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x86 host path on 64-bit Windows

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The x86 versions of .NET installers for Windows have been modified to no longer add the x86 host location (Program Files (x86)\dotnet) to the PATH environment variable on 64-bit Windows systems.

With this change, if the x86 host location was added to PATH by a prior version of .NET, the x86 versions of .NET installers and .NET updates will remove it on upgrade.

This change affects .NET Core 3.1, .NET 6, .NET 7, and future versions.

This change only affects the dotnet host. It doesn't affect 32-bit/x86 application hosts, like myapp.exe. Those hosts will continue to find the x86 runtime correctly (assuming it's installed).

Previous behavior

The x86 host location was added to PATH, even on x64/Arm64 systems. Depending on which .NET architecture installer was run first, a user's machine could have either the native (x64/Arm64) or x86 host listed first in PATH.

New behavior

Going forward, the x86 host location is only added to the PATH environment variable on x86 systems and will be removed on upgrade of .NET or Visual Studio on any x64 and arm64 systems.

Version introduced

.NET 7

Reason for change

Currently, the x86 host location is added to PATH, even on x64/Arm64 systems. Depending on which .NET architecture installer is run first, a user's machine could have either the native (x64/Arm64) or the x86 host as the first location in the PATH list. This ambiguity causes problems with the initial .NET installation and during .NET servicing events. Any of these installation scenarios can modify the order of .NET hosts in PATH, making it non-deterministic. There's a high chance of behavior regression of the .NET runtime.

This change streamlines the dotnet host experience on Windows 64-bit systems. Only 64-bit hosts will be available in the system's PATH environment variable: the x64 host on x64 systems and the Arm64 host on Arm64 systems. We removed the ambiguity in the order of dotnet hosts in PATH, and only one host will be present.

If you need the x86 host in the PATH environment variable on x64/Arm64 systems, add the host location to PATH manually.

Affected APIs

None.