Improve E0046

Author: GuillaumeGomez

src/librustc_typeck/diagnostics.rs

@@ -401,10 +401,35 @@ extern "C" {
 "##,
 
 E0046: r##"
+Items are missing in a trait implementation. Erroneous code example:
+
+```
+trait Foo {
+    fn foo();
+}
+
+struct Bar;
+
+impl Foo for Bar {}
+// error: not all trait items implemented, missing: `foo`
+```
+
 When trying to make some type implement a trait `Foo`, you must, at minimum,
 provide implementations for all of `Foo`'s required methods (meaning the
 methods that do not have default implementations), as well as any required
-trait items like associated types or constants.
+trait items like associated types or constants. Example:
+
+```
+trait Foo {
+    fn foo();
+}
+
+struct Bar;
+
+impl Foo for Bar {
+    fn foo() {} // ok!
+}
+```
 "##,
 
 E0049: r##"