     fn foo<T>(&self);
    |        ^^^ ...because method `foo` has generic type parameters
+   = help: consider moving `foo` to another trait
 
 error[E0038]: the trait `NonObjectSafe4` cannot be made into an object
   --> $DIR/feature-gate-object_safe_for_dispatch.rs:31:35
    |
 LL | fn return_non_object_safe_rc() -> std::rc::Rc<dyn NonObjectSafe4> {
    |                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `NonObjectSafe4` cannot be made into an object
    |
-   = help: consider moving `foo` to another trait
 note: for a trait to be "object safe" it needs to allow building a vtable to allow the call to be resolvable dynamically; for more information visit <https://doc.rust-lang.org/reference/items/traits.html#object-safety>
   --> $DIR/feature-gate-object_safe_for_dispatch.rs:15:22
    |
 LL | trait NonObjectSafe4 {
    |       -------------- this trait cannot be made into an object...
 LL |     fn foo(&self, s: &Self);
    |                      ^^^^^ ...because method `foo` references the `Self` type in this parameter
+   = help: consider moving `foo` to another trait
 
 error[E0038]: the trait `NonObjectSafe1` cannot be made into an object
   --> $DIR/feature-gate-object_safe_for_dispatch.rs:38:16

src/test/ui/generic-associated-types/gat-in-trait-path.stderr

@@ -4,14 +4,14 @@ error[E0038]: the trait `Foo` cannot be made into an object
 LL | fn f(_arg : Box<dyn for<'a> Foo<A<'a> = &'a ()>>) {}
    |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `Foo` cannot be made into an object
    |
-   = help: consider moving `A` to another trait
 note: for a trait to be "object safe" it needs to allow building a vtable to allow the call to be resolvable dynamically; for more information visit <https://doc.rust-lang.org/reference/items/traits.html#object-safety>
   --> $DIR/gat-in-trait-path.rs:5:10
    |
 LL | trait Foo {
    |       --- this trait cannot be made into an object...
 LL |     type A<'a> where Self: 'a;
    |          ^ ...because it contains the generic associated type `A`
+   = help: consider moving `A` to another trait
 
 error: aborting due to previous error
 

src/test/ui/generic-associated-types/issue-67510-pass.stderr

@@ -4,14 +4,14 @@ error[E0038]: the trait `X` cannot be made into an object
 LL | fn _func1<'a>(_x: Box<dyn X<Y<'a>=&'a ()>>) {}
    |                       ^^^^^^^^^^^^^^^^^^^ `X` cannot be made into an object
    |
-   = help: consider moving `Y` to another trait
 note: for a trait to be "object safe" it needs to allow building a vtable to allow the call to be resolvable dynamically; for more information visit <https://doc.rust-lang.org/reference/items/traits.html#object-safety>
   --> $DIR/issue-67510-pass.rs:4:10
    |
 LL | trait X {
    |       - this trait cannot be made into an object...
 LL |     type Y<'a>;
    |          ^ ...because it contains the generic associated type `Y`
+   = help: consider moving `Y` to another trait
 
 error: aborting due to previous error