Prevent emission of type aliases in root module for inner types

 * Emit aliases in the nearest ancestor module if the parent is not a
   module, rather than in the root module
 * If an alias would refer to itself, don't emit it (this is really a
   workaround for the fact that names are sometimes not unique enough,
   e.g. the header in #2056 produces two items called f_iterator)

Author: jbg

bindgen-tests/tests/expectations/tests/opaque-template-instantiation-namespaced.rs

@@ -500,6 +500,36 @@ impl Item {
             return false;
         }
 
+        // Skip duplicate type aliases.
+        // If this item is a type alias or resolved ref, and its ultimate target
+        // has the same canonical path and will also be generated, skip this one.
+        if let ItemKind::Type(ty) = self.kind() {
+            match ty.kind() {
+                TypeKind::Alias(target_id) |
+                TypeKind::ResolvedTypeRef(target_id) => {
+                    let direct_target = ctx.resolve_item(*target_id);
+                    // Check if the direct target has the same path and will be generated.
+                    // If so, skip generating this alias/ref because the direct target
+                    // will either be generated or skipped in favour of its target.
+                    if direct_target.id() != self.id() &&
+                        direct_target.canonical_path(ctx) ==
+                            self.canonical_path(ctx) &&
+                        ctx.codegen_items().contains(&direct_target.id())
+                    {
+                        debug!(
+                            "<Item as CodeGenerator>::process_before_codegen: Skipping duplicate alias {:?} because its direct target {:?} has the same path and will be generated",
+                            self.id(),
+                            direct_target.id()
+                        );
+                        // Mark as seen so we don't process it again if reachable through another path
+                        result.set_seen(self.id());
+                        return false;
+                    }
+                }
+                _ => {}
+            }
+        }
+
         if !ctx.codegen_items().contains(&self.id()) {
             // TODO(emilio, #453): Figure out what to do when this happens
             // legitimately, we could track the opaque stuff and disable the

bindgen/codegen/mod.rs

@@ -783,17 +783,23 @@ If you encounter an error missing from this list, please file an issue or a PR!"
         assert_ne!(item.id(), self.root_module);
         assert!(self.resolve_item_fallible(item.id()).is_none());
 
-        if let Some(ref mut parent) = self.items[item.parent_id().0] {
-            if let Some(module) = parent.as_module_mut() {
+        let mut ancestor_id = item.parent_id();
+        while let Some(ref mut ancestor_item) = self.items[ancestor_id.0] {
+            if let Some(module) = ancestor_item.as_module_mut() {
                 debug!(
-                    "add_item_to_module: adding {:?} as child of parent module {:?}",
+                    "add_item_to_module: adding {:?} as child of ancestor module {:?}",
                     item.id(),
-                    item.parent_id()
+                    ancestor_id
                 );
 
                 module.children_mut().insert(item.id());
                 return;
             }
+
+            ancestor_id = ancestor_item.parent_id();
+            if ancestor_id == ancestor_item.id() {
+                break;
+            }
         }
 
         debug!(

bindgen/ir/context.rs

@@ -1058,7 +1058,7 @@ impl Type {
                 CXType_Typedef => {
                     let inner = cursor.typedef_type().expect("Not valid Type?");
                     let inner_id =
-                        Item::from_ty_or_ref(inner, location, None, ctx);
+                        Item::from_ty_or_ref(inner, location, parent_id, ctx);
                     if inner_id == potential_id {
                         warn!(
                             "Generating opaque type instead of self-referential \