Upgrade to C++26 and address build errors

Author: gf712

CMakeLists.txt

@@ -5,7 +5,7 @@ include(CheckCXXSourceCompiles)
 
 project(python++)
 
-set(CMAKE_CXX_STANDARD 23)
+set(CMAKE_CXX_STANDARD 26)
 
 include(cmake/CPM.cmake)
 

src/executable/bytecode/instructions/Instructions.cpp

@@ -79,10 +79,20 @@
 
 using namespace py;
 
+// GCC 16 inlines the std::variant copy-assignment behind py::Value and then
+// attributes the std::vector destructor's operator delete to the stack slot
+// holding the variant. Nothing is freed here; the diagnostic is a false positive.
+#if defined(__GNUC__) && !defined(__clang__)
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wfree-nonheap-object"
+#endif
 Instruction::RAIIStoreNonCallInstructionData::RAIIStoreNonCallInstructionData()
 {
 	reg0 = VirtualMachine::the().reg(0);
 }
+#if defined(__GNUC__) && !defined(__clang__)
+#pragma GCC diagnostic pop
+#endif
 
 Instruction::RAIIStoreNonCallInstructionData::~RAIIStoreNonCallInstructionData()
 {

src/runtime/PyCell.cpp

@@ -80,7 +80,17 @@ bool PyCell::empty() const
 
 PyResult<PyObject *> PyCell::__repr__() const { return PyString::create(to_string()); }
 
+// GCC 16 inlines the std::variant copy-assignment behind py::Value and then
+// attributes the std::vector destructor's operator delete to the stack slot
+// holding the variant. Nothing is freed here; the diagnostic is a false positive.
+#if defined(__GNUC__) && !defined(__clang__)
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wfree-nonheap-object"
+#endif
 void PyCell::set_cell(const Value &new_value) { m_content = new_value; }
+#if defined(__GNUC__) && !defined(__clang__)
+#pragma GCC diagnostic pop
+#endif
 
 namespace {
 	std::once_flag cell_flag;

src/runtime/modules/PosixModule.cpp

@@ -17,6 +17,7 @@
 #include <string_view>
 
 #include <sys/stat.h>
+#include <unistd.h>
 
 namespace fs = std::filesystem;
 

src/runtime/modules/SysModule.cpp

@@ -40,7 +40,7 @@ PyResult<PyList *> create_sys_paths(Interpreter &interpreter)
 	const auto &entry_script = interpreter.entry_script();
 	auto entry_parent = PyString::create(std::filesystem::path(entry_script).parent_path());
 	if (entry_parent.is_err()) return Err(entry_parent.unwrap_err());
-	auto path_list = PyList::create({
+	auto path_list = PyList::create(std::vector<Value>{
 		entry_parent.unwrap(),
 		PyString::create(kPythonLibPath.data()).unwrap(),
 	});