fix: add guard for GCC <10.3 on C++20 (#5205)

* Update CI

* update define guard

* style: pre-commit fixes

* updated define guard

* style: pre-commit fixes

* update guard

* testing new guards

* update guards

* surely this time

* style: pre-commit fixes

* Define PYBIND11_TYPING_H_HAS_STRING_LITERAL to avoid repeating a complex expression.

---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Ralf W. Grosse-Kunstleve <rwgk@google.com>

Author: 3 people

.github/workflows/ci.yml

@@ -501,7 +501,9 @@ jobs:
           - { gcc: 7, std: 17 }
           - { gcc: 8, std: 14 }
           - { gcc: 8, std: 17 }
+          - { gcc: 9, std: 20 }
           - { gcc: 10, std: 17 }
+          - { gcc: 10, std: 20 }
           - { gcc: 11, std: 20 }
           - { gcc: 12, std: 20 }
           - { gcc: 13, std: 20 }

include/pybind11/typing.h

@@ -98,7 +98,10 @@ class Never : public none {
     using none::none;
 };
 
-#if defined(__cpp_nontype_template_parameter_class)
+#if defined(__cpp_nontype_template_parameter_class)                                               \
+    && (/* See #5201 */ !defined(__GNUC__)                                                        \
+        || (__GNUC__ > 10 || (__GNUC__ == 10 && __GNUC_MINOR__ >= 3)))
+#    define PYBIND11_TYPING_H_HAS_STRING_LITERAL
 template <size_t N>
 struct StringLiteral {
     constexpr StringLiteral(const char (&str)[N]) { std::copy_n(str, N, name); }
@@ -222,7 +225,7 @@ struct handle_type_name<typing::Never> {
     static constexpr auto name = const_name("Never");
 };
 
-#if defined(__cpp_nontype_template_parameter_class)
+#if defined(PYBIND11_TYPING_H_HAS_STRING_LITERAL)
 template <typing::StringLiteral... Literals>
 struct handle_type_name<typing::Literal<Literals...>> {
     static constexpr auto name = const_name("Literal[")

tests/test_pytypes.cpp

@@ -109,7 +109,7 @@ void m_defs(py::module_ &m) {
 
 } // namespace handle_from_move_only_type_with_operator_PyObject
 
-#if defined(__cpp_nontype_template_parameter_class)
+#if defined(PYBIND11_TYPING_H_HAS_STRING_LITERAL)
 namespace literals {
 enum Color { RED = 0, BLUE = 1 };
 
@@ -905,7 +905,7 @@ TEST_SUBMODULE(pytypes, m) {
     m.def("annotate_optional_to_object",
           [](py::typing::Optional<int> &o) -> py::object { return o; });
 
-#if defined(__cpp_nontype_template_parameter_class)
+#if defined(PYBIND11_TYPING_H_HAS_STRING_LITERAL)
     py::enum_<literals::Color>(m, "Color")
         .value("RED", literals::Color::RED)
         .value("BLUE", literals::Color::BLUE);
@@ -919,8 +919,8 @@ TEST_SUBMODULE(pytypes, m) {
     m.def("annotate_listT_to_T",
           [](const py::typing::List<typevar::TypeVarT> &l) -> typevar::TypeVarT { return l[0]; });
     m.def("annotate_object_to_T", [](const py::object &o) -> typevar::TypeVarT { return o; });
-    m.attr("if_defined__cpp_nontype_template_parameter_class") = true;
+    m.attr("defined_PYBIND11_TYPING_H_HAS_STRING_LITERAL") = true;
 #else
-    m.attr("if_defined__cpp_nontype_template_parameter_class") = false;
+    m.attr("defined_PYBIND11_TYPING_H_HAS_STRING_LITERAL") = false;
 #endif
 }

tests/test_pytypes.py

@@ -1025,7 +1025,7 @@ def test_optional_object_annotations(doc):
 
 
 @pytest.mark.skipif(
-    not m.if_defined__cpp_nontype_template_parameter_class,
+    not m.defined_PYBIND11_TYPING_H_HAS_STRING_LITERAL,
     reason="C++20 feature not available.",
 )
 def test_literal(doc):
@@ -1036,7 +1036,7 @@ def test_literal(doc):
 
 
 @pytest.mark.skipif(
-    not m.if_defined__cpp_nontype_template_parameter_class,
+    not m.defined_PYBIND11_TYPING_H_HAS_STRING_LITERAL,
     reason="C++20 feature not available.",
 )
 def test_typevar(doc):