update DefaultNoBound derive macro (#12723)

fix derive for empty enums

Update derive & ui tests

clean up

Apply suggestions from code review

Co-authored-by: Bastian Köcher <git@kchr.de>

rename variable

formatting & clippy

formatting

Co-authored-by: parity-processbot <>

substrate/frame/support/src/lib.rs

@@ -621,14 +621,23 @@ pub use frame_support_procedural::DebugNoBound;
 /// # use frame_support::DefaultNoBound;
 /// # use core::default::Default;
 /// trait Config {
-/// 		type C: Default;
+/// 	type C: Default;
 /// }
 ///
 /// // Foo implements [`Default`] because `C` bounds [`Default`].
 /// // Otherwise compilation will fail with an output telling `c` doesn't implement [`Default`].
 /// #[derive(DefaultNoBound)]
 /// struct Foo<T: Config> {
-/// 		c: T::C,
+/// 	c: T::C,
+/// }
+///
+/// // Also works with enums, by specifying the default with #[default]:
+/// #[derive(DefaultNoBound)]
+/// enum Bar<T: Config> {
+/// 	// Bar will implement Default as long as all of the types within Baz also implement default.
+/// 	#[default]
+/// 	Baz(T::C),
+/// 	Quxx,
 /// }
 /// ```
 pub use frame_support_procedural::DefaultNoBound;