Fix annotation typing of Optional[tuple] (#5272)

Allow it to use a Py-tuple instead of a ctuple

Cython/Compiler/PyrexTypes.py

@@ -4467,6 +4467,9 @@ def __init__(self, cname, components):
         self.exception_check = True
         self._convert_to_py_code = None
         self._convert_from_py_code = None
+        # equivalent_type must be set now because it isn't available at import time
+        from .Builtin import tuple_type
+        self.equivalent_type = tuple_type
 
     def __str__(self):
         return "(%s)" % ", ".join(str(c) for c in self.components)

tests/run/pep526_variable_annotations.py

@@ -280,6 +280,15 @@ def test_use_typing_attributes_as_non_annotations():
     print(y1, str(y2) in allowed_optional_strings)
     print(z1, str(z2) in allowed_optional_strings)
 
+def test_optional_ctuple(x: typing.Optional[tuple[float]]):
+    """
+    Should not be a C-tuple (because these can't be optional)
+    >>> test_optional_ctuple((1.0,))
+    tuple object
+    """
+    print(cython.typeof(x) + (" object" if not cython.compiled else ""))
+
+
 try:
     import numpy.typing as npt
     import numpy as np