Remove net472 containers

[YuliiaKovalova]

Summary

Remove the net472 target from the Containers SDK (Microsoft.NET.Build.Containers), keeping only the .NET Core ($(SdkTargetFramework)) target.

The net472 build existed to support Visual Studio's Full-Framework MSBuild (MSBuildRuntimeType == Full). Now that VS uses .NET Runtime with HostObject support for container operations, the net472 target and all this infrastructure is no longer needed.

Fixes

dotnet/msbuild#11333

[YuliiaKovalova]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[Copilot]

Pull request overview

This PR removes the net472 target and associated packaging/test/layout infrastructure from the Containers SDK (Microsoft.NET.Build.Containers), aligning with the move away from Full Framework MSBuild for VS container operations.

Changes:

• Drop multi-targeting ($(SdkTargetFramework);net472) for Microsoft.NET.Build.Containers and related integration tests, removing net472-only source/test shims.
• Remove net472 task publishing/packaging outputs (layout + nupkg content) and update package content expectations accordingly.
• Update the shipped .props to always point at the .NET (net10.0) task implementation.

Reviewed changes

Copilot reviewed 15 out of 15 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
test/UnitTests.proj	Stops including Containers integration tests in the TestFullMSBuild/net472 run.
test/Microsoft.NET.Build.Containers.IntegrationTests/PackageTests.cs	Updates dependency and nupkg content assertions to remove tasks/net472 expectations.
test/Microsoft.NET.Build.Containers.IntegrationTests/Microsoft.NET.Build.Containers.IntegrationTests.csproj	Removes net472 target and related conditional compilation setup.
test/Microsoft.NET.Build.Containers.IntegrationTests/FullFramework/CreateNewImageToolTaskTests.cs	Deletes Full Framework–specific tests for the removed ToolTask-based implementation.
src/Layout/redist/targets/GenerateLayout.targets	Removes publishing of net472 task assets into the redist layout.
src/Layout/redist/targets/Crossgen.targets	Updates comment to reflect removal of net472 components.
src/Containers/packaging/package.csproj	Removes net472 packaging path and dependency harvesting for net472 tasks.
src/Containers/packaging/build/Microsoft.NET.Build.Containers.props	Removes MSBuild runtime-based TFM selection; uses only net10.0 tasks and updates UsingTask declarations.
src/Containers/Microsoft.NET.Build.Containers/net472Definitions.cs	Deletes net472-only polyfills (IsExternalInit, NotNullWhenAttribute).
src/Containers/Microsoft.NET.Build.Containers/Tasks/CreateNewImageToolTask.cs	Deletes the net472 ToolTask-based shim implementation.
src/Containers/Microsoft.NET.Build.Containers/Tasks/ComputeDotnetBaseImageAndTag.cs	Removes now-unused NETFRAMEWORK-only using directives.
src/Containers/Microsoft.NET.Build.Containers/PublicAPI/net472/PublicAPI.Unshipped.txt	Removes net472 public API baseline.
src/Containers/Microsoft.NET.Build.Containers/PublicAPI/net472/PublicAPI.Shipped.txt	Removes net472 public API baseline header.
src/Containers/Microsoft.NET.Build.Containers/Microsoft.NET.Build.Containers.csproj	Removes net472 TFM and all net472-specific compile/package reference conditionals.
src/Containers/Microsoft.NET.Build.Containers/ContainerHelpers.cs	Removes NETFRAMEWORK/NET conditional usings now that net472 is gone.

[baronfel]

This looks correct, however anyone still using the Microsoft.Net.Build.Containers NuGet package and using an older version of VS will be broken if they upgrade. We need to stop publishing the package now that it's baked into the SDK too.

[YuliiaKovalova]

This looks correct, however anyone still using the Microsoft.Net.Build.Containers NuGet package and using an older version of VS will be broken if they upgrade. We need to stop publishing the package now that it's baked into the SDK too.

@marcpopMSFT & @mmitche could you please check this comment? Do you have any concerns regarding removing this package from publishing?

[mmitche]

This looks correct, however anyone still using the Microsoft.Net.Build.Containers NuGet package and using an older version of VS will be broken if they upgrade. We need to stop publishing the package now that it's baked into the SDK too.

@marcpopMSFT & @mmitche could you please check this comment? Do you have any concerns regarding removing this package from publishing?

Only concern is that it shows up as a package ref somewhere we don't expect, but we should find that in testing. Mark the package as non-shipping and I think that should about do it.