Suggest adding super trait constraints

5 files changed, 55 insertions, 9 deletions

diff --git a/src/test/ui/associated-types/defaults-unsound-62211-1.stderr b/src/test/ui/associated-types/defaults-unsound-62211-1.stderr
index 856d513d60b..c804bc3d833 100644
--- a/src/test/ui/associated-types/defaults-unsound-62211-1.stderr
+++ b/src/test/ui/associated-types/defaults-unsound-62211-1.stderr
@@ -2,7 +2,9 @@ error[E0277]: the trait bound `Self: std::marker::Copy` is not satisfied
   --> $DIR/defaults-unsound-62211-1.rs:21:18
    |
 LL | trait UncheckedCopy: Sized {
-   | -------------------------- required by `UncheckedCopy`
+   | --------------------------- help: consider further restricting `Self`: `+ std::marker::Copy`
+   | |
+   | required by `UncheckedCopy`
 ...
 LL |     type Output: Copy
    |                  ^^^^ the trait `std::marker::Copy` is not implemented for `Self`
@@ -11,7 +13,9 @@ error[E0277]: cannot add-assign `&'static str` to `Self`
   --> $DIR/defaults-unsound-62211-1.rs:25:7
    |
 LL | trait UncheckedCopy: Sized {
-   | -------------------------- required by `UncheckedCopy`
+   | --------------------------- help: consider further restricting `Self`: `+ std::ops::AddAssign<&'static str>`
+   | |
+   | required by `UncheckedCopy`
 ...
 LL |     + AddAssign<&'static str>
    |       ^^^^^^^^^^^^^^^^^^^^^^^ no implementation for `Self += &'static str`
@@ -22,7 +26,9 @@ error[E0277]: the trait bound `Self: std::ops::Deref` is not satisfied
   --> $DIR/defaults-unsound-62211-1.rs:23:7
    |
 LL | trait UncheckedCopy: Sized {
-   | -------------------------- required by `UncheckedCopy`
+   | --------------------------- help: consider further restricting `Self`: `+ std::ops::Deref`
+   | |
+   | required by `UncheckedCopy`
 ...
 LL |     + Deref<Target = str>
    |       ^^^^^^^^^^^^^^^^^^^ the trait `std::ops::Deref` is not implemented for `Self`
@@ -31,7 +37,9 @@ error[E0277]: `Self` doesn't implement `std::fmt::Display`
   --> $DIR/defaults-unsound-62211-1.rs:28:7
    |
 LL | trait UncheckedCopy: Sized {
-   | -------------------------- required by `UncheckedCopy`
+   | --------------------------- help: consider further restricting `Self`: `+ std::fmt::Display`
+   | |
+   | required by `UncheckedCopy`
 ...
 LL |     + Display = Self;
    |       ^^^^^^^ `Self` cannot be formatted with the default formatter
diff --git a/src/test/ui/associated-types/defaults-unsound-62211-2.stderr b/src/test/ui/associated-types/defaults-unsound-62211-2.stderr
index 1060c82fec2..aee5e4b28ca 100644
--- a/src/test/ui/associated-types/defaults-unsound-62211-2.stderr
+++ b/src/test/ui/associated-types/defaults-unsound-62211-2.stderr
@@ -2,7 +2,9 @@ error[E0277]: the trait bound `Self: std::marker::Copy` is not satisfied
   --> $DIR/defaults-unsound-62211-2.rs:21:18
    |
 LL | trait UncheckedCopy: Sized {
-   | -------------------------- required by `UncheckedCopy`
+   | --------------------------- help: consider further restricting `Self`: `+ std::marker::Copy`
+   | |
+   | required by `UncheckedCopy`
 ...
 LL |     type Output: Copy
    |                  ^^^^ the trait `std::marker::Copy` is not implemented for `Self`
@@ -11,7 +13,9 @@ error[E0277]: cannot add-assign `&'static str` to `Self`
   --> $DIR/defaults-unsound-62211-2.rs:25:7
    |
 LL | trait UncheckedCopy: Sized {
-   | -------------------------- required by `UncheckedCopy`
+   | --------------------------- help: consider further restricting `Self`: `+ std::ops::AddAssign<&'static str>`
+   | |
+   | required by `UncheckedCopy`
 ...
 LL |     + AddAssign<&'static str>
    |       ^^^^^^^^^^^^^^^^^^^^^^^ no implementation for `Self += &'static str`
@@ -22,7 +26,9 @@ error[E0277]: the trait bound `Self: std::ops::Deref` is not satisfied
   --> $DIR/defaults-unsound-62211-2.rs:23:7
    |
 LL | trait UncheckedCopy: Sized {
-   | -------------------------- required by `UncheckedCopy`
+   | --------------------------- help: consider further restricting `Self`: `+ std::ops::Deref`
+   | |
+   | required by `UncheckedCopy`
 ...
 LL |     + Deref<Target = str>
    |       ^^^^^^^^^^^^^^^^^^^ the trait `std::ops::Deref` is not implemented for `Self`
@@ -31,7 +37,9 @@ error[E0277]: `Self` doesn't implement `std::fmt::Display`
   --> $DIR/defaults-unsound-62211-2.rs:28:7
    |
 LL | trait UncheckedCopy: Sized {
-   | -------------------------- required by `UncheckedCopy`
+   | --------------------------- help: consider further restricting `Self`: `+ std::fmt::Display`
+   | |
+   | required by `UncheckedCopy`
 ...
 LL |     + Display = Self;
    |       ^^^^^^^ `Self` cannot be formatted with the default formatter
diff --git a/src/test/ui/associated-types/issue-63593.stderr b/src/test/ui/associated-types/issue-63593.stderr
index c27800f5a3f..42529fd2b22 100644
--- a/src/test/ui/associated-types/issue-63593.stderr
+++ b/src/test/ui/associated-types/issue-63593.stderr
@@ -2,7 +2,9 @@ error[E0277]: the size for values of type `Self` cannot be known at compilation
   --> $DIR/issue-63593.rs:9:5
    |
 LL | trait MyTrait {
-   | ------------- required by `MyTrait`
+   | -------------- help: consider further restricting `Self`: `: std::marker::Sized`
+   | |
+   | required by `MyTrait`
 LL |     type This = Self;
    |     ^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
    |
diff --git a/src/test/ui/associated-types/trait-with-supertraits-needing-sized-self.rs b/src/test/ui/associated-types/trait-with-supertraits-needing-sized-self.rs
new file mode 100644
index 00000000000..0474bf0a339
--- /dev/null
+++ b/src/test/ui/associated-types/trait-with-supertraits-needing-sized-self.rs
@@ -0,0 +1,11 @@
+use std::ops::{Add, Sub, Mul, Div};
+
+trait ArithmeticOps: Add<Output=Self> + Sub<Output=Self> + Mul<Output=Self> + Div<Output=Self> {}
+//~^ ERROR the size for values of type `Self` cannot be known at compilation time
+
+impl<T> ArithmeticOps for T where T: Add<Output=T> + Sub<Output=T> + Mul<Output=T> + Div<Output=T> {
+    // Nothing to implement, since T already supports the other traits.
+    // It has the functions it needs already
+}
+
+fn main() {}
diff --git a/src/test/ui/associated-types/trait-with-supertraits-needing-sized-self.stderr b/src/test/ui/associated-types/trait-with-supertraits-needing-sized-self.stderr
new file mode 100644
index 00000000000..707bcf5e2fe
--- /dev/null
+++ b/src/test/ui/associated-types/trait-with-supertraits-needing-sized-self.stderr
@@ -0,0 +1,17 @@
+error[E0277]: the size for values of type `Self` cannot be known at compilation time
+  --> $DIR/trait-with-supertraits-needing-sized-self.rs:3:22
+   |
+LL | trait ArithmeticOps: Add<Output=Self> + Sub<Output=Self> + Mul<Output=Self> + Div<Output=Self> {}
+   |                      ^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time               - help: consider further restricting `Self`: `+ std::marker::Sized`
+   | 
+  ::: $SRC_DIR/libcore/ops/arith.rs:LL:COL
+   |
+LL | pub trait Add<Rhs = Self> {
+   |               --- required by this bound in `std::ops::Add`
+   |
+   = help: the trait `std::marker::Sized` is not implemented for `Self`
+   = note: to learn more, visit <https://doc.rust-lang.org/book/ch19-04-advanced-types.html#dynamically-sized-types-and-the-sized-trait>
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0277`.