Add error code explanation for E0224

src/librustc_error_codes/error_codes.rs

@@ -118,6 +118,7 @@ E0220: include_str!("./error_codes/E0220.md"),
 E0221: include_str!("./error_codes/E0221.md"),
 E0222: include_str!("./error_codes/E0222.md"),
 E0223: include_str!("./error_codes/E0223.md"),
+E0224: include_str!("./error_codes/E0224.md"),
 E0225: include_str!("./error_codes/E0225.md"),
 E0229: include_str!("./error_codes/E0229.md"),
 E0230: include_str!("./error_codes/E0230.md"),
@@ -459,7 +460,6 @@ E0745: include_str!("./error_codes/E0745.md"),
 //  E0217, // ambiguous associated type, defined in multiple supertraits
 //  E0218, // no associated type defined
 //  E0219, // associated type defined in higher-ranked supertrait
-    E0224, // at least one non-builtin train is required for an object type
     E0226, // only a single explicit lifetime bound is permitted
     E0227, // ambiguous lifetime bound, explicit lifetime bound required
     E0228, // explicit lifetime bound required

src/librustc_error_codes/error_codes/E0224.md

@@ -0,0 +1,17 @@
+This fails because you are using dynamically sized trait objects without Trait
+
+Erroneous code example:
+
+```compile_fail,E0224
+fn main() {
+    let _x: &dyn = &0;
+}
+```
+
+To solve the error please add at least one trait for `&dyn`
+
+```
+fn main() {
+    let _x: &dyn ToString = &0;
+}
+```

src/test/ui/traits/trait-alias/trait-alias-only-maybe-bound.stderr

@@ -12,3 +12,4 @@ LL | type _T1 = dyn _2;
 
 error: aborting due to 2 previous errors
 
+For more information about this error, try `rustc --explain E0224`.

src/test/ui/traits/trait-object-macro-matcher.stderr

@@ -14,4 +14,5 @@ LL |     m!(dyn Copy + Send + 'static);
 
 error: aborting due to 2 previous errors
 
-For more information about this error, try `rustc --explain E0038`.
+Some errors have detailed explanations: E0038, E0224.
+For more information about an error, try `rustc --explain E0038`.

src/test/ui/traits/trait-object-vs-lifetime-2.stderr

@@ -6,3 +6,4 @@ LL |     dyn 'static +: 'static + Copy,
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0224`.

src/test/ui/traits/trait-object-vs-lifetime.stderr

@@ -30,4 +30,5 @@ LL |     let _: S<dyn 'static +, 'static>;
 
 error: aborting due to 5 previous errors
 
-For more information about this error, try `rustc --explain E0107`.
+Some errors have detailed explanations: E0107, E0224.
+For more information about an error, try `rustc --explain E0107`.

src/test/ui/traits/wf-trait-object-only-maybe-bound.stderr

@@ -12,3 +12,4 @@ LL | type _0 = dyn ?Sized;
 
 error: aborting due to 2 previous errors
 
+For more information about this error, try `rustc --explain E0224`.