[BUG] except* in async def, generators, at module level or in module-level class bodies generates C that doesn't compile (__pyx_skip_add_traceback undeclared) #8043

Describe the bug

except* (new in 3.3.0) works in a normal function, but in async def, generators, at module level and in module-level class bodies, Cython generates C that uses __pyx_skip_add_traceback without declaring it. Cython itself reports no error; the C compiler fails:

error: '__pyx_skip_add_traceback' undeclared (first use in this function); did you mean '__Pyx_AddTraceback'?

FuncDefNode.generate_function_definitions declares the variable. GeneratorBodyDefNode overrides that method without the declaration, and the module init function doesn't declare it either.

Code to reproduce the behaviour:

t.py:

async def f():
    try:
        raise ExceptionGroup("g", [ValueError()])
    except* ValueError:
        r = "caught"
    return r

cython -3 t.py -o t.c
gcc -O2 -shared -fPIC $(python3-config --includes) t.c -o t$(python3-config --extension-suffix)

cython succeeds and gcc fails with the error above. Changing async def to def (and calling it normally) compiles and works.

Expected behaviour

The module compiles, and asyncio.run(t.f()) returns "caught", the same as pure Python.

OS

Ubuntu 24.04, x86_64, gcc 13.3

Python version

3.12.3

Cython version

3.3.0 (master's Nodes.py still only declares the variable in FuncDefNode)

Additional context

Declaring the variable in GeneratorBodyDefNode the same way FuncDefNode does fixes async def, generators and async generators. This is the change I tested:

--- a/Cython/Compiler/Nodes.py
+++ b/Cython/Compiler/Nodes.py
@@ -5005,6 +5005,9 @@
 
             for cname, type in code.funcstate.all_managed_temps():
                 code.put_xdecref(cname, type)
+            if code.funcstate.has_except_star:
+                tempvardecl_code.putln(
+                    f"int {Naming.skip_add_traceback_cname} = 0;")
             code.putln("if (__Pyx_PyErr_Occurred()) {")  # we allow exit without GeneratorExit / StopIteration
             if tracing:
                 code.put_trace_exception_propagating()

except* at module level, or in a module-level class body, still fails with this change. Those cases need the same declaration in the module init function.