Do not discard `?Sized` type params and suggest their removal

22 files changed, 462 insertions, 1 deletions

diff --git a/src/test/ui/const-generics/const-argument-if-length.full.stderr b/src/test/ui/const-generics/const-argument-if-length.full.stderr
index c6088e665a2..a9f1d0eb657 100644
--- a/src/test/ui/const-generics/const-argument-if-length.full.stderr
+++ b/src/test/ui/const-generics/const-argument-if-length.full.stderr
@@ -10,6 +10,11 @@ LL |     if std::mem::size_of::<T>() == 0 {
    |
 LL | pub const fn size_of<T>() -> usize {
    |                      - required by this bound in `std::mem::size_of`
+   |
+help: consider removing the `?Sized` bound to make the type parameter `Sized`
+   |
+LL | pub const fn is_zst<T>() -> usize {
+   |                     --
 
 error[E0277]: the size for values of type `T` cannot be known at compilation time
   --> $DIR/const-argument-if-length.rs:16:12
@@ -21,6 +26,10 @@ LL |     value: T,
    |
    = note: only the last field of a struct may have a dynamically sized type
    = help: change the field's type to have a statically known size
+help: consider removing the `?Sized` bound to make the type parameter `Sized`
+   |
+LL | pub struct AtLeastByte<T> {
+   |                        --
 help: borrowed types always have a statically known size
    |
 LL |     value: &T,
diff --git a/src/test/ui/const-generics/const-argument-if-length.min.stderr b/src/test/ui/const-generics/const-argument-if-length.min.stderr
index bc06e8d7fb1..173a1471663 100644
--- a/src/test/ui/const-generics/const-argument-if-length.min.stderr
+++ b/src/test/ui/const-generics/const-argument-if-length.min.stderr
@@ -17,6 +17,10 @@ LL |     value: T,
    |
    = note: only the last field of a struct may have a dynamically sized type
    = help: change the field's type to have a statically known size
+help: consider removing the `?Sized` bound to make the type parameter `Sized`
+   |
+LL | pub struct AtLeastByte<T> {
+   |                        --
 help: borrowed types always have a statically known size
    |
 LL |     value: &T,
diff --git a/src/test/ui/dst/dst-object-from-unsized-type.stderr b/src/test/ui/dst/dst-object-from-unsized-type.stderr
index 2d12265df98..6c57dd9316f 100644
--- a/src/test/ui/dst/dst-object-from-unsized-type.stderr
+++ b/src/test/ui/dst/dst-object-from-unsized-type.stderr
@@ -7,6 +7,10 @@ LL |     let u: &dyn Foo = t;
    |                       ^ doesn't have a size known at compile-time
    |
    = note: required for the cast to the object type `dyn Foo`
+help: consider removing the `?Sized` bound to make the type parameter `Sized`
+   |
+LL | fn test1<T: Foo>(t: &T) {
+   |            --
 
 error[E0277]: the size for values of type `T` cannot be known at compilation time
   --> $DIR/dst-object-from-unsized-type.rs:13:23
@@ -17,6 +21,10 @@ LL |     let v: &dyn Foo = t as &dyn Foo;
    |                       ^ doesn't have a size known at compile-time
    |
    = note: required for the cast to the object type `dyn Foo`
+help: consider removing the `?Sized` bound to make the type parameter `Sized`
+   |
+LL | fn test2<T: Foo>(t: &T) {
+   |            --
 
 error[E0277]: the size for values of type `str` cannot be known at compilation time
   --> $DIR/dst-object-from-unsized-type.rs:18:28
diff --git a/src/test/ui/packed/issue-27060-2.stderr b/src/test/ui/packed/issue-27060-2.stderr
index 5dbcc96e874..64e061a89b4 100644
--- a/src/test/ui/packed/issue-27060-2.stderr
+++ b/src/test/ui/packed/issue-27060-2.stderr
@@ -8,6 +8,10 @@ LL |     data: T,
    |
    = note: the last field of a packed struct may only have a dynamically sized type if it does not need drop to be run
    = help: change the field's type to have a statically known size
+help: consider removing the `?Sized` bound to make the type parameter `Sized`
+   |
+LL | pub struct Bad<T> {
+   |                --
 help: borrowed types always have a statically known size
    |
 LL |     data: &T,
diff --git a/src/test/ui/suggestions/adt-param-with-implicit-sized-bound.stderr b/src/test/ui/suggestions/adt-param-with-implicit-sized-bound.stderr
index 18ba7254446..ac3902dc6de 100644
--- a/src/test/ui/suggestions/adt-param-with-implicit-sized-bound.stderr
+++ b/src/test/ui/suggestions/adt-param-with-implicit-sized-bound.stderr
@@ -91,6 +91,10 @@ LL | struct X<T>(T);
    |          ^  - ...if indirection were used here: `Box<T>`
    |          |
    |          this could be changed to `T: ?Sized`...
+help: consider removing the `?Sized` bound to make the type parameter `Sized`
+   |
+LL | struct Struct5<T>{
+   |                --
 
 error: aborting due to 5 previous errors
 
diff --git a/src/test/ui/trait-bounds/unsized-bound.rs b/src/test/ui/trait-bounds/unsized-bound.rs
new file mode 100644
index 00000000000..035b8ef1bde
--- /dev/null
+++ b/src/test/ui/trait-bounds/unsized-bound.rs
@@ -0,0 +1,32 @@
+trait Trait<A> {}
+impl<A, B> Trait<(A, B)> for (A, B) where A: ?Sized, B: ?Sized, {}
+//~^ ERROR E0277
+//~| ERROR E0277
+impl<A, B: ?Sized, C: ?Sized> Trait<(A, B, C)> for (A, B, C) where A: ?Sized, {}
+//~^ ERROR E0277
+//~| ERROR E0277
+//~| ERROR E0277
+trait Trait2<A> {}
+impl<A: ?Sized, B: ?Sized> Trait2<(A, B)> for (A, B) {}
+//~^ ERROR E0277
+//~| ERROR E0277
+trait Trait3<A> {}
+impl<A> Trait3<A> for A where A: ?Sized {}
+//~^ ERROR E0277
+trait Trait4<A> {}
+impl<A: ?Sized> Trait4<A> for A {}
+//~^ ERROR E0277
+trait Trait5<A, B> {}
+impl<X, Y> Trait5<X, Y> for X where X: ?Sized {}
+//~^ ERROR E0277
+trait Trait6<A, B> {}
+impl<X: ?Sized, Y> Trait6<X, Y> for X {}
+//~^ ERROR E0277
+trait Trait7<A, B> {}
+impl<X, Y> Trait7<X, Y> for X where Y: ?Sized {}
+//~^ ERROR E0277
+trait Trait8<A, B> {}
+impl<X, Y: ?Sized> Trait8<X, Y> for X {}
+//~^ ERROR E0277
+
+fn main() {}
diff --git a/src/test/ui/trait-bounds/unsized-bound.stderr b/src/test/ui/trait-bounds/unsized-bound.stderr
new file mode 100644
index 00000000000..30163ab7978
--- /dev/null
+++ b/src/test/ui/trait-bounds/unsized-bound.stderr
@@ -0,0 +1,234 @@
+error[E0277]: the size for values of type `B` cannot be known at compilation time
+  --> $DIR/unsized-bound.rs:2:12
+   |
+LL | trait Trait<A> {}
+   |             - required by this bound in `Trait`
+LL | impl<A, B> Trait<(A, B)> for (A, B) where A: ?Sized, B: ?Sized, {}
+   |         -  ^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |         |
+   |         this type parameter needs to be `std::marker::Sized`
+   |
+   = note: required because it appears within the type `(A, B)`
+help: consider removing the `?Sized` bound to make the type parameter `Sized`
+   |
+LL | impl<A, B> Trait<(A, B)> for (A, B) where A: ?Sized, {}
+   |                                                   --
+help: consider relaxing the implicit `Sized` restriction
+   |
+LL | trait Trait<A: ?Sized> {}
+   |              ^^^^^^^^
+
+error[E0277]: the size for values of type `A` cannot be known at compilation time
+  --> $DIR/unsized-bound.rs:2:30
+   |
+LL | impl<A, B> Trait<(A, B)> for (A, B) where A: ?Sized, B: ?Sized, {}
+   |      -                       ^^^^^^ doesn't have a size known at compile-time
+   |      |
+   |      this type parameter needs to be `std::marker::Sized`
+   |
+   = note: only the last element of a tuple may have a dynamically sized type
+help: consider removing the `?Sized` bound to make the type parameter `Sized`
+   |
+LL | impl<A, B> Trait<(A, B)> for (A, B) where B: ?Sized, {}
+   |                                          --
+
+error[E0277]: the size for values of type `C` cannot be known at compilation time
+  --> $DIR/unsized-bound.rs:5:31
+   |
+LL | trait Trait<A> {}
+   |             - required by this bound in `Trait`
+...
+LL | impl<A, B: ?Sized, C: ?Sized> Trait<(A, B, C)> for (A, B, C) where A: ?Sized, {}
+   |                    -          ^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |                    |
+   |                    this type parameter needs to be `std::marker::Sized`
+   |
+   = note: required because it appears within the type `(A, B, C)`
+help: consider removing the `?Sized` bound to make the type parameter `Sized`
+   |
+LL | impl<A, B: ?Sized, C> Trait<(A, B, C)> for (A, B, C) where A: ?Sized, {}
+   |                    --
+help: consider relaxing the implicit `Sized` restriction
+   |
+LL | trait Trait<A: ?Sized> {}
+   |              ^^^^^^^^
+
+error[E0277]: the size for values of type `A` cannot be known at compilation time
+  --> $DIR/unsized-bound.rs:5:52
+   |
+LL | impl<A, B: ?Sized, C: ?Sized> Trait<(A, B, C)> for (A, B, C) where A: ?Sized, {}
+   |      -                                             ^^^^^^^^^ doesn't have a size known at compile-time
+   |      |
+   |      this type parameter needs to be `std::marker::Sized`
+   |
+   = note: only the last element of a tuple may have a dynamically sized type
+help: consider removing the `?Sized` bound to make the type parameter `Sized`
+   |
+LL | impl<A, B: ?Sized, C: ?Sized> Trait<(A, B, C)> for (A, B, C)  {}
+   |                                                             --
+
+error[E0277]: the size for values of type `B` cannot be known at compilation time
+  --> $DIR/unsized-bound.rs:5:52
+   |
+LL | impl<A, B: ?Sized, C: ?Sized> Trait<(A, B, C)> for (A, B, C) where A: ?Sized, {}
+   |         -                                          ^^^^^^^^^ doesn't have a size known at compile-time
+   |         |
+   |         this type parameter needs to be `std::marker::Sized`
+   |
+   = note: only the last element of a tuple may have a dynamically sized type
+help: consider removing the `?Sized` bound to make the type parameter `Sized`
+   |
+LL | impl<A, B, C: ?Sized> Trait<(A, B, C)> for (A, B, C) where A: ?Sized, {}
+   |         --
+
+error[E0277]: the size for values of type `B` cannot be known at compilation time
+  --> $DIR/unsized-bound.rs:10:28
+   |
+LL | trait Trait2<A> {}
+   |              - required by this bound in `Trait2`
+LL | impl<A: ?Sized, B: ?Sized> Trait2<(A, B)> for (A, B) {}
+   |                 -          ^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |                 |
+   |                 this type parameter needs to be `std::marker::Sized`
+   |
+   = note: required because it appears within the type `(A, B)`
+help: consider removing the `?Sized` bound to make the type parameter `Sized`
+   |
+LL | impl<A: ?Sized, B> Trait2<(A, B)> for (A, B) {}
+   |                 --
+help: consider relaxing the implicit `Sized` restriction
+   |
+LL | trait Trait2<A: ?Sized> {}
+   |               ^^^^^^^^
+
+error[E0277]: the size for values of type `A` cannot be known at compilation time
+  --> $DIR/unsized-bound.rs:10:47
+   |
+LL | impl<A: ?Sized, B: ?Sized> Trait2<(A, B)> for (A, B) {}
+   |      -                                        ^^^^^^ doesn't have a size known at compile-time
+   |      |
+   |      this type parameter needs to be `std::marker::Sized`
+   |
+   = note: only the last element of a tuple may have a dynamically sized type
+help: consider removing the `?Sized` bound to make the type parameter `Sized`
+   |
+LL | impl<A, B: ?Sized> Trait2<(A, B)> for (A, B) {}
+   |      --
+
+error[E0277]: the size for values of type `A` cannot be known at compilation time
+  --> $DIR/unsized-bound.rs:14:9
+   |
+LL | trait Trait3<A> {}
+   |              - required by this bound in `Trait3`
+LL | impl<A> Trait3<A> for A where A: ?Sized {}
+   |      -  ^^^^^^^^^ doesn't have a size known at compile-time
+   |      |
+   |      this type parameter needs to be `std::marker::Sized`
+   |
+help: consider removing the `?Sized` bound to make the type parameter `Sized`
+   |
+LL | impl<A> Trait3<A> for A  {}
+   |                        --
+help: consider relaxing the implicit `Sized` restriction
+   |
+LL | trait Trait3<A: ?Sized> {}
+   |               ^^^^^^^^
+
+error[E0277]: the size for values of type `A` cannot be known at compilation time
+  --> $DIR/unsized-bound.rs:17:17
+   |
+LL | trait Trait4<A> {}
+   |              - required by this bound in `Trait4`
+LL | impl<A: ?Sized> Trait4<A> for A {}
+   |      -          ^^^^^^^^^ doesn't have a size known at compile-time
+   |      |
+   |      this type parameter needs to be `std::marker::Sized`
+   |
+help: consider removing the `?Sized` bound to make the type parameter `Sized`
+   |
+LL | impl<A> Trait4<A> for A {}
+   |      --
+help: consider relaxing the implicit `Sized` restriction
+   |
+LL | trait Trait4<A: ?Sized> {}
+   |               ^^^^^^^^
+
+error[E0277]: the size for values of type `X` cannot be known at compilation time
+  --> $DIR/unsized-bound.rs:20:12
+   |
+LL | trait Trait5<A, B> {}
+   |              - required by this bound in `Trait5`
+LL | impl<X, Y> Trait5<X, Y> for X where X: ?Sized {}
+   |      -     ^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |      |
+   |      this type parameter needs to be `std::marker::Sized`
+   |
+help: consider removing the `?Sized` bound to make the type parameter `Sized`
+   |
+LL | impl<X, Y> Trait5<X, Y> for X  {}
+   |                              --
+help: consider relaxing the implicit `Sized` restriction
+   |
+LL | trait Trait5<A: ?Sized, B> {}
+   |               ^^^^^^^^
+
+error[E0277]: the size for values of type `X` cannot be known at compilation time
+  --> $DIR/unsized-bound.rs:23:20
+   |
+LL | trait Trait6<A, B> {}
+   |              - required by this bound in `Trait6`
+LL | impl<X: ?Sized, Y> Trait6<X, Y> for X {}
+   |      -             ^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |      |
+   |      this type parameter needs to be `std::marker::Sized`
+   |
+help: consider removing the `?Sized` bound to make the type parameter `Sized`
+   |
+LL | impl<X, Y> Trait6<X, Y> for X {}
+   |      --
+help: consider relaxing the implicit `Sized` restriction
+   |
+LL | trait Trait6<A: ?Sized, B> {}
+   |               ^^^^^^^^
+
+error[E0277]: the size for values of type `Y` cannot be known at compilation time
+  --> $DIR/unsized-bound.rs:26:12
+   |
+LL | trait Trait7<A, B> {}
+   |                 - required by this bound in `Trait7`
+LL | impl<X, Y> Trait7<X, Y> for X where Y: ?Sized {}
+   |         -  ^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |         |
+   |         this type parameter needs to be `std::marker::Sized`
+   |
+help: consider removing the `?Sized` bound to make the type parameter `Sized`
+   |
+LL | impl<X, Y> Trait7<X, Y> for X  {}
+   |                              --
+help: consider relaxing the implicit `Sized` restriction
+   |
+LL | trait Trait7<A, B: ?Sized> {}
+   |                  ^^^^^^^^
+
+error[E0277]: the size for values of type `Y` cannot be known at compilation time
+  --> $DIR/unsized-bound.rs:29:20
+   |
+LL | trait Trait8<A, B> {}
+   |                 - required by this bound in `Trait8`
+LL | impl<X, Y: ?Sized> Trait8<X, Y> for X {}
+   |         -          ^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |         |
+   |         this type parameter needs to be `std::marker::Sized`
+   |
+help: consider removing the `?Sized` bound to make the type parameter `Sized`
+   |
+LL | impl<X, Y> Trait8<X, Y> for X {}
+   |         --
+help: consider relaxing the implicit `Sized` restriction
+   |
+LL | trait Trait8<A, B: ?Sized> {}
+   |                  ^^^^^^^^
+
+error: aborting due to 13 previous errors
+
+For more information about this error, try `rustc --explain E0277`.
diff --git a/src/test/ui/traits/suggest-where-clause.stderr b/src/test/ui/traits/suggest-where-clause.stderr
index f15e7e35839..47f287807d4 100644
--- a/src/test/ui/traits/suggest-where-clause.stderr
+++ b/src/test/ui/traits/suggest-where-clause.stderr
@@ -11,6 +11,11 @@ LL |     mem::size_of::<U>();
    |
 LL | pub const fn size_of<T>() -> usize {
    |                      - required by this bound in `std::mem::size_of`
+   |
+help: consider removing the `?Sized` bound to make the type parameter `Sized`
+   |
+LL | fn check<T: Iterator, U>() {
+   |                       --
 
 error[E0277]: the size for values of type `U` cannot be known at compilation time
   --> $DIR/suggest-where-clause.rs:10:5
@@ -31,6 +36,10 @@ note: required because it appears within the type `Misc<U>`
    |
 LL | struct Misc<T:?Sized>(T);
    |        ^^^^
+help: consider removing the `?Sized` bound to make the type parameter `Sized`
+   |
+LL | fn check<T: Iterator, U>() {
+   |                       --
 
 error[E0277]: the trait bound `u64: From<T>` is not satisfied
   --> $DIR/suggest-where-clause.rs:15:5
diff --git a/src/test/ui/union/union-sized-field.stderr b/src/test/ui/union/union-sized-field.stderr
index b916bbe8ad1..ef86c624e9b 100644
--- a/src/test/ui/union/union-sized-field.stderr
+++ b/src/test/ui/union/union-sized-field.stderr
@@ -8,6 +8,10 @@ LL |     value: T,
    |
    = note: no field of a union may have a dynamically sized type
    = help: change the field's type to have a statically known size
+help: consider removing the `?Sized` bound to make the type parameter `Sized`
+   |
+LL | union Foo<T> {
+   |           --
 help: borrowed types always have a statically known size
    |
 LL |     value: &T,
@@ -27,6 +31,10 @@ LL |     value: T,
    |
    = note: only the last field of a struct may have a dynamically sized type
    = help: change the field's type to have a statically known size
+help: consider removing the `?Sized` bound to make the type parameter `Sized`
+   |
+LL | struct Foo2<T> {
+   |             --
 help: borrowed types always have a statically known size
    |
 LL |     value: &T,
@@ -46,6 +54,10 @@ LL |     Value(T),
    |
    = note: no field of an enum variant may have a dynamically sized type
    = help: change the field's type to have a statically known size
+help: consider removing the `?Sized` bound to make the type parameter `Sized`
+   |
+LL | enum Foo3<T> {
+   |           --
 help: borrowed types always have a statically known size
    |
 LL |     Value(&T),
diff --git a/src/test/ui/unsized/unsized-bare-typaram.stderr b/src/test/ui/unsized/unsized-bare-typaram.stderr
index 19978ae24ca..35bba1c103a 100644
--- a/src/test/ui/unsized/unsized-bare-typaram.stderr
+++ b/src/test/ui/unsized/unsized-bare-typaram.stderr
@@ -7,6 +7,11 @@ LL | fn foo<T: ?Sized>() { bar::<T>() }
    |        -                    ^ doesn't have a size known at compile-time
    |        |
    |        this type parameter needs to be `std::marker::Sized`
+   |
+help: consider removing the `?Sized` bound to make the type parameter `Sized`
+   |
+LL | fn foo<T>() { bar::<T>() }
+   |        --
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/unsized/unsized-enum.stderr b/src/test/ui/unsized/unsized-enum.stderr
index 601db7d1cd9..f66ce2af304 100644
--- a/src/test/ui/unsized/unsized-enum.stderr
+++ b/src/test/ui/unsized/unsized-enum.stderr
@@ -16,6 +16,10 @@ LL | enum Foo<U> { FooSome(U), FooNone }
    |          ^            - ...if indirection were used here: `Box<U>`
    |          |
    |          this could be changed to `U: ?Sized`...
+help: consider removing the `?Sized` bound to make the type parameter `Sized`
+   |
+LL | fn foo2<T>() { not_sized::<Foo<T>>() }
+   |         --
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/unsized/unsized-enum2.stderr b/src/test/ui/unsized/unsized-enum2.stderr
index 1b6c8585815..b9a03d904af 100644
--- a/src/test/ui/unsized/unsized-enum2.stderr
+++ b/src/test/ui/unsized/unsized-enum2.stderr
@@ -9,6 +9,10 @@ LL |     VA(W),
    |
    = note: no field of an enum variant may have a dynamically sized type
    = help: change the field's type to have a statically known size
+help: consider removing the `?Sized` bound to make the type parameter `Sized`
+   |
+LL | enum E<W, X: ?Sized, Y: ?Sized, Z: ?Sized> {
+   |        --
 help: borrowed types always have a statically known size
    |
 LL |     VA(&W),
@@ -29,6 +33,10 @@ LL |     VB{x: X},
    |
    = note: no field of an enum variant may have a dynamically sized type
    = help: change the field's type to have a statically known size
+help: consider removing the `?Sized` bound to make the type parameter `Sized`
+   |
+LL | enum E<W: ?Sized, X, Y: ?Sized, Z: ?Sized> {
+   |                   --
 help: borrowed types always have a statically known size
    |
 LL |     VB{x: &X},
@@ -49,6 +57,10 @@ LL |     VC(isize, Y),
    |
    = note: no field of an enum variant may have a dynamically sized type
    = help: change the field's type to have a statically known size
+help: consider removing the `?Sized` bound to make the type parameter `Sized`
+   |
+LL | enum E<W: ?Sized, X: ?Sized, Y, Z: ?Sized> {
+   |                              --
 help: borrowed types always have a statically known size
    |
 LL |     VC(isize, &Y),
@@ -69,6 +81,10 @@ LL |     VD{u: isize, x: Z},
    |
    = note: no field of an enum variant may have a dynamically sized type
    = help: change the field's type to have a statically known size
+help: consider removing the `?Sized` bound to make the type parameter `Sized`
+   |
+LL | enum E<W: ?Sized, X: ?Sized, Y: ?Sized, Z> {
+   |                                         --
 help: borrowed types always have a statically known size
    |
 LL |     VD{u: isize, x: &Z},
diff --git a/src/test/ui/unsized/unsized-fn-arg.fixed b/src/test/ui/unsized/unsized-fn-arg.fixed
index 2c686c6c2b2..fd9b159a481 100644
--- a/src/test/ui/unsized/unsized-fn-arg.fixed
+++ b/src/test/ui/unsized/unsized-fn-arg.fixed
@@ -2,5 +2,5 @@
 #![crate_type="lib"]
 #![allow(unused)]
 
-fn f<T: ?Sized>(t: &T) {}
+fn f<T>(t: &T) {}
 //~^ ERROR the size for values of type `T` cannot be known at compilation time
diff --git a/src/test/ui/unsized/unsized-fn-arg.stderr b/src/test/ui/unsized/unsized-fn-arg.stderr
index 6b802ddf542..acb8a598d2c 100644
--- a/src/test/ui/unsized/unsized-fn-arg.stderr
+++ b/src/test/ui/unsized/unsized-fn-arg.stderr
@@ -7,6 +7,10 @@ LL | fn f<T: ?Sized>(t: T) {}
    |      this type parameter needs to be `std::marker::Sized`
    |
    = help: unsized fn params are gated as an unstable feature
+help: consider removing the `?Sized` bound to make the type parameter `Sized`
+   |
+LL | fn f<T>(t: T) {}
+   |      --
 help: function arguments must have a statically known size, borrowed types always have a known size
    |
 LL | fn f<T: ?Sized>(t: &T) {}
diff --git a/src/test/ui/unsized/unsized-inherent-impl-self-type.stderr b/src/test/ui/unsized/unsized-inherent-impl-self-type.stderr
index 9d072eda4e8..99f75d8c5b3 100644
--- a/src/test/ui/unsized/unsized-inherent-impl-self-type.stderr
+++ b/src/test/ui/unsized/unsized-inherent-impl-self-type.stderr
@@ -16,6 +16,10 @@ LL | struct S5<Y>(Y);
    |           ^  - ...if indirection were used here: `Box<Y>`
    |           |
    |           this could be changed to `Y: ?Sized`...
+help: consider removing the `?Sized` bound to make the type parameter `Sized`
+   |
+LL | impl<X> S5<X> {
+   |      --
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/unsized/unsized-struct.stderr b/src/test/ui/unsized/unsized-struct.stderr
index e38375bff46..71693b8130d 100644
--- a/src/test/ui/unsized/unsized-struct.stderr
+++ b/src/test/ui/unsized/unsized-struct.stderr
@@ -16,6 +16,10 @@ LL | struct Foo<T> { data: T }
    |            ^          - ...if indirection were used here: `Box<T>`
    |            |
    |            this could be changed to `T: ?Sized`...
+help: consider removing the `?Sized` bound to make the type parameter `Sized`
+   |
+LL | fn foo2<T>() { not_sized::<Foo<T>>() }
+   |         --
 
 error[E0277]: the size for values of type `T` cannot be known at compilation time
   --> $DIR/unsized-struct.rs:13:24
@@ -33,6 +37,10 @@ note: required because it appears within the type `Bar<T>`
    |
 LL | struct Bar<T: ?Sized> { data: T }
    |        ^^^
+help: consider removing the `?Sized` bound to make the type parameter `Sized`
+   |
+LL | fn bar2<T>() { is_sized::<Bar<T>>() }
+   |         --
 
 error: aborting due to 2 previous errors
 
diff --git a/src/test/ui/unsized/unsized-trait-impl-self-type.stderr b/src/test/ui/unsized/unsized-trait-impl-self-type.stderr
index aef0d0cbb83..201dbf85d20 100644
--- a/src/test/ui/unsized/unsized-trait-impl-self-type.stderr
+++ b/src/test/ui/unsized/unsized-trait-impl-self-type.stderr
@@ -16,6 +16,10 @@ LL | struct S5<Y>(Y);
    |           ^  - ...if indirection were used here: `Box<Y>`
    |           |
    |           this could be changed to `Y: ?Sized`...
+help: consider removing the `?Sized` bound to make the type parameter `Sized`
+   |
+LL | impl<X> T3<X> for S5<X> {
+   |      --
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/unsized/unsized-trait-impl-trait-arg.stderr b/src/test/ui/unsized/unsized-trait-impl-trait-arg.stderr
index f48d4ef9f14..f8f8aa8e3e9 100644
--- a/src/test/ui/unsized/unsized-trait-impl-trait-arg.stderr
+++ b/src/test/ui/unsized/unsized-trait-impl-trait-arg.stderr
@@ -9,6 +9,10 @@ LL | impl<X: ?Sized> T2<X> for S4<X> {
    |      |
    |      this type parameter needs to be `std::marker::Sized`
    |
+help: consider removing the `?Sized` bound to make the type parameter `Sized`
+   |
+LL | impl<X> T2<X> for S4<X> {
+   |      --
 help: consider relaxing the implicit `Sized` restriction
    |
 LL | trait T2<Z: ?Sized> {
diff --git a/src/test/ui/unsized/unsized3.stderr b/src/test/ui/unsized/unsized3.stderr
index bd36008aca0..10ddfe34eac 100644
--- a/src/test/ui/unsized/unsized3.stderr
+++ b/src/test/ui/unsized/unsized3.stderr
@@ -9,6 +9,10 @@ LL |     f2::<X>(x);
 LL | fn f2<X>(x: &X) {
    |       - required by this bound in `f2`
    |
+help: consider removing the `?Sized` bound to make the type parameter `Sized`
+   |
+LL | fn f1<X>(x: &X) {
+   |       --
 help: consider relaxing the implicit `Sized` restriction
    |
 LL | fn f2<X: ?Sized>(x: &X) {
@@ -25,6 +29,10 @@ LL |     f4::<X>(x);
 LL | fn f4<X: T>(x: &X) {
    |       - required by this bound in `f4`
    |
+help: consider removing the `?Sized` bound to make the type parameter `Sized`
+   |
+LL | fn f3<X: T>(x: &X) {
+   |         --
 help: consider relaxing the implicit `Sized` restriction
    |
 LL | fn f4<X: T + ?Sized>(x: &X) {
@@ -46,6 +54,10 @@ note: required because it appears within the type `S<X>`
    |
 LL | struct S<X: ?Sized> {
    |        ^
+help: consider removing the `?Sized` bound to make the type parameter `Sized`
+   |
+LL | fn f8<X>(x1: &S<X>, x2: &S<X>) {
+   |       --
 help: consider relaxing the implicit `Sized` restriction
    |
 LL | fn f5<Y: ?Sized>(x: &Y) {}
@@ -65,6 +77,10 @@ note: required because it appears within the type `S<X>`
 LL | struct S<X: ?Sized> {
    |        ^
    = note: only the last element of a tuple may have a dynamically sized type
+help: consider removing the `?Sized` bound to make the type parameter `Sized`
+   |
+LL | fn f9<X>(x1: Box<S<X>>) {
+   |       --
 
 error[E0277]: the size for values of type `X` cannot be known at compilation time
   --> $DIR/unsized3.rs:45:9
@@ -81,6 +97,10 @@ LL | struct S<X: ?Sized> {
    |        ^
    = note: required because it appears within the type `({integer}, S<X>)`
    = note: tuples must have a statically known size to be initialized
+help: consider removing the `?Sized` bound to make the type parameter `Sized`
+   |
+LL | fn f10<X>(x1: Box<S<X>>) {
+   |        --
 
 error[E0277]: the size for values of type `X` cannot be known at compilation time
   --> $DIR/unsized3.rs:45:8
@@ -99,6 +119,10 @@ note: required because it appears within the type `S<X>`
 LL | struct S<X: ?Sized> {
    |        ^
    = note: required because it appears within the type `({integer}, S<X>)`
+help: consider removing the `?Sized` bound to make the type parameter `Sized`
+   |
+LL | fn f10<X>(x1: Box<S<X>>) {
+   |        --
 help: consider relaxing the implicit `Sized` restriction
    |
 LL | fn f5<Y: ?Sized>(x: &Y) {}
diff --git a/src/test/ui/unsized/unsized5.stderr b/src/test/ui/unsized/unsized5.stderr
index 0bfd4565529..6e5b3556429 100644
--- a/src/test/ui/unsized/unsized5.stderr
+++ b/src/test/ui/unsized/unsized5.stderr
@@ -8,6 +8,10 @@ LL |     f1: X,
    |
    = note: only the last field of a struct may have a dynamically sized type
    = help: change the field's type to have a statically known size
+help: consider removing the `?Sized` bound to make the type parameter `Sized`
+   |
+LL | struct S1<X> {
+   |           --
 help: borrowed types always have a statically known size
    |
 LL |     f1: &X,
@@ -28,6 +32,10 @@ LL |     g: X,
    |
    = note: only the last field of a struct may have a dynamically sized type
    = help: change the field's type to have a statically known size
+help: consider removing the `?Sized` bound to make the type parameter `Sized`
+   |
+LL | struct S2<X> {
+   |           --
 help: borrowed types always have a statically known size
    |
 LL |     g: &X,
@@ -83,6 +91,10 @@ LL |     V1(X, isize),
    |
    = note: no field of an enum variant may have a dynamically sized type
    = help: change the field's type to have a statically known size
+help: consider removing the `?Sized` bound to make the type parameter `Sized`
+   |
+LL | enum E<X> {
+   |        --
 help: borrowed types always have a statically known size
    |
 LL |     V1(&X, isize),
@@ -102,6 +114,10 @@ LL |     V2{f1: X, f: isize},
    |
    = note: no field of an enum variant may have a dynamically sized type
    = help: change the field's type to have a statically known size
+help: consider removing the `?Sized` bound to make the type parameter `Sized`
+   |
+LL | enum F<X> {
+   |        --
 help: borrowed types always have a statically known size
    |
 LL |     V2{f1: &X, f: isize},
diff --git a/src/test/ui/unsized/unsized6.stderr b/src/test/ui/unsized/unsized6.stderr
index 8e5734dffb1..5eff89d971f 100644
--- a/src/test/ui/unsized/unsized6.stderr
+++ b/src/test/ui/unsized/unsized6.stderr
@@ -9,6 +9,10 @@ LL |     let y: Y;
    |
    = note: all local variables must have a statically known size
    = help: unsized locals are gated as an unstable feature
+help: consider removing the `?Sized` bound to make the type parameter `Sized`
+   |
+LL | fn f1<W: ?Sized, X: ?Sized, Y, Z: ?Sized>(x: &X) {
+   |                             --
 
 error[E0277]: the size for values of type `X` cannot be known at compilation time
   --> $DIR/unsized6.rs:7:12
@@ -20,6 +24,10 @@ LL |     let _: (isize, (X, isize));
    |            ^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
    |
    = note: only the last element of a tuple may have a dynamically sized type
+help: consider removing the `?Sized` bound to make the type parameter `Sized`
+   |
+LL | fn f1<W: ?Sized, X, Y: ?Sized, Z: ?Sized>(x: &X) {
+   |                  --
 
 error[E0277]: the size for values of type `Z` cannot be known at compilation time
   --> $DIR/unsized6.rs:11:12
@@ -31,6 +39,10 @@ LL |     let y: (isize, (Z, usize));
    |            ^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
    |
    = note: only the last element of a tuple may have a dynamically sized type
+help: consider removing the `?Sized` bound to make the type parameter `Sized`
+   |
+LL | fn f1<W: ?Sized, X: ?Sized, Y: ?Sized, Z>(x: &X) {
+   |                                        --
 
 error[E0277]: the size for values of type `X` cannot be known at compilation time
   --> $DIR/unsized6.rs:15:9
@@ -42,6 +54,10 @@ LL |     let y: X;
    |
    = note: all local variables must have a statically known size
    = help: unsized locals are gated as an unstable feature
+help: consider removing the `?Sized` bound to make the type parameter `Sized`
+   |
+LL | fn f2<X, Y: ?Sized>(x: &X) {
+   |       --
 
 error[E0277]: the size for values of type `Y` cannot be known at compilation time
   --> $DIR/unsized6.rs:17:12
@@ -53,6 +69,10 @@ LL |     let y: (isize, (Y, isize));
    |            ^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
    |
    = note: only the last element of a tuple may have a dynamically sized type
+help: consider removing the `?Sized` bound to make the type parameter `Sized`
+   |
+LL | fn f2<X: ?Sized, Y>(x: &X) {
+   |                  --
 
 error[E0277]: the size for values of type `X` cannot be known at compilation time
   --> $DIR/unsized6.rs:22:9
@@ -64,6 +84,10 @@ LL |     let y: X = *x1;
    |
    = note: all local variables must have a statically known size
    = help: unsized locals are gated as an unstable feature
+help: consider removing the `?Sized` bound to make the type parameter `Sized`
+   |
+LL | fn f3<X>(x1: Box<X>, x2: Box<X>, x3: Box<X>) {
+   |       --
 
 error[E0277]: the size for values of type `X` cannot be known at compilation time
   --> $DIR/unsized6.rs:24:9
@@ -76,6 +100,10 @@ LL |     let y = *x2;
    |
    = note: all local variables must have a statically known size
    = help: unsized locals are gated as an unstable feature
+help: consider removing the `?Sized` bound to make the type parameter `Sized`
+   |
+LL | fn f3<X>(x1: Box<X>, x2: Box<X>, x3: Box<X>) {
+   |       --
 
 error[E0277]: the size for values of type `X` cannot be known at compilation time
   --> $DIR/unsized6.rs:26:10
@@ -88,6 +116,10 @@ LL |     let (y, z) = (*x3, 4);
    |
    = note: all local variables must have a statically known size
    = help: unsized locals are gated as an unstable feature
+help: consider removing the `?Sized` bound to make the type parameter `Sized`
+   |
+LL | fn f3<X>(x1: Box<X>, x2: Box<X>, x3: Box<X>) {
+   |       --
 
 error[E0277]: the size for values of type `X` cannot be known at compilation time
   --> $DIR/unsized6.rs:30:9
@@ -99,6 +131,10 @@ LL |     let y: X = *x1;
    |
    = note: all local variables must have a statically known size
    = help: unsized locals are gated as an unstable feature
+help: consider removing the `?Sized` bound to make the type parameter `Sized`
+   |
+LL | fn f4<X: T>(x1: Box<X>, x2: Box<X>, x3: Box<X>) {
+   |         --
 
 error[E0277]: the size for values of type `X` cannot be known at compilation time
   --> $DIR/unsized6.rs:32:9
@@ -111,6 +147,10 @@ LL |     let y = *x2;
    |
    = note: all local variables must have a statically known size
    = help: unsized locals are gated as an unstable feature
+help: consider removing the `?Sized` bound to make the type parameter `Sized`
+   |
+LL | fn f4<X: T>(x1: Box<X>, x2: Box<X>, x3: Box<X>) {
+   |         --
 
 error[E0277]: the size for values of type `X` cannot be known at compilation time
   --> $DIR/unsized6.rs:34:10
@@ -123,6 +163,10 @@ LL |     let (y, z) = (*x3, 4);
    |
    = note: all local variables must have a statically known size
    = help: unsized locals are gated as an unstable feature
+help: consider removing the `?Sized` bound to make the type parameter `Sized`
+   |
+LL | fn f4<X: T>(x1: Box<X>, x2: Box<X>, x3: Box<X>) {
+   |         --
 
 error[E0277]: the size for values of type `X` cannot be known at compilation time
   --> $DIR/unsized6.rs:38:18
@@ -133,6 +177,10 @@ LL | fn g1<X: ?Sized>(x: X) {}
    |       this type parameter needs to be `std::marker::Sized`
    |
    = help: unsized fn params are gated as an unstable feature
+help: consider removing the `?Sized` bound to make the type parameter `Sized`
+   |
+LL | fn g1<X>(x: X) {}
+   |       --
 help: function arguments must have a statically known size, borrowed types always have a known size
    |
 LL | fn g1<X: ?Sized>(x: &X) {}
@@ -147,6 +195,10 @@ LL | fn g2<X: ?Sized + T>(x: X) {}
    |       this type parameter needs to be `std::marker::Sized`
    |
    = help: unsized fn params are gated as an unstable feature
+help: consider removing the `?Sized` bound to make the type parameter `Sized`
+   |
+LL | fn g2<X: T>(x: X) {}
+   |         --
 help: function arguments must have a statically known size, borrowed types always have a known size
    |
 LL | fn g2<X: ?Sized + T>(x: &X) {}
diff --git a/src/test/ui/unsized/unsized7.stderr b/src/test/ui/unsized/unsized7.stderr
index 7dbddd4ed24..e0d95e21296 100644
--- a/src/test/ui/unsized/unsized7.stderr
+++ b/src/test/ui/unsized/unsized7.stderr
@@ -9,6 +9,10 @@ LL | impl<X: ?Sized + T> T1<X> for S3<X> {
    |      |
    |      this type parameter needs to be `std::marker::Sized`
    |
+help: consider removing the `?Sized` bound to make the type parameter `Sized`
+   |
+LL | impl<X: T> T1<X> for S3<X> {
+   |        --
 help: consider relaxing the implicit `Sized` restriction
    |
 LL | trait T1<Z: T + ?Sized> {