[release/9.0-staging] Revert change to follow symlinks of dotnet host #116244
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#99576 changed the host to first resolve symlinks before resolving the application directory. This means that relative loads happen relative to the pointed-at file, not the symbolic link. This was a breaking change made to match the symbolic link behavior on all platforms. Unfortunately, it seems a number of users have taken a dependency on the Windows-specific behavior. This PR reverts the change and puts back in place the old Windows behavior.
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jeffschwMSFT
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Jun 3, 2025
jeffschwMSFT
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Tagging subscribers to this area: @vitek-karas, @agocke, @VSadov |
rbhanda
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/ba-g failures are timeouts that are unrelated |
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This is a revert of change #99576 and a revert of the breaking change described in https://learn.microsoft.com/en-us/dotnet/core/compatibility/deployment/9.0/assembly-load-directory
As .NET 9 has rolled out to more users, we've noticed that a number of users relied on the previous behavior of the dotnet host on Windows. The primary value in the change was to present a uniform behavior for the host around symbolic links, which hadn't previously been documented. However, users were depending on the existing symbolic-link behavior on Windows to structure their applications in reasonable scenarios. Due to the impact on users and because .NET 10 is an LTS release, I recommend we revert this change and document the differences between symlink behavior on Windows vs. Unix.
Backport of #115315 to release/9.0
/cc @agocke
Customer Impact
This has been found by multiple users, doing similar things. In both cases it was difficult to discover and potentially difficult to work around, because it involved changing deployment.
Regression
This change as introduced in .NET 9.
Testing
Unit tests have been added to verify the behavior, and specific unit tests that replicate the customer scenarios have been added. The unit tests are running on Windows, Mac, and Linux operating systems.
Risk
Medium. This may have the unfortunate result of breaking users who already adapted to the previous break. However, since .NET 10 may have even more users who discover the break, this is the preferrable option.
IMPORTANT: If this backport is for a servicing release, please verify that:
release/X.0-staging, notrelease/X.0.Package authoring no longer needed in .NET 9
IMPORTANT: Starting with .NET 9, you no longer need to edit a NuGet package's csproj to enable building and bump the version.
Keep in mind that we still need package authoring in .NET 8 and older versions.