Add suport for extern types.

See https://github.com/rust-lang/rust/pull/44295

src/items.rs

@@ -2740,8 +2740,10 @@ impl Rewrite for ast::ForeignItem {
                     format!("{}{}{};", prefix, sep, ty_str)
                 })
             }
-            // FIXME(#2097) support extern types.
-            ast::ForeignItemKind::Ty => unimplemented!(),
+            ast::ForeignItemKind::Ty => {
+                let vis = format_visibility(&self.vis);
+                Some(format!("{}type {};", vis, self.ident))
+            }
         }?;
 
         let missing_span = if self.attrs.is_empty() {

tests/source/extern.rs

@@ -25,6 +25,11 @@ extern {
         fn DMR_GetDevice(pHDev: *mut HDEV, searchMode: DeviceSearchMode, pSearchString: *const c_char, devNr: c_uint, wildcard: c_char) -> TDMR_ERROR;
         
     fn quux() -> (); // Post comment
+
+  pub      type
+      Foo;
+
+          type   Bar;
 }
 
 extern "Rust" { static ext:  u32;

tests/target/extern.rs

@@ -34,6 +34,10 @@ extern "C" {
     ) -> TDMR_ERROR;
 
     fn quux() -> (); // Post comment
+
+    pub type Foo;
+
+    type Bar;
 }
 
 extern "Rust" {