cleanup a few hidden imports in frame-support (#1770)

Just making a few hidden imports cleaner and hidden in docs.

---------

Co-authored-by: Keith Yeung <kungfukeith11@gmail.com>

substrate/frame/staking/reward-curve/src/lib.rs

@@ -81,11 +81,12 @@ pub fn build(input: TokenStream) -> TokenStream {
 
 	let imports = match crate_name("sp-runtime") {
 		Ok(FoundCrate::Itself) => quote!(
-			extern crate sp_runtime as _sp_runtime;
+			#[doc(hidden)]
+			pub use sp_runtime as _sp_runtime;
 		),
 		Ok(FoundCrate::Name(sp_runtime)) => {
 			let ident = syn::Ident::new(&sp_runtime, Span::call_site());
-			quote!( extern crate #ident as _sp_runtime; )
+			quote!( #[doc(hidden)] pub use #ident as _sp_runtime; )
 		},
 		Err(e) => syn::Error::new(Span::call_site(), e).to_compile_error(),
 	};

substrate/frame/support/procedural/src/construct_runtime/expand/inherent.rs

@@ -90,8 +90,7 @@ pub fn expand_outer_inherent(
 				use #scrate::inherent::{ProvideInherent, IsFatalError};
 				use #scrate::traits::{IsSubType, ExtrinsicCall};
 				use #scrate::sp_runtime::traits::Block as _;
-				use #scrate::_private::sp_inherents::Error;
-				use #scrate::__private::log;
+				use #scrate::__private::{sp_inherents::Error, log};
 
 				let mut result = #scrate::inherent::CheckInherentsResult::new();
 

substrate/frame/support/procedural/tools/src/lib.rs

@@ -99,7 +99,7 @@ pub fn generate_hidden_includes(unique_id: &str, def_crate: &str) -> TokenStream
 				quote::quote!(
 					#[doc(hidden)]
 					mod #mod_name {
-						pub extern crate #name as hidden_include;
+						pub use #name as hidden_include;
 					}
 				)
 			},

substrate/frame/support/src/lib.rs

@@ -30,6 +30,7 @@
 #![cfg_attr(not(feature = "std"), no_std)]
 
 /// Export ourself as `frame_support` to make tests happy.
+#[doc(hidden)]
 extern crate self as frame_support;
 
 /// Private exports that are being used by macros.
@@ -45,6 +46,7 @@ pub mod __private {
 	pub use serde;
 	pub use sp_core::{OpaqueMetadata, Void};
 	pub use sp_core_hashing_proc_macro;
+	pub use sp_inherents;
 	pub use sp_io::{self, storage::root as storage_root};
 	pub use sp_metadata_ir as metadata_ir;
 	#[cfg(feature = "std")]
@@ -786,12 +788,6 @@ pub use serde::{Deserialize, Serialize};
 #[cfg(not(no_std))]
 pub use macro_magic;
 
-/// Private module re-exporting items used by frame support macros.
-#[doc(hidden)]
-pub mod _private {
-	pub use sp_inherents;
-}
-
 /// Prelude to be used for pallet testing, for ease of use.
 #[cfg(feature = "std")]
 pub mod testing_prelude {