Fixing QT 6.10.1 Build Failure In MozillaVPN

Nov 29, 2025 by Alex Johnson 45 views

Encountering build failures can be a frustrating experience for developers. In this article, we'll explore a specific build failure encountered while using QT 6.10.1 to build MozillaVPN version 2.33.0. The error message indicates that the return value of bool QFile::open(FILE*, QIODeviceBase::OpenMode, QFileDevice::FileHandleFlags) is being ignored, which is flagged as an error due to the nodiscard attribute. Let's dive into the details of this issue, understand its causes, and discuss potential solutions.

Understanding the Build Failure

When you're dealing with build failures, the first step is always to carefully examine the error messages. In this case, the error occurs in the WebExtCommand::run function within the webextcommand.cpp file. The specific line causing the issue is:

stdoutFile.open(stdout, QIODeviceBase::WriteOnly);

The error message ignoring return value of ‘bool QFile::open(...)’, declared with attribute ‘nodiscard’ tells us that the open function, which returns a boolean value indicating success or failure, is not being checked. The nodiscard attribute is a C++ feature that signals to the compiler that the return value of a function should not be ignored. This is a good practice to ensure that potential errors are handled properly.

To better understand the context, let's break down the components involved:

stdoutFile: This is likely an instance of QFile, a Qt class for file I/O operations.
open(...): This is the open function of the QFile class, used to open a file.
stdout: This is the standard output stream, a common destination for program output.
QIODeviceBase::WriteOnly: This flag specifies that the file should be opened in write-only mode.

The error essentially means that the code is attempting to open the standard output as a file, but it's not verifying whether the operation was successful. This can lead to issues if the file cannot be opened for some reason, and subsequent operations on stdoutFile might fail.

Potential Causes of the Issue

Several factors could contribute to this build failure. Let's explore some potential causes:

File Permissions: The program might lack the necessary permissions to write to the standard output as a file. While writing to standard output is generally allowed, there might be specific scenarios where permissions are restricted.
Resource Limitations: The system might have limitations on the number of open files or other resources, preventing the file from being opened.
File System Issues: There could be underlying issues with the file system that prevent the file from being opened.
Qt Version Compatibility: Although the code is using Qt 6.10.1, there might be subtle compatibility issues or changes in behavior compared to earlier versions.

Solutions to Resolve the Build Failure

Now that we understand the problem and its potential causes, let's discuss some solutions to fix the build failure:

Check the Return Value: The most straightforward solution is to explicitly check the return value of the open function. This ensures that the code handles the case where the file cannot be opened.
```
if (!stdoutFile.open(stdout, QIODeviceBase::WriteOnly)) {
    // Handle the error, e.g., log an error message, return an error code
    qDebug() << 
```