microsoft
MRTCore using MICROSOFT_WINDOWSAPPRUNTIME_BASE_DIRECTORY breaks launching one WinAppSDK app from another
Describe the bug
WinAppSDK applications which use C# registration free WinRT set the environment variable MICROSOFT_WINDOWSAPPRUNTIME_BASE_DIRECTORY.
https://github.com/microsoft/WindowsAppSDK/blob/bd8e2c16f1e15185ff31beb15cdadd550883f27e/dev/UndockedRegFreeWinRT/UndockedRegFreeWinRT-AutoInitializer.cs#L24-L27
This environment variable is used by MRTCore to locate resources.
https://github.com/microsoft/WindowsAppSDK/blob/bd8e2c16f1e15185ff31beb15cdadd550883f27e/dev/MRTCore/mrt/Core/src/MRM.cpp#L999
When that env var is present, MRTCore skips all local resource PRI locations including ModuleName.pri and just loads resources.pri out of the specified directory.
https://github.com/microsoft/WindowsAppSDK/blob/bd8e2c16f1e15185ff31beb15cdadd550883f27e/dev/MRTCore/mrt/Core/src/MRM.cpp#L1001
This explodes any application that relies on resources when it is spawned from another WinAppSDK application using CreateProcess.
A word of advice: don't use Environment Variables to communicate information across your own processes. They get inherited in places you would not expect.
Oh, and it allows a user environment variable to control where an elevated process reads a data file from. I hope that MRTCore is fuzzed. :)
@DHowett MICROSOFT_WINDOWSAPPRUNTIME_BASE_DIRECTORY is used in the implementation of PublishSingleFile, not reg-free WinRT activation. Is that your scenario? Do you see the same thing without PublishSingleFile?
(The env var was a requirement imposed upon the PublishSingleFile by fusion manifest redirection.)
@scottj1s honestly, I looked at the filename and path ("WindowsAppSDK/dev/UndockedRegFreeWinRT/UndockedRegFreeWinRT-AutoInitializer.cs") which is all about "reg" "free" and "winrt" before concluding that it had something to do with undocked reg free winrt. Perhaps my confusion is understandable. 🙂
However, I am happy to confirm that there are 300 instances of PublishSingleFile in the project where we saw this and they are all set to FALSE...