Document that associated constants prevent a trait from being made into an object
Fixes https://github.com/rust-lang/rust/issues/47952
Add a short mention of associated constants to E0038
}
```
+### The trait cannot contain associated constants
+
+Just like static functions, associated constants aren't stored on the method
+table. If the trait or any subtrait contain an associated constant, they cannot
+be made into an object.
+
+```compile_fail,E0038
+trait Foo {
+ const X: i32;
+}
+
+impl Foo {}
+```
+
+A simple workaround is to use a helper method instead:
+
+```
+trait Foo {
+ fn x(&self) -> i32;
+}
+```
+
### The trait cannot use `Self` as a type parameter in the supertrait listing
This is similar to the second sub-error, but subtler. It happens in situations