From e36971f84096e5309f8b148f21b5af22b7bf5594 Mon Sep 17 00:00:00 2001
From: Kovid Goyal <kovid@kovidgoyal.net>
Date: Fri, 23 Apr 2021 13:21:48 +0530
Subject: [PATCH] Avoid needing an extra array for RAII

---
 .../mtp/windows/content_enumeration.cpp       | 10 +++----
 .../mtp/windows/device_enumeration.cpp        |  6 ++--
 src/calibre/utils/cpp_binding.h               | 28 +++++++++++++++++++
 3 files changed, 34 insertions(+), 10 deletions(-)

diff --git a/src/calibre/devices/mtp/windows/content_enumeration.cpp b/src/calibre/devices/mtp/windows/content_enumeration.cpp
index 2907857d1a..93d94c5e9a 100644
--- a/src/calibre/devices/mtp/windows/content_enumeration.cpp
+++ b/src/calibre/devices/mtp/windows/content_enumeration.cpp
@@ -314,8 +314,6 @@ find_objects_in(CComPtr<IPortableDeviceContent> &content, CComPtr<IPortableDevic
      */
     CComPtr<IEnumPortableDeviceObjectIDs> children;
     HRESULT hr = S_OK, hr2 = S_OK;
-    PWSTR child_ids[10];
-	prop_variant pv(VT_LPWSTR);
 
     Py_BEGIN_ALLOW_THREADS;
     hr = content->EnumObjects(0, parent_id, NULL, &children);
@@ -327,13 +325,13 @@ find_objects_in(CComPtr<IPortableDeviceContent> &content, CComPtr<IPortableDevic
 
     while (hr == S_OK) {
 		DWORD fetched;
+		prop_variant pv(VT_LPWSTR);
+		generic_raii_array<wchar_t*, CoTaskMemFree, 16> child_ids;
         Py_BEGIN_ALLOW_THREADS;
-        hr = children->Next(arraysz(child_ids), child_ids, &fetched);
+        hr = children->Next((ULONG)child_ids.size(), child_ids.ptr(), &fetched);
         Py_END_ALLOW_THREADS;
         if (SUCCEEDED(hr)) {
-			com_wchar_raii cleanup[arraysz(child_ids)];
-            for(DWORD i = 0; i < fetched; i++) { cleanup[i].attach(child_ids[i]); }
-            for(DWORD i = 0; i < fetched; i++) {
+            for (DWORD i = 0; i < fetched; i++) {
                 pv.pwszVal = child_ids[i];
                 hr2 = object_ids->Add(&pv);
                 pv.pwszVal = NULL;
diff --git a/src/calibre/devices/mtp/windows/device_enumeration.cpp b/src/calibre/devices/mtp/windows/device_enumeration.cpp
index 98319a4fc4..addf854730 100644
--- a/src/calibre/devices/mtp/windows/device_enumeration.cpp
+++ b/src/calibre/devices/mtp/windows/device_enumeration.cpp
@@ -85,13 +85,11 @@ get_storage_info(IPortableDevice *device) { // {{{
 
     hr = S_OK;
     while (hr == S_OK) {
-		wchar_t* object_ids[16] = {0};
+		generic_raii_array<wchar_t*, CoTaskMemFree, 16> object_ids;
         Py_BEGIN_ALLOW_THREADS;
-        hr = objects->Next(arraysz(object_ids), object_ids, &fetched);
+        hr = objects->Next((ULONG)object_ids.size(), object_ids.ptr(), &fetched);
         Py_END_ALLOW_THREADS;
         if (SUCCEEDED(hr)) {
-			com_wchar_raii cleanup[arraysz(object_ids)];
-            for (i = 0; i < arraysz(object_ids); i++) { cleanup[i].attach(object_ids[i]); };
             for(i = 0; i < fetched; i++) {
 				CComPtr<IPortableDeviceValues> values;
                 Py_BEGIN_ALLOW_THREADS;
diff --git a/src/calibre/utils/cpp_binding.h b/src/calibre/utils/cpp_binding.h
index d8ec8c31a8..359d0e4759 100644
--- a/src/calibre/utils/cpp_binding.h
+++ b/src/calibre/utils/cpp_binding.h
@@ -45,6 +45,34 @@ typedef generic_raii<wchar_t*, PyMem_Free> wchar_raii;
 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;
 
+template<typename T, void free_T(void*), size_t sz, T null=reinterpret_cast<T>(NULL)>
+class generic_raii_array {
+	private:
+		generic_raii_array( const generic_raii_array & ) noexcept;
+		generic_raii_array & operator=( const generic_raii_array & ) noexcept ;
+
+	protected:
+		T array[sz];
+
+	public:
+		explicit generic_raii_array() noexcept : array() {}
+		~generic_raii_array() noexcept { release(); }
+
+		void release() noexcept {
+			for (size_t i = 0; i < sz; i++) {
+				if (array[i] != null) {
+					free_T(array[i]);
+					array[i] = null;
+				}
+			}
+		}
+
+		T* ptr() noexcept { return reinterpret_cast<T*>(array); }
+		size_t size() const noexcept { return sz; }
+		T operator [](size_t i) noexcept { return array[i]; }
+		const T operator[](size_t i) const noexcept { return array[i]; }
+};
+
 
 static inline int
 py_to_wchar(PyObject *obj, wchar_raii *output) {