doxygen: it gets extra shitty when encountering decltype(auto).

Seriously, is the parser a box full of angry monkeys?! How is this
possible.

doxygen/dox2html5.py

@@ -1849,6 +1849,12 @@ def parse_func(state: State, element: ET.Element):
     elif func.type.startswith('constexpr'):
         func.type = func.type[10:]
         func.is_constexpr = True
+    # For some effing reason, when a constexpr function has decltype(auto)
+    # return type, Doxygen swaps the order of those two, causing the constexpr
+    # to be last. See the cpp_function_attributes test for a verification.
+    elif func.type.endswith('constexpr'):
+        func.type = func.type[:-10]
+        func.is_constexpr = True
     else:
         func.is_constexpr = False
     func.prefix = ''

doxygen/test/cpp_function_attributes/input.h

@@ -29,6 +29,22 @@ struct Foo {
      * Details.
      */
     virtual void foo() const noexcept(false) = 0;
+
+    /**
+     * @brief Random type and constexpr together
+     *
+     * This is okay.
+     */
+    constexpr Foo& bar() noexcept;
+
+    /**
+     * @brief decltype(auto) and constexpr together
+     *
+     * For some reason, due to decltype(auto), Doxygen swaps the order, causing
+     * the constexpr to be hard to detect. Don't even ask how it handles
+     * trailing return types. It's just HORRIBLE.
+     */
+    constexpr decltype(auto) baz() noexcept;
 };
 
 /** @brief Base class */