[BUG] Assertion `!n.declaration->is_function()' failed.

[MarekKnapek]

Steps to reproduce:

• Get latest cppfront source code.
• Compile cppfront, g++ -std=c++20 -o cppfront cppfront.cpp.
• Run cppfront on this test file:

vz:(r:(r))z--

Expected result:

• Compilation success, or nice error message printed.

Actual result:

• cppfront: to_cpp1.h:4278: void cpp2::cppfront::emit(const cpp2::parameter_declaration_node&, bool, bool, bool): Assertion `!n.declaration->is_function()' failed.
• Aborted (core dumped)

Found by fuzzing, #1131.

[hsutter]

Thanks! Please paste the source code directly into the issue, it's better to avoid a pattern of clicking on links to zipfiles (malware potential).