Installers should be aware of multi-arch OSes and warn users as appropriate

Most OSes are becoming multi-arch, in the sense that it’s possible to run multiple different architectures on the same machine. For example:

• Windows x64 and x86 - existing problem
• Apple M1 x64 and arm64
• Windows x64 and arm64
• and so on (pending future support for platform/architecture matrix)

On all platforms, the default installers will put the location of dotnet into PATH. But if they install the second architecture, the resulting experience is confusing to the users. For example:

• Install x64 .NET 5 on Windows (C:\Program Files\dotnet is added to the PATH)
• Install x86 .NET 3.1 on Windows (C:\Program Files (x86)\dotnet is appended to the PATH) The end result is that both x64 and x86 are on PATH, but the first one wins, so running: dotnet --info Will run the x64 version and only list 5.0 as installed. Also dotnet app.dll won’t work on 3.1 app, even though it was just installed.

Installers should recognize that another architecture is already on the machine and that it’s on PATH and inform user about this behavior.

See https://github.com/dotnet/runtime/issues/3820#issuecomment-817382832 for another great example of this problem and how installer warning would help.

[rickbrew]

@joeloff To detect ARM64 from an x64 MSI you’ll likely need a custom action DLL written in native code. The Win32 API you’ll want is IsWOW64Process2. It requires Win10 v1709 (aka v10.0.16299.0) despite the docs saying v1511. If the OS is pre-1709, and it says it’s x64, then you’re on x64 for real. Otherwise query that API.

NETCoreCheck provides a custom actions DLL for detecting .NET 5/6 from an MSI, so you might be able use that as a template for building your own CA DLL. https://github.com/dotnet/deployment-tools/tree/main/src/clickonce/native/projects/NetCoreCheck/CA

edit: Here’s my code that I’m using in Paint.NET as part of my setup chainer, adapt as you see fit https://gist.github.com/rickbrew/aec72f8b430375b663c1e690a5dfc01c

[richlander]

There are two aspects of this:

• How do we handle the PATH for multiple .NET architectures on a machine?
• How do we handle .NET versions that are not available/legal for a given architecture?

Here is my proposal:

• No longer automatically add the non-native .NET install directory to the PATH.
• Teach the muxer to see all .NET installs (installed to the normal location) on the machine for the purpose of good error messages.
• Write guidance on how someone should target both .NET Core 3.1 (x64) and .NET 6 (Arm64) on the same machine. Say they are working on two different apps, day in and day out. How do they make that efficient and delightful? This might inspire/require us to make more product changes.