Missing DefaultDllImportSearchPaths attribute in WindowsAppRuntime_EnsureIsLoaded when WindowsAppSDKSelfContained is turned on

[aries-zhang]

Describe the bug

When both WindowsAppSDKSelfContained and code analysis are turned on for a WinUI 3 project, it fails to build due to
CA5392: Use DefaultDllImportSearchPaths attribute for P/Invokes in Microsoft.Windows.Foundation.UndockedRegFreeWinRTCS.WindowsAppRuntime_EnsureIsLoaded.

Steps to reproduce the bug

1. Create a WinUI 3 project (either packaged with single project or with WAP).
2. Add <WindowsAppSDKSelfContained>true</WindowsAppSDKSelfContained> in the project file.
3. Turn on code analysis with the following project properties:

   <AnalysisMode>all</AnalysisMode>
   <AnalysisLevel>latest</AnalysisLevel>
   <CodeAnalysisTreatWarningsAsErrors>true</CodeAnalysisTreatWarningsAsErrors>
   <TreatWarningsAsErrors>true</TreatWarningsAsErrors>
   

4. Build the project.

See example code repo here: https://github.com/[aries-zhang/WinUI3-Publish-SelfContained](https://github.com/aries-zhang/WinUI3-Publish-SelfContained)

Expected behavior

1. Build should be successful.
2. No potential DLL hijacking risks should present.

Screenshots

NuGet package version

WinUI 3 - Windows App SDK 1.6.1: 1.6.240923002

Windows version

Windows 11 (24H2): Build 22621

Additional context

Since this is generated code (or included from Nuget?), it makes it hard to suppress the error individually if not a global suppression rule.

[DrusTheAxe]

This warning comes from dev\UndockedRegFreeWinRT\UndockedRegFreeWinRT-AutoInitializer.cs

[DllImport("Microsoft.WindowsAppRuntime.dll", CharSet = CharSet.Unicode, ExactSpelling = true)]
internal static extern int WindowsAppRuntime_EnsureIsLoaded();

@Scottj1s is there a value that could work in all cases? If <WindowsAppSdkUndockedRegFreeWinRTInitialize>true</> is Microsoft.WindowsAppRuntime.dll always colocated with the process' exe? Is WindowsAppSdkUndockedRegFreeWinRTInitialize=true only usable by EXEs or can be used in other cases e.g. class libraries? Would adding this attribute achieve the goal in all cases:

[DefaultDllImportSearchPaths(DllImportSearchPath.ApplicationDirectory)]

Here's the full list of possible values (bitfield, combine as desired): https://learn.microsoft.com/dotnet/api/system.runtime.interopservices.dllimportsearchpath?view=net-8.0#fields

• LegacyBehavior -- is this accurate and better than not specified?
• AssemblyDirectory
• UseDllDirectoryForDependencies
• ApplicationDirectory -- is this right in all cases?
• UserDirectories
• System32 -- shudder. Just say no
• SafeDirectories -- multiple including System32 so, no