Fix double constexpr in constructors (#55846)

Summary:
Pull Request resolved: #55846

Changelog: [Internal]

When constructors are marked as "constexpr", doxygen will output them as a function of type "constexpr" with "is-constexpr=yes". This causes the script to duplicate the keyword.

This diff fixes that by explicitly covering this edge case.

Reviewed By: cipolleschi

Differential Revision: D94901507

fbshipit-source-id: 384513381a86ba2efe07f14fd5976216ea5a8572

Author: j-piasecki

scripts/cxx-api/parser/main.py

@@ -324,6 +324,12 @@ def get_function_member(
     # Strip the trailing "=0" from the type string.
     function_type = re.sub(r"\s*=\s*0\s*$", "", function_type)
 
+    # For constexpr constructors, Doxygen outputs "constexpr" both as an
+    # attribute (constexpr="yes") and as the return type (<type>constexpr</type>).
+    # Remove the redundant type to avoid "constexpr constexpr" in output.
+    if is_constexpr and function_type == "constexpr":
+        function_type = ""
+
     doxygen_params = get_doxygen_params(function_def)
 
     function = FunctionMember(

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

@@ -0,0 +1,6 @@
+class test::Clss {
+  public constexpr Clss() = default;
+  public constexpr Clss(const test::Clss&) = default;
+  public constexpr Clss(int value);
+  public constexpr Clss(test::Clss&&) = default;
+}

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

@@ -0,0 +1,20 @@
+/*
+ * 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 {
+
+class Clss {
+ public:
+  constexpr Clss() = default;
+  constexpr Clss(const Clss &) = default;
+  constexpr Clss(Clss &&) = default;
+  explicit constexpr Clss(int value);
+};
+
+} // namespace test