[JanProvaznik]

Fixes #12099

Context

The MSBuild server public surface lived in Microsoft.Build.Experimental. If the server is to become a supported, on-by-default feature, these types should not be in the Experimental namespace. This moves them to a new dedicated Microsoft.Build.Server namespace.

This mirrors the ProjectCache promotion (#12051), but as a clean break (no obsolete shim types) because — unlike ProjectCache, which had external plugin assemblies compiled against the old namespace — research found no external consumers of the server types:

• dotnet/sdk: 0 references
• dotnet/roslyn: 0 references
• org:dotnet code search: only dotnet/msbuild, the dotnet/dotnet VMR mirror, msbuild-api-docs, and source-build reference packages
• VS (DevDiv/VS): no code consumers — only an ApiCompat backward-compatibility baseline lists these types
• Within MSBuild: only internal consumers + unit tests

Changes

Moved to Microsoft.Build.Server:

• MSBuildClient
• MSBuildClientExitResult
• MSBuildClientExitType
• OutOfProcServerNode (incl. nested public delegate BuildCallback)

Updated internal consumers and tests:

• BuildManager.cs, NodeProviderOutOfProcBase.cs (doc cref), MSBuildClientApp.cs, XMake.cs
• MSBuildClient_Tests.cs, RedirectConsoleWriter_Tests.cs, MSBuildServer_Tests.cs

Compatibility:

• src/Build/CompatibilitySuppressions.xml: added 16 CP0001 suppressions (4 removed types × {lib,ref} × {net472,net11.0}), auto-generated via ApiCompatGenerateSuppressionFile, with a comment noting they can be removed once the package-validation baseline advances past this change. Package validation reported only type-level CP0001 (no CP0002), confirming no other public API references these types in its signature.

Docs:

• documentation/MSBuild-Server.md: noted that the public server entry points now live under Microsoft.Build.Server.

Breaking change

This is an intentional binary-breaking change to a previously Experimental surface (a namespace rename within the same assembly cannot be type-forwarded). It should be noted in release/breaking-change notes. api-docs and source-build reference packages regenerate automatically from the shipped assembly.

VS insertion coordination

The VS ApiCompat backward-compatibility test (microsoft.build-suppressions.xml) treats the shipped public surface as a contract and will flag the removed Microsoft.Build.Experimental.* server types. A matching VS-side suppressions update is required on insertion, mirroring how #12051 was coordinated.

Testing

• Full build.cmd: 0 warnings, 0 errors
• Package validation passes against baseline 18.10.0-1.26378.2 (regenerated for net11.0 after main moved off net10.0)
• Targeted tests pass on net472 + net11.0: MSBuildClient unreachable-server fallback, RedirectConsoleWriter, and end-to-end CanShutdownServerProcess (real server start + shutdown via both BuildManager and MSBuildClient)

Out of scope (separate work)

• Enabling the server by default (would need a Change Wave)
• The Microsoft.Build.Experimental.FileAccess / BuildCheck / ProjectCache sub-namespaces

Co-authored-by: Copilot 223556219+Copilot@users.noreply.github.com

[JanProvaznik]

The restore task requiring the taskhost workaround is ship blocking... It regresses performance.
I'll keep this as draft for now, but I think breaking change of changing is ok given clear indication this is experimental and no known users

[Copilot]

Pull request overview

Promotes the MSBuild server public surface area out of Microsoft.Build.Experimental into a supported Microsoft.Build.Server namespace, and updates CLI, engine, tests, and docs accordingly.

Changes:

• Moved server-related public types (MSBuildClient, MSBuildClientExitResult, MSBuildClientExitType, OutOfProcServerNode) to Microsoft.Build.Server.
• Updated internal call sites and unit tests to reference the new namespace.
• Updated package-validation suppressions and documentation for the namespace move.

Reviewed changes

Copilot reviewed 13 out of 13 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/MSBuild/XMake.cs	Switched CLI usage/imports to Microsoft.Build.Server.
src/MSBuild/MSBuildClientApp.cs	Updated client app imports to Microsoft.Build.Server.
src/MSBuild.UnitTests/MSBuildServer_Tests.cs	Updated test imports to Microsoft.Build.Server.
src/Build/CompatibilitySuppressions.xml	Added CP0001 suppressions for removed Microsoft.Build.Experimental.* server types (note: see review comment about missing net10 suppressions).
src/Build/BackEnd/Node/OutOfProcServerNode.cs	Moved OutOfProcServerNode into Microsoft.Build.Server.
src/Build/BackEnd/Components/Communications/NodeProviderOutOfProcBase.cs	Updated XML doc cref to the new namespace.
src/Build/BackEnd/Client/MSBuildClientExitType.cs	Moved enum into Microsoft.Build.Server and improved doc comment.
src/Build/BackEnd/Client/MSBuildClientExitResult.cs	Moved type into Microsoft.Build.Server and updated summary text.
src/Build/BackEnd/Client/MSBuildClient.cs	Moved MSBuildClient into Microsoft.Build.Server.
src/Build/BackEnd/BuildManager/BuildManager.cs	Updated shutdown call to Microsoft.Build.Server.MSBuildClient.
src/Build.UnitTests/BackEnd/RedirectConsoleWriter_Tests.cs	Updated test imports to Microsoft.Build.Server.
src/Build.UnitTests/BackEnd/MSBuildClient_Tests.cs	Updated test imports to Microsoft.Build.Server.
documentation/MSBuild-Server.md	Documented the new public namespace for server entry points.

Comments suppressed due to low confidence (1)

src/Build/CompatibilitySuppressions.xml:66

• Compatibility suppressions were added only for the net472 lib/ref assets. If package validation compares the net10.0 assets against the baseline as well, the removed Microsoft.Build.Experimental.* server types will still trigger CP0001 for lib/net10.0 and ref/net10.0. The PR description also mentions 16 suppressions (including net10.0), but the file currently contains only 8.

  </Suppression>
  <Suppression>
    <DiagnosticId>PKV006</DiagnosticId>
    <Target>net10.0</Target>
  </Suppression>

[rainersigwald]

This mirrors the ProjectCache promotion (#12051), but as a clean break (no obsolete shim types) because — unlike ProjectCache, which had external plugin assemblies compiled against the old namespace — research found no external consumers of the server types:

This suggests to me that maybe we shouldn't make it public at all? Rename the namespace but keep it internal?

[JanProvaznik]

This suggests to me that maybe we shouldn't make it public at all? Rename the namespace but keep it internal?

@rainersigwald that'd require Microsoft.Build.csproj InternalsVisibleTo MSBuild.csproj, which I don't have enough context about, but I thought it's intentionally not done so that API consumers can achieve all engine functionality without the cli itself.

[rainersigwald]

Ah, that's a good blocking function. We should update the comments to indicate that we don't expect third-party use of these APIs though--they basically only work to wrap the CLI so invoke the CLI instead.

[JanProvaznik]

Done in 9a850b7.

All four types (plus the nested OutOfProcServerNode.BuildCallback delegate) are now marked [EditorBrowsable(EditorBrowsableState.Never)] so they don't surface in IntelliSense, and each carries a <remarks> block:

This type is public only so that the MSBuild command-line application can host the MSBuild server; third-party use is not expected or supported. It exists to wrap the MSBuild CLI and offers nothing beyond it, so invoke the CLI instead.

Also noted the same in documentation/MSBuild-Server.md. Verified the attribute survives into the shipped reference assemblies for both ref/net472 and ref/net11.0.