feat: allow use statements to be marked unstable (#11)

This allows the pattern of re-exporting code defined in private modules,
while still requiring the unstable feature to be enabled.

example/src/lib.rs

@@ -18,3 +18,17 @@ pub fn risky_function() {
 pub struct RiskyStruct {
  pub x: u8,
 }
+
+mod private {
+ /// This function does something really risky!
+ ///
+ /// Don't use it yet!
+ #[stability::unstable(feature = "risky-private-function")]
+ pub fn risky_private_function() {
+ unimplemented!()
+ }
+}
+
+#[allow(unused_imports)]
+#[stability::unstable(feature = "risky-private-function")]
+pub use private::risky_private_function;

src/lib.rs

@@ -122,6 +122,7 @@ pub fn unstable(args: TokenStream, input: TokenStream) -> TokenStream {
  Item::Trait(item_trait) => attributes.expand(item_trait),
  Item::Const(item_const) => attributes.expand(item_const),
  Item::Static(item_static) => attributes.expand(item_static),
+ Item::Use(item_use) => attributes.expand(item_use),
  _ => panic!("unsupported item type"),
  }
 }

src/unstable.rs

@@ -136,6 +136,7 @@ impl_has_visibility!(
  syn::ItemTrait,
  syn::ItemConst,
  syn::ItemStatic,
+ syn::ItemUse,
 );
 
 impl ItemLike for syn::ItemStruct {