improve comments

tracing-attributes/src/lib.rs

@@ -650,7 +650,7 @@ fn gen_block<B: ToTokens>(
 }
 
 /// This is a more flexible/imprecise `ItemFn` type,
-/// which's block may be anything that implements `ToTokens`.
+/// which's block is just a `TokenStream` (it may contain invalid code).
 #[derive(Debug, Clone)]
 struct MaybeItemFn {
     attrs: Vec<Attribute>,
@@ -670,7 +670,7 @@ impl MaybeItemFn {
     }
 }
 
-/// This parses a TokenStream as ItemFn/MaybeItemFn but skips the body.
+/// This parses a TokenStream into a MaybeItemFn(just like ItemFn, but skips the body).
 impl Parse for MaybeItemFn {
     fn parse(input: ParseStream<'_>) -> syn::Result<Self> {
         let attrs = input.call(syn::Attribute::parse_outer)?;
@@ -686,7 +686,8 @@ impl Parse for MaybeItemFn {
     }
 }
 
-/// A generic reference type for `MaybeItemFn`.
+/// A generic reference type for `MaybeItemFn`,
+/// that takes a generic block type `B` that implements `ToTokens` (eg. `TokenStream`, `Block`).
 #[derive(Debug, Clone)]
 struct MaybeItemFnRef<'a, B: ToTokens> {
     attrs: &'a Vec<Attribute>,