From 773667a0e45546267bfbd8ba1f06c8202e2dfef9 Mon Sep 17 00:00:00 2001
From: da-woods <dw-git@d-woods.co.uk>
Date: Tue, 5 Dec 2023 18:18:54 +0000
Subject: [PATCH] Fix an issue trying list.index indexing in FusedNode

In some Python versions, generating the error message when .index
fails to find an index leads to a compiler crash.

Fix this by not relying on type being fully set up while generating
__str__.

Fixes #5894 and #5588
---
 Cython/Compiler/PyrexTypes.py |  7 ++++++-
 tests/run/fused_cpdef.pxd     |  4 ++++
 tests/run/fused_cpdef.pyx     | 13 +++++++++++++
 3 files changed, 23 insertions(+), 1 deletion(-)
 create mode 100644 tests/run/fused_cpdef.pxd

diff --git a/Cython/Compiler/PyrexTypes.py b/Cython/Compiler/PyrexTypes.py
index b6af4a5ab3f..1fd46754e06 100644
--- a/Cython/Compiler/PyrexTypes.py
+++ b/Cython/Compiler/PyrexTypes.py
@@ -3294,7 +3294,12 @@ def declaration_code(self, entity_code,
         if self.is_overridable:
             arg_decl_list.append("int %s" % Naming.skip_dispatch_cname)
         if self.optional_arg_count:
-            arg_decl_list.append(self.op_arg_struct.declaration_code(Naming.optional_args_cname))
+            if self.op_arg_struct:
+                arg_decl_list.append(self.op_arg_struct.declaration_code(Naming.optional_args_cname))
+            else:
+                # op_arg_struct may not be initialized at this point if this class is being used
+                # to prepare a Python error message or similar.  In this case, just omit the args.
+                assert for_display
         if self.has_varargs:
             arg_decl_list.append("...")
         arg_decl_code = ", ".join(arg_decl_list)
diff --git a/tests/run/fused_cpdef.pxd b/tests/run/fused_cpdef.pxd
new file mode 100644
index 00000000000..e4f4a600dd6
--- /dev/null
+++ b/tests/run/fused_cpdef.pxd
@@ -0,0 +1,4 @@
+cimport cython
+
+cdef class C:
+    cpdef object has_default_struct(self, cython.floating x, a=?)
diff --git a/tests/run/fused_cpdef.pyx b/tests/run/fused_cpdef.pyx
index 3979570b75c..4f569c24c3e 100644
--- a/tests/run/fused_cpdef.pyx
+++ b/tests/run/fused_cpdef.pyx
@@ -205,3 +205,16 @@ def test_defaults():
     >>> mutable_default(3,[])
     [3]
     """
+
+cdef class C:
+    cpdef object has_default_struct(self, cython.floating x, a=None):
+        return x, a
+
+# https://github.com/cython/cython/issues/5588
+# On some Python versions this was causing a compiler crash
+def test_call_has_default_struct(C c, double x):
+    """
+    >>> test_call_has_default_struct(C(), 5.)
+    (5.0, None)
+    """
+    return c.has_default_struct(x)