[wasi][coreclr] AppContext.BaseDirectory is "/" while assemblies are bundled under /managed

[lewing]

Description

On CoreCLR WASI, AppContext.BaseDirectory is /, but the app bundle places the app and framework assemblies under /managed:

• wasihost (src/native/corehost/wasihost/wasihost.cpp) sets TRUSTED_PLATFORM_ASSEMBLIES and APP_PATHS (the entry assembly directory, /managed/) but not APP_CONTEXT_BASE_DIRECTORY.
• CoreLib then falls back to AppContext.Browser.cs, which is shared with WASI and returns /.
• The test harness preopens the bundle directory (--dir=.) and sets CORE_ROOT=/managed.

Code that locates files next to the application therefore looks in the wrong directory. In the CoreCLR WASI library test runs on #134813:

• System.Runtime.Loader.Tests: 19 of its 22 failures are FileNotFoundException : Could not find file '/System.Reflection.Metadata.ApplyUpdate.Test...dll', and one more is the same for a System.Runtime.Loader test assembly. The tests build the path from AppContext.BaseDirectory, and the file is in /managed.
• System.Diagnostics.TraceSource.Config.Tests (8 of 8): FileNotFoundException : Could not find file '/testhost_ConfigWithRuntime.config'.

Test content deployed through WasmFilesToIncludeInFileSystem lands at the bundle root, not under managed/. So the fix has to keep both working: assemblies located through AppContext.BaseDirectory, and content opened relative to the working directory (/).

Options

1. Have wasihost set APP_CONTEXT_BASE_DIRECTORY to the entry assembly directory, as other hosts do, and deploy test content into the same directory.
2. Bundle the assemblies at the root instead of under managed/, so the base directory, working directory and assembly location coincide.

Note

This issue was drafted with the help of GitHub Copilot.

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