Windows: Additional write permissions check

src/gui/folderman.cpp

@@ -1701,9 +1701,29 @@ static QString checkPathValidityRecursive(const QString &path)
         return FolderMan::tr("The selected path is not a folder!");
     }
 
+    #ifdef Q_OS_WIN
+    if (!selFile.isWritable()) {
+        // isWritable() doesn't cover all NTFS permissions
+        // Try write
+        const auto testPath = selFile.dir().filePath("nextcloud-write-test-file.txt");
+        const auto fp = fopen(testPath.toStdWString().c_str(), "w");
+        if (!fp) {
+            return FolderMan::tr("You have no permission to write to the selected folder!");
+        }
+        fclose(fp);
+
+        // Try delete
+        const auto rc = remove(testPath.toStdWString().c_str());
+        if (rc) {
+            return FolderMan::tr("You have no permission to write to the selected folder!");
+        }
+    }
+    #else
     if (!selFile.isWritable()) {
         return FolderMan::tr("You have no permission to write to the selected folder!");
     }
+    #endif
+
     return QString();
 }