Deduplicate base classes from Doxygen using declaration (#56218)

Summary:
Pull Request resolved: #56218

Changelog: [Internal]

When a class inherits constructors via `using Base::Base;`, Doxygen incorrectly emits duplicate `basecompoundref` entries for the same base class. This caused base classes like `ConverterBase` to appear twice in the snapshot output.

This diff deduplicates base classes by name in `get_base_classes()`.

Reviewed By: cipolleschi

Differential Revision: D98118659

fbshipit-source-id: c81f663480fda48c89e6dd625a504a78eb9d7c41

Author: j-piasecki

scripts/cxx-api/parser/builders.py

@@ -166,8 +166,14 @@ def get_base_classes(
 ) -> list:
     """
     Get the base classes of a compound object.
+
+    Deduplicates base classes by name. Doxygen can emit duplicate
+    ``basecompoundref`` entries when a class inherits constructors via
+    ``using Base::Base;`` — the using-declaration is incorrectly reported
+    as an additional base class reference.
     """
     base_classes = []
+    seen_names: set[str] = set()
     if compound_object.basecompoundref:
         for base in compound_object.basecompoundref:
             # base is a compoundRefType with:
@@ -184,6 +190,10 @@ def get_base_classes(
                 # Ignore private base classes
                 continue
 
+            if base_name in seen_names:
+                continue
+            seen_names.add(base_name)
+
             base_classes.append(
                 base_class(
                     base_name,

scripts/cxx-api/tests/snapshots/should_deduplicate_base_classes_with_using_constructor/snapshot.api

@@ -0,0 +1,12 @@
+struct test::Converter<int> : public test::ConverterBase<int> {
+  public void doSomething();
+}
+
+template <typename T>
+struct test::Converter {
+}
+
+template <typename T>
+struct test::ConverterBase {
+  public ConverterBase() = default;
+}

scripts/cxx-api/tests/snapshots/should_deduplicate_base_classes_with_using_constructor/test.h

@@ -0,0 +1,26 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+#pragma once
+
+namespace test {
+
+template <typename T>
+struct ConverterBase {
+  ConverterBase() = default;
+};
+
+template <typename T>
+struct Converter {};
+
+template <>
+struct Converter<int> : public ConverterBase<int> {
+  using ConverterBase<int>::ConverterBase;
+  void doSomething();
+};
+
+} // namespace test