From 27f206f11634fa07109877e574d5c77c043b6a3a Mon Sep 17 00:00:00 2001
From: Kovid Goyal <kovid@kovidgoyal.net>
Date: Fri, 13 Jan 2023 15:40:45 +0530
Subject: [PATCH] wchar_raii now gives us a wstring_view on C++17

---
 setup/extensions.json           |  2 +-
 src/calibre/utils/cpp_binding.h | 29 ++++++++++++++++++++++++++---
 2 files changed, 27 insertions(+), 4 deletions(-)

diff --git a/setup/extensions.json b/setup/extensions.json
index b27071bf5b..6eae64d0d3 100644
--- a/setup/extensions.json
+++ b/setup/extensions.json
@@ -190,7 +190,7 @@
         "headers": "calibre/utils/cpp_binding.h calibre/utils/windows/common.h",
         "sources": "calibre/utils/windows/winspeech.cpp",
         "libraries": "WindowsApp",
-        "cflags": "/X /std:c++17 /bigobj /await /permissive- /WX /Zc:twoPhase-"
+        "cflags": "/X /std:c++17 /Zc:__cplusplus /bigobj /await /permissive- /WX /Zc:twoPhase-"
     },
     {
         "name": "wpd",
diff --git a/src/calibre/utils/cpp_binding.h b/src/calibre/utils/cpp_binding.h
index 5de1dd81d0..c27332cb81 100644
--- a/src/calibre/utils/cpp_binding.h
+++ b/src/calibre/utils/cpp_binding.h
@@ -11,6 +11,9 @@
 #define _UNICODE
 #include <Python.h>
 #include <wchar.h>
+#if __cplusplus >= 201703L
+#include <string_view>
+#endif
 
 #define arraysz(x) (sizeof(x)/sizeof(x[0]))
 
@@ -41,7 +44,23 @@ class generic_raii {
 		explicit operator bool() const noexcept { return handle != null; }
 };
 
+#if __cplusplus >= 201703L
+class wchar_raii : public generic_raii<wchar_t*, PyMem_Free> {
+    private:
+        Py_ssize_t sz;
+    public:
+        int from_unicode(PyObject *obj) {
+            wchar_t *buf = PyUnicode_AsWideCharString(obj, &sz);
+            if (!buf) return 0;
+            attach(buf);
+            return 1;
+        }
+        std::wstring_view as_view() const { return std::wstring_view(handle, sz); }
+};
+#else
 typedef generic_raii<wchar_t*, PyMem_Free> wchar_raii;
+#endif
+
 static inline void python_object_destructor(void *p) { PyObject *x = reinterpret_cast<PyObject*>(p); Py_XDECREF(x); }
 typedef generic_raii<PyObject*, python_object_destructor> pyobject_raii;
 
@@ -93,8 +112,12 @@ py_to_wchar_no_none(PyObject *obj, wchar_raii *output) {
 		PyErr_SetString(PyExc_TypeError, "unicode object expected");
 		return 0;
 	}
+#if __cplusplus >= 201703L
+    return output->from_unicode(obj);
+#else
     wchar_t *buf = PyUnicode_AsWideCharString(obj, NULL);
-    if (!buf) { PyErr_NoMemory(); return 0; }
-	output->attach(buf);
-	return 1;
+    if (!buf) { return 0; }
+    output->attach(buf);
+    return 1;
+#endif
 }