[BUG] Assertion `id' failed. cpp2::using_statement_node::for_namespace

[MarekKnapek]

Steps to reproduce:

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

align_:=using"g"_:

Expected result:

• Compilation success, or nice error message printed.

Actual result:

• a.out: parse.h:2142: bool cpp2::using_statement_node::for_namespace() const: Assertion `id' failed.
• Aborted (core dumped)

Found by fuzzing, #1131.

[MarekKnapek]

Still broken in 2025, example input abc:=using"xyz", output parse.h:2181: bool cpp2::using_statement_node::for_namespace() const: Assertion `id' failed..