9 files changed, 78 insertions, 16 deletions
diff --git a/tests/ui/unsized/maybe-bounds-where.rs b/tests/ui/unsized/maybe-bounds-where.rs
index d7af0c424..7e82a3eb4 100644
--- a/tests/ui/unsized/maybe-bounds-where.rs
+++ b/tests/ui/unsized/maybe-bounds-where.rs
@@ -11,11 +11,11 @@ trait Trait<'a> {}
 
 struct S4<T>(T) where for<'a> T: ?Trait<'a>;
 //~^ ERROR `?Trait` bounds are only permitted at the point where a type parameter is declared
-//~| WARN default bound relaxed for a type parameter
+//~| WARN relaxing a default bound only does something for `?Sized`
 
 struct S5<T>(*const T) where T: ?Trait<'static> + ?Sized;
 //~^ ERROR type parameter has more than one relaxed default bound
-//~| WARN default bound relaxed for a type parameter
+//~| WARN relaxing a default bound only does something for `?Sized`
 
 impl<T> S1<T> {
     fn f() where T: ?Sized {}
diff --git a/tests/ui/unsized/maybe-bounds-where.stderr b/tests/ui/unsized/maybe-bounds-where.stderr
index 39bc1b88e..683bd387b 100644
--- a/tests/ui/unsized/maybe-bounds-where.stderr
+++ b/tests/ui/unsized/maybe-bounds-where.stderr
@@ -28,23 +28,23 @@ error: `?Trait` bounds are only permitted at the point where a type parameter is
 LL |     fn f() where T: ?Sized {}
    |                     ^^^^^^
 
-warning: default bound relaxed for a type parameter, but this does nothing because the given bound is not a default; only `?Sized` is supported
-  --> $DIR/maybe-bounds-where.rs:12:11
+warning: relaxing a default bound only does something for `?Sized`; all other traits are not bound by default
+  --> $DIR/maybe-bounds-where.rs:12:34
    |
 LL | struct S4<T>(T) where for<'a> T: ?Trait<'a>;
-   |           ^
+   |                                  ^^^^^^^^^^
 
 error[E0203]: type parameter has more than one relaxed default bound, only one is supported
-  --> $DIR/maybe-bounds-where.rs:16:11
+  --> $DIR/maybe-bounds-where.rs:16:33
    |
 LL | struct S5<T>(*const T) where T: ?Trait<'static> + ?Sized;
-   |           ^
+   |                                 ^^^^^^^^^^^^^^^   ^^^^^^
 
-warning: default bound relaxed for a type parameter, but this does nothing because the given bound is not a default; only `?Sized` is supported
-  --> $DIR/maybe-bounds-where.rs:16:11
+warning: relaxing a default bound only does something for `?Sized`; all other traits are not bound by default
+  --> $DIR/maybe-bounds-where.rs:16:33
    |
 LL | struct S5<T>(*const T) where T: ?Trait<'static> + ?Sized;
-   |           ^
+   |                                 ^^^^^^^^^^^^^^^
 
 error: aborting due to 6 previous errors; 2 warnings emitted
 
diff --git a/tests/ui/unsized/unsize-coerce-multiple-adt-params.rs b/tests/ui/unsized/unsize-coerce-multiple-adt-params.rs
new file mode 100644
index 000000000..eba341ff2
--- /dev/null
+++ b/tests/ui/unsized/unsize-coerce-multiple-adt-params.rs
@@ -0,0 +1,29 @@
+// check-pass
+
+struct Foo<T, U>
+where
+    (T, U): Trait,
+{
+    f: <(T, U) as Trait>::Assoc,
+}
+
+trait Trait {
+    type Assoc: ?Sized;
+}
+
+struct Count<const N: usize>;
+
+impl<const N: usize> Trait for (i32, Count<N>) {
+    type Assoc = [(); N];
+}
+
+impl<'a> Trait for (u32, ()) {
+    type Assoc = [()];
+}
+
+// Test that we can unsize several trait params in creative ways.
+fn unsize<const N: usize>(x: &Foo<i32, Count<N>>) -> &Foo<u32, ()> {
+    x
+}
+
+fn main() {}
diff --git a/tests/ui/unsized/unsized-trait-impl-self-type.rs b/tests/ui/unsized/unsized-trait-impl-self-type.rs
index df571a833..603c0a221 100644
--- a/tests/ui/unsized/unsized-trait-impl-self-type.rs
+++ b/tests/ui/unsized/unsized-trait-impl-self-type.rs
@@ -9,6 +9,7 @@ struct S5<Y>(Y);
 
 impl<X: ?Sized> T3<X> for S5<X> {
     //~^ ERROR the size for values of type
+    //~| ERROR not all trait items implemented
 }
 
 fn main() { }
diff --git a/tests/ui/unsized/unsized-trait-impl-self-type.stderr b/tests/ui/unsized/unsized-trait-impl-self-type.stderr
index 4955d463f..5bc8dc590 100644
--- a/tests/ui/unsized/unsized-trait-impl-self-type.stderr
+++ b/tests/ui/unsized/unsized-trait-impl-self-type.stderr
@@ -24,6 +24,16 @@ LL - impl<X: ?Sized> T3<X> for S5<X> {
 LL + impl<X> T3<X> for S5<X> {
    |
 
-error: aborting due to previous error
+error[E0046]: not all trait items implemented, missing: `foo`
+  --> $DIR/unsized-trait-impl-self-type.rs:10:1
+   |
+LL |     fn foo(&self, z: &Z);
+   |     --------------------- `foo` from trait
+...
+LL | impl<X: ?Sized> T3<X> for S5<X> {
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ missing `foo` in implementation
+
+error: aborting due to 2 previous errors
 
-For more information about this error, try `rustc --explain E0277`.
+Some errors have detailed explanations: E0046, E0277.
+For more information about an error, try `rustc --explain E0046`.
diff --git a/tests/ui/unsized/unsized-trait-impl-trait-arg.rs b/tests/ui/unsized/unsized-trait-impl-trait-arg.rs
index 96e7e371f..e7602b175 100644
--- a/tests/ui/unsized/unsized-trait-impl-trait-arg.rs
+++ b/tests/ui/unsized/unsized-trait-impl-trait-arg.rs
@@ -7,6 +7,7 @@ trait T2<Z> {
 struct S4<Y: ?Sized>(Box<Y>);
 impl<X: ?Sized> T2<X> for S4<X> {
     //~^ ERROR the size for values of type
+    //~| ERROR not all trait items implemented
 }
 
 fn main() { }
diff --git a/tests/ui/unsized/unsized-trait-impl-trait-arg.stderr b/tests/ui/unsized/unsized-trait-impl-trait-arg.stderr
index 8761c293a..e9353d2bb 100644
--- a/tests/ui/unsized/unsized-trait-impl-trait-arg.stderr
+++ b/tests/ui/unsized/unsized-trait-impl-trait-arg.stderr
@@ -21,6 +21,16 @@ help: consider relaxing the implicit `Sized` restriction
 LL | trait T2<Z: ?Sized> {
    |           ++++++++
 
-error: aborting due to previous error
+error[E0046]: not all trait items implemented, missing: `foo`
+  --> $DIR/unsized-trait-impl-trait-arg.rs:8:1
+   |
+LL |     fn foo(&self, z: Z);
+   |     -------------------- `foo` from trait
+...
+LL | impl<X: ?Sized> T2<X> for S4<X> {
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ missing `foo` in implementation
+
+error: aborting due to 2 previous errors
 
-For more information about this error, try `rustc --explain E0277`.
+Some errors have detailed explanations: E0046, E0277.
+For more information about an error, try `rustc --explain E0046`.
diff --git a/tests/ui/unsized/unsized7.rs b/tests/ui/unsized/unsized7.rs
index 422a78481..63e015c28 100644
--- a/tests/ui/unsized/unsized7.rs
+++ b/tests/ui/unsized/unsized7.rs
@@ -11,6 +11,7 @@ trait T1<Z: T> {
 struct S3<Y: ?Sized>(Box<Y>);
 impl<X: ?Sized + T> T1<X> for S3<X> {
     //~^ ERROR the size for values of type
+    //~| ERROR not all trait items implemented
 }
 
 fn main() { }
diff --git a/tests/ui/unsized/unsized7.stderr b/tests/ui/unsized/unsized7.stderr
index c313a2724..2edde1596 100644
--- a/tests/ui/unsized/unsized7.stderr
+++ b/tests/ui/unsized/unsized7.stderr
@@ -21,6 +21,16 @@ help: consider relaxing the implicit `Sized` restriction
 LL | trait T1<Z: T + ?Sized> {
    |               ++++++++
 
-error: aborting due to previous error
+error[E0046]: not all trait items implemented, missing: `dummy`
+  --> $DIR/unsized7.rs:12:1
+   |
+LL |     fn dummy(&self) -> Z;
+   |     --------------------- `dummy` from trait
+...
+LL | impl<X: ?Sized + T> T1<X> for S3<X> {
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ missing `dummy` in implementation
+
+error: aborting due to 2 previous errors
 
-For more information about this error, try `rustc --explain E0277`.
+Some errors have detailed explanations: E0046, E0277.
+For more information about an error, try `rustc --explain E0046`.