Multi-arch container publishing conflicts with the --output option in dotnet publish

[baronfel]

Describe the bug

Invoking a multi-arch container publish of a project while also overriding the PublishDir results in the per-RID inner builds all having the same PublishDir. This results in race conditions during the build, and if there are any native, RID-specific assets in the build can result in mixing assets for different platforms.

To Reproduce

Using .NET SDK 9.0.102 or .NET SDK 8.0.405 or later,

• dotnet new webapi
• Add <RuntimeIdentifiers>linux-x64;linux-arm64</RuntimeIdentifiers>
• run dotnet publish -t:PublishContainer --output <some directory>
• watch the MSB3026 warnings fly:

>dotnet publish -t:PublishContainer -v d -bl -o bugsville
Restore complete (0.5s)
    Determining projects to restore...
    Restored E:\Code\Scratch\multi-arch-build-bug\multi-arch-build-bug.csproj (in 217 ms).
C:\Program Files\dotnet\sdk\9.0.102\Sdks\Microsoft.NET.Sdk\targets\Microsoft.NET.Publish.targets(355,5): warning MSB3026: Could not copy "E:\Code\Scratch\multi-arch-build-bug\bugsville\bugsville\multi-arch-build-bug.runtimeconfig.json" to "E:\Code\Scratch\multi-arch-build-bug\bugsville\bugsville\bugsville\multi-arch-build-bug.runtimeconfig.json". Beginning retry 1 in 1000ms. The process cannot access the file 'E:\Code\Scratch\multi-arch-build-bug\bugsville\bugsville\bugsville\multi-arch-build-bug.runtimeconfig.json' because it is being used by another process.
C:\Program Files\dotnet\sdk\9.0.102\Sdks\Microsoft.NET.Sdk\targets\Microsoft.NET.Publish.targets(355,5): warning MSB3026: Could not copy "E:\Code\Scratch\multi-arch-build-bug\bugsville\bugsville\multi-arch-build-bug.runtimeconfig.json" to "E:\Code\Scratch\multi-arch-build-bug\bugsville\bugsville\bugsville\multi-arch-build-bug.runtimeconfig.json". Beginning retry 1 in 1000ms. The process cannot access the file 'E:\Code\Scratch\multi-arch-build-bug\bugsville\bugsville\multi-arch-build-bug.runtimeconfig.json' because it is being used by another process.
  multi-arch-build-bug succeeded (3.5s) → bugsville\
    Building image 'multi-arch-build-bug' with tags 'latest-linux-x64' on top of base image 'mcr.microsoft.com/dotnet/aspnet:9.0'.
    Pushed image 'multi-arch-build-bug:latest-linux-x64' to local registry via 'docker'.
  multi-arch-build-bug succeeded with 1 warning(s) (5.4s) → bugsville\
    C:\Program Files\dotnet\sdk\9.0.102\Sdks\Microsoft.NET.Sdk\targets\Microsoft.NET.Publish.targets(355,5): warning MSB3026: Could not copy "E:\Code\Scratch\multi-arch-build-bug\bugsville\bugsville\multi-arch-build-bug.runtimeconfig.json" to "E:\Code\Scratch\multi-arch-build-bug\bugsville\bugsville\bugsville\multi-arch-build-bug.runtimeconfig.json". Beginning retry 1 in 1000ms. The process cannot access the file 'E:\Code\Scratch\multi-arch-build-bug\bugsville\bugsville\multi-arch-build-bug.runtimeconfig.json' because it is being used by another process.
    Building image 'multi-arch-build-bug' with tags 'latest-linux-arm64' on top of base image 'mcr.microsoft.com/dotnet/aspnet:9.0'.
    Pushed image 'multi-arch-build-bug:latest-linux-arm64' to local registry via 'docker'.
  multi-arch-build-bug succeeded with 1 warning(s) (4.2s) → bugsville\
    C:\Program Files\dotnet\sdk\9.0.102\Sdks\Microsoft.NET.Sdk\targets\Microsoft.NET.Publish.targets(355,5): warning MSB3026: Could not copy "E:\Code\Scratch\multi-arch-build-bug\bugsville\bugsville\multi-arch-build-bug.runtimeconfig.json" to "E:\Code\Scratch\multi-arch-build-bug\bugsville\bugsville\bugsville\multi-arch-build-bug.runtimeconfig.json". Beginning retry 1 in 1000ms. The process cannot access the file 'E:\Code\Scratch\multi-arch-build-bug\bugsville\bugsville\bugsville\multi-arch-build-bug.runtimeconfig.json' because it is being used by another process.

Build succeeded with 2 warning(s) in 11.0s

Details

What's happening here is that the --output CLI arg is passing the PublishDir global property with a value of bugsville to MSBuild. This is used for the 'outer' publish successfully, but because a multi-arch container publish is triggered, we do two RID-specific inner publishes in parallel. These are done with the same values of PublishDir, which causes the conflicts.

Potential solutions

• provide a knob to stop the parallel inner builds
• use AdditionalProperties on the inner builds to set a new value of PublishDir
• have --output mean a different property for a multi-RID build and define what PublishDir should be in terms of that property
• I'm sure there are other options
• Set RemoveProperties on the MSBuild Task invocations for the inner builds

Commentary

This is coming up because, unlike for multi-TFM builds, we're not blocking publishing for multiple RIDs. The Publish target for multi-targeted builds even says:

Currently it is unsupported to publish for multiple target frameworks
   because users can specify the $(PublishDir), and publish would put
   multiple published applications in a single directory.

Yet here we are.