Preserve docs on aliases

Author: sbrocket

macro/src/expand.rs

@@ -659,9 +659,11 @@ fn expand_rust_function_shim_impl(
 }
 
 fn expand_type_alias(alias: &TypeAlias) -> TokenStream {
+    let doc = &alias.doc;
     let ident = &alias.ident;
     let ty = &alias.ty;
     quote! {
+        #doc
         pub type #ident = #ty;
     }
 }

syntax/mod.rs

@@ -85,6 +85,7 @@ pub enum AliasKind {
 
 pub struct TypeAlias {
     pub kind: AliasKind,
+    pub doc: Doc,
     pub type_token: Token![type],
     pub ident: Ident,
     pub eq_token: Token![=],

syntax/parse.rs

@@ -396,10 +396,11 @@ fn parse_extern_verbatim(cx: &mut Errors, tokens: &TokenStream, lang: Lang) -> R
         let eq_token: Token![=] = input.parse()?;
         let ty: RustType = input.parse()?;
         let semi_token: Token![;] = input.parse()?;
-        attrs::parse_doc(cx, &attrs);
+        let doc = attrs::parse_doc(cx, &attrs);
 
         Ok(TypeAlias {
             kind: AliasKind::OpaqueCpp,
+            doc,
             type_token,
             ident,
             eq_token,