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())
 }

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

@@ -46,6 +46,25 @@ pub fn generate_crate_access(unique_id: &str, def_crate: &str) -> TokenStream {
 	}
 }
 
+/// Generate the crate access for the `frame-support` crate using 2018 syntax.
+///
+/// Output will for example be `frame_support`.
+pub fn generate_crate_access_2018() -> Result<TokenStream, Error> {
+	if std::env::var("CARGO_PKG_NAME").unwrap() == "frame-support" {
+		Ok(quote::quote!( frame_support ))
+	} else {
+		match crate_name("frame-support") {
+			Ok(name) => {
+				let name = Ident::new(&name, Span::call_site());
+				Ok(quote!( #name ))
+			},
+			Err(e) => {
+				Err(Error::new(Span::call_site(), &e))
+			}
+		}
+	}
+}
+
 /// Generates the hidden includes that are required to make the macro independent from its scope.
 pub fn generate_hidden_includes(unique_id: &str, def_crate: &str) -> TokenStream {
 	if std::env::var("CARGO_PKG_NAME").unwrap() == def_crate {