dotnet · danroth27 · May 28, 2026
@@ -0,0 +1,78 @@
+# MSBuild in .NET 11 Preview 5 - Release Notes
+
+.NET 11 Preview 5 includes new MSBuild features & enhancements:
+
+- [Multithreaded builds can be enabled from the environment](#multithreaded-builds-can-be-enabled-from-the-environment)
+- [MSBuild evaluation and item filtering are faster](#msbuild-evaluation-and-item-filtering-are-faster)
+- [Binary log replay handles older logs](#binary-log-replay-handles-older-logs)
+- [MSBuild runs on Haiku](#msbuild-runs-on-haiku)
+
+These features continue the .NET 11 work on [Multithreaded execution](https://github.com/dotnet/msbuild/blob/main/documentation/specs/multithreading/multithreaded-msbuild.md), logging, and evaluation performance.
+
+## Multithreaded builds can be enabled from the environment
+
+MSBuild now supports `MSBUILDFORCEMULTITHREADED=1`, an environment-variable equivalent of the `-multiThreaded` / `-mt` command-line switch ([dotnet/msbuild #13662](https://github.com/dotnet/msbuild/pull/13662)). This helps CI systems, IDEs, and wrapper scripts opt in to multithreaded builds when they cannot easily add a command-line switch.
+
+```shell
+set MSBUILDFORCEMULTITHREADED=1
+dotnet build MySolution.sln
+```
+
+Preview 5 also moves more in-box tasks onto the multithreaded execution model. These tasks now use the task environment for project-relative paths instead of relying on process-wide current-directory state:
+
+- `AssignProjectConfiguration` ([dotnet/msbuild #13615](https://github.com/dotnet/msbuild/pull/13615))
+- `GetAssemblyIdentity` ([dotnet/msbuild #13588](https://github.com/dotnet/msbuild/pull/13588))
+- `GetInstalledSDKLocations` ([dotnet/msbuild #13564](https://github.com/dotnet/msbuild/pull/13564))
+- Manifest tasks, including `GenerateApplicationManifest`, `GenerateDeploymentManifest`, `ResolveManifestFiles`, `AddToWin32Manifest`, `UpdateManifest`, and `CreateManifestResourceName` ([dotnet/msbuild #13177](https://github.com/dotnet/msbuild/pull/13177))
+- `ResolveAssemblyReference` ([dotnet/msbuild #13319](https://github.com/dotnet/msbuild/pull/13319))
+
+## MSBuild evaluation and item filtering are faster
+
+MSBuild's escaping helpers now allocate less and run faster in evaluation-heavy workloads ([dotnet/msbuild #13426](https://github.com/dotnet/msbuild/pull/13426)). `EscapingUtilities.Escape` and `EscapingUtilities.UnescapeAll` are used throughout property and item evaluation. In the PR benchmarks on .NET 10.0, `Escape_NoSpecialChars` improved from `17.96 ns` to `5.37 ns`, `Escape_FewSpecialChars` improved from `191.8 ns` to `84.9 ns`, and `UnescapeAll_InvalidEscapeSequences` dropped its allocation from `48 B` to `0 B`.
+
+Item filtering also returns to linear behavior for large item sets with many batched removes ([dotnet/msbuild #13688](https://github.com/dotnet/msbuild/pull/13688)). This fixes a regression seen in QtMsBuild C++ projects where builds with tens of thousands of items could spend hours in `Lookup.GetItems`. The result construction path is back to `O(N + A + M)` instead of `O((N + A) x M)` for the affected pattern.
+
+## Binary log replay handles older logs
+
+Command-line binary log replay now replays older MSBuild logs instead of rejecting them completely when the log version is lower than the current tool version ([dotnet/msbuild #13608](https://github.com/dotnet/msbuild/pull/13608)). MSBuild skips entries it cannot understand and prints the version warning after replay, so older `.binlog` files still provide the events that are compatible with the current replay engine.
+
+```shell
+dotnet msbuild -bl:build.binlog MyProject.csproj
+dotnet msbuild build.binlog
+```
+
+## MSBuild runs on Haiku
+
+MSBuild now recognizes Haiku as a Unix-like operating system ([dotnet/msbuild #13607](https://github.com/dotnet/msbuild/pull/13607)). This lets MSBuild choose the same shared Unix paths as Linux and macOS, such as invoking `.sh` scripts instead of `.cmd` scripts when it runs on Haiku.
+
+Thank you [@trungnt2910](https://github.com/trungnt2910) for this contribution!
+
+<!-- Filtered features (significant engineering work, but too niche for release notes):
+  - Terminal Logger task input logging: fixed a major performance trap but fits better as a bug fix because it restores expected logger overhead instead of adding a new user workflow.
+  - SkipNonexistentTargets through metaprojects: important correctness fix for specialized project-reference dispatch, but not broad enough for a feature section.
+  - RestoreTask transient TaskHost routing: important server and multithreaded-mode reliability fix, but it is an implementation detail of task isolation.
+  - UsingTask Runtime="NET" default architecture: prevents x86 .NET Framework hosts from looking for an unshipped x86 .NET task host, but it is a narrow compatibility fix.
+  - Haiku support: included despite narrow platform scope because it is a clear platform enablement change and a community contribution.
+-->
+
+## Bug fixes
+
+- **Build engine**
+  - `BuildManager.ShutdownAllNodes()` now finds AppHost-launched worker nodes, so `dotnet build-server shutdown` can clean up `MSBuild.exe` nodes started by a `dotnet`-hosted build ([dotnet/msbuild #13511](https://github.com/dotnet/msbuild/pull/13511)).
+  - MSBuild no longer uses WMI to scan command lines while identifying worker processes on Windows, removing latency on machines with many `dotnet` processes ([dotnet/msbuild #13610](https://github.com/dotnet/msbuild/pull/13610)).
+- **Logging**
+  - Terminal Logger no longer opts in to task input logging that it does not consume, avoiding serialization of large task parameter payloads on every task invocation ([dotnet/msbuild #13686](https://github.com/dotnet/msbuild/pull/13686)).
+  - MSBuild prints the existing auto-response-file warning before `MSB1008` when switches from `MSBuild.rsp` or `Directory.Build.rsp` cause multiple projects to be specified ([dotnet/msbuild #13675](https://github.com/dotnet/msbuild/pull/13675)).
+- **Project references**
+  - `SkipNonexistentTargets="true"` now propagates through generated metaprojects, so project-reference builds do not fail with `MSB4057` when the underlying project lacks the optional target ([dotnet/msbuild #13650](https://github.com/dotnet/msbuild/pull/13650)).
+- **Tasks**
+  - `WriteLinesToFile` transactional overwrites now handle parallel writers that create the destination between the replace check and move operation ([dotnet/msbuild #13477](https://github.com/dotnet/msbuild/pull/13477)).
+  - The `Copy` task now retries `ERROR_ACCESS_DENIED` on non-Windows instead of treating it as a Windows-style read-only-file failure ([dotnet/msbuild #13479](https://github.com/dotnet/msbuild/pull/13479)).
+  - `UsingTask Runtime="NET"` without an explicit `Architecture` now defaults to the OS architecture, matching the `dotnet` host MSBuild launches for .NET task hosts ([dotnet/msbuild #13741](https://github.com/dotnet/msbuild/pull/13741)).
+  - `RestoreTask` now runs in a transient TaskHost when MSBuild server or multithreaded mode would otherwise let NuGet static state leak across invocations ([dotnet/msbuild #13660](https://github.com/dotnet/msbuild/pull/13660)).
+
+## Community contributors
+
+Thank you contributors! ❤️
+
+- [@trungnt2910](https://github.com/dotnet/msbuild/pulls?q=is%3Apr+is%3Amerged+author%3Atrungnt2910)