Make transactional attribute less scope dependent (#7112)

* Make `transactional` attribute less scope dependent

The old implementation expected that `frame-support` wasn't imported
under a different name. Besides that the pr removes some whitespaces.

* Update frame/support/procedural/src/lib.rs

Co-authored-by: Guillaume Thiolliere <gui.thiolliere@gmail.com>

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

@@ -15,9 +15,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-// tag::description[]
 //! Proc macro of Support code for the runtime.
-// end::description[]
 
 #![recursion_limit="512"]
 
@@ -296,7 +294,7 @@ pub fn construct_runtime(input: TokenStream) -> TokenStream {
 /// The return type of the annotated function must be `Result`. All changes to storage performed
 /// by the annotated function are discarded if it returns `Err`, or committed if `Ok`.
 ///
-/// #Example
+/// # Example
 ///
 /// ```nocompile
 /// #[transactional]
@@ -313,5 +311,5 @@ pub fn construct_runtime(input: TokenStream) -> TokenStream {
 /// ```
 #[proc_macro_attribute]
 pub fn transactional(attr: TokenStream, input: TokenStream) -> TokenStream {
-	transactional::transactional(attr, input)
+	transactional::transactional(attr, input).unwrap_or_else(|e| e.to_compile_error().into())
 }

substrate/frame/support/procedural/src/transactional.rs

@@ -17,15 +17,17 @@
 
 use proc_macro::TokenStream;
 use quote::quote;
-use syn::{parse_macro_input, ItemFn};
+use syn::{ItemFn, Result};
+use frame_support_procedural_tools::generate_crate_access_2018;
 
-pub fn transactional(_attr: TokenStream, input: TokenStream) -> TokenStream {
-	let ItemFn { attrs, vis, sig, block } = parse_macro_input!(input as ItemFn);
+pub fn transactional(_attr: TokenStream, input: TokenStream) -> Result<TokenStream> {
+	let ItemFn { attrs, vis, sig, block } = syn::parse(input)?;
 
+	let crate_ = generate_crate_access_2018()?;
 	let output = quote! {
 		#(#attrs)*
-        #vis #sig {
-			use frame_support::storage::{with_transaction, TransactionOutcome};
+		#vis #sig {
+			use #crate_::storage::{with_transaction, TransactionOutcome};
 			with_transaction(|| {
 				let r = #block;
 				if r.is_ok() {
@@ -34,7 +36,8 @@ pub fn transactional(_attr: TokenStream, input: TokenStream) -> TokenStream {
 					TransactionOutcome::Rollback(r)
 				}
 			})
-        }
-    };
-    output.into()
+		}
+	};
+
+	Ok(output.into())
 }