Create a persistent install log file to help root cause package upgrade issues

[OneBlue]

…

Summary of the Pull Request

This change adds logic to write various package installation loglines to C:\Windows\temp\wsl-install-log.txt, which should help us root cause #11013

PR Checklist

• Closes: Link to issue #xxx
• Communication: I've discussed this with core contributors already. If work hasn't been agreed, this work might be rejected
• Tests: Added/updated if needed and all pass
• Localization: All end user facing strings can be localized
• Dev docs: Added/updated if needed
• Documentation updated: If checked, please file a pull request on our docs repo and link it here: #xxx

Detailed Description of the Pull Request / Additional comments

Validation Steps Performed

[Copilot]

Pull Request Overview

This PR adds persistent install logging functionality to help diagnose WSL package upgrade issues by creating a log file at C:\Windows\temp\wsl-install-log.txt.

Key changes:

• Implements WriteInstallLog() function to write timestamped log entries to a persistent file
• Modifies IsUpdateNeeded() to return both update status and existing version information
• Adds logging calls throughout the MSI installation process to track upgrade operations

Reviewed Changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
src/windows/wslinstaller/exe/WslInstaller.cpp	Modified IsUpdateNeeded() to return version info and added install logging call
src/windows/wslinstall/wslinstall.def	Added new WslFinalizeInstallation export
src/windows/wslinstall/DllMain.cpp	Added logging calls to MSI installation functions and new finalize function
src/windows/common/wslutil.h	Added WriteInstallLog() function declaration
src/windows/common/wslutil.cpp	Implemented WriteInstallLog() function with file handling and mutex synchronization
msipackage/package.wix.in	Added custom action for install finalization

[Copilot]

Using c_str() on a std::string to write to a file will only write the string content without accounting for UTF-8 encoding. Since the log line contains UTF-8 formatted timestamps and potentially non-ASCII characters, this should use logLine.data() and logLine.length() to ensure proper byte handling.

Suggested change

	THROW_IF_WIN32_BOOL_FALSE(WriteFile(file.get(), logLine.c_str(), static_cast<DWORD>(logLine.size()), &bytesWritten, nullptr));
	THROW_IF_WIN32_BOOL_FALSE(WriteFile(file.get(), logLine.data(), static_cast<DWORD>(logLine.size()), &bytesWritten, nullptr));

[Copilot]

Type mismatch in format string. productCode is a std::wstring (wide string) but the format string expects a narrow string. This should either convert productCode to narrow string or use a wide string format approach.

Suggested change

	WriteInstallLog(std::format("Uninstalling MSI package: {}", productCode));
	WriteInstallLog(std::format(L"Uninstalling MSI package: {}", productCode));

[benhillis]

does std::format handle this?

[OneBlue]

It does because we made it ! We have custom std::formatters to do this for us: https://github.com/microsoft/WSL/blob/332efe1a8dfdcb3d18a2d37e195cdec014f7d43f/src/shared/inc/stringshared.h#L806C1-L807C1

[Copilot]

Type mismatch in format string. The message parameter is LPCWSTR (wide string) but std::format in this context expects a narrow string. This will cause compilation errors or incorrect output.

Suggested change

	WriteInstallLog(std::format("MSI message: {}", message));
	WriteInstallLog(std::format(L"MSI message: {}", std::wstring_view(message)));