Simplify suggestion when returning bare dyn trait

3 files changed, 17 insertions, 25 deletions

diff --git a/tests/ui/error-codes/E0746.fixed b/tests/ui/error-codes/E0746.fixed
deleted file mode 100644
index ca8319aa020..00000000000
--- a/tests/ui/error-codes/E0746.fixed
+++ /dev/null
@@ -1,18 +0,0 @@
-// run-rustfix
-#![allow(dead_code)]
-struct Struct;
-trait Trait {}
-impl Trait for Struct {}
-impl Trait for u32 {}
-
-fn foo() -> impl Trait { Struct }
-//~^ ERROR E0746
-
-fn bar() -> impl Trait { //~ ERROR E0746
-    if true {
-        return 0;
-    }
-    42
-}
-
-fn main() {}
diff --git a/tests/ui/error-codes/E0746.rs b/tests/ui/error-codes/E0746.rs
index bf5ba8fff56..86b5b7444d1 100644
--- a/tests/ui/error-codes/E0746.rs
+++ b/tests/ui/error-codes/E0746.rs
@@ -1,5 +1,5 @@
-// run-rustfix
 #![allow(dead_code)]
+
 struct Struct;
 trait Trait {}
 impl Trait for Struct {}
diff --git a/tests/ui/error-codes/E0746.stderr b/tests/ui/error-codes/E0746.stderr
index 2153b59ad18..9fe90ab7bec 100644
--- a/tests/ui/error-codes/E0746.stderr
+++ b/tests/ui/error-codes/E0746.stderr
@@ -4,11 +4,14 @@ error[E0746]: return type cannot have an unboxed trait object
 LL | fn foo() -> dyn Trait { Struct }
    |             ^^^^^^^^^ doesn't have a size known at compile-time
    |
-   = note: for information on `impl Trait`, see <https://doc.rust-lang.org/book/ch10-02-traits.html#returning-types-that-implement-traits>
-help: use `impl Trait` as the return type, as all return paths are of type `Struct`, which implements `Trait`
+help: return an `impl Trait` instead of a `dyn Trait`, if all returned values are the same type
    |
 LL | fn foo() -> impl Trait { Struct }
-   |             ~~~~~~~~~~
+   |             ~~~~
+help: box the return type, and wrap all of the returned values in `Box::new`
+   |
+LL | fn foo() -> Box<dyn Trait> { Box::new(Struct) }
+   |             ++++         +   +++++++++      +
 
 error[E0746]: return type cannot have an unboxed trait object
   --> $DIR/E0746.rs:11:13
@@ -16,11 +19,18 @@ error[E0746]: return type cannot have an unboxed trait object
 LL | fn bar() -> dyn Trait {
    |             ^^^^^^^^^ doesn't have a size known at compile-time
    |
-   = note: for information on `impl Trait`, see <https://doc.rust-lang.org/book/ch10-02-traits.html#returning-types-that-implement-traits>
-help: use `impl Trait` as the return type, as all return paths are of type `{integer}`, which implements `Trait`
+help: return an `impl Trait` instead of a `dyn Trait`, if all returned values are the same type
    |
 LL | fn bar() -> impl Trait {
-   |             ~~~~~~~~~~
+   |             ~~~~
+help: box the return type, and wrap all of the returned values in `Box::new`
+   |
+LL ~ fn bar() -> Box<dyn Trait> {
+LL |     if true {
+LL ~         return Box::new(0);
+LL |     }
+LL ~     Box::new(42)
+   |
 
 error: aborting due to 2 previous errors