plumbing taskenvironment through execution

[JanProvaznik]

rework of #12608 after merging #12651
fixes #11829, #11830 #12850 #12802

Context

Changes Made

1. refactor communicationutilities to support the taskenvironmentdrivers
2. propagate taskenvironment throughout execution
3. enlightening intrinsic tasks

Testing

simple sample projects using the intrinsictasks build

Notes

"normal tasks" will be enlightened in subsequent PRs
included the intrinsic tasks in this PR so it's integration testable

[Copilot]

Pull request overview

This PR implements support for the TaskEnvironment infrastructure to enable thread-safe task execution in MSBuild's multithreaded execution model. The changes plumb TaskEnvironment through the entire execution pipeline, from build request creation through task execution, with appropriate change wave gating (Wave18_3) to ensure backward compatibility.

Key Changes

• TaskEnvironment Integration: Added TaskEnvironment property to MSBuild and CallTarget tasks (both intrinsic and external versions), implementing IMultiThreadableTask interface
• Change Wave Protection: All changes are properly gated behind ChangeWaves.Wave18_3 to maintain backward compatibility
• Test Infrastructure: New helper class (TaskEnvironmentHelper) and comprehensive integration tests (MSBuildMultithreaded_Tests) to validate environment isolation in both multi-threaded and multi-process modes

Reviewed changes

Copilot reviewed 36 out of 36 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
src/UnitTests.Shared/TaskEnvironmentHelper.cs	New helper class for creating TaskEnvironment instances in tests
src/Tasks/MSBuild.cs	Added IMultiThreadableTask support and TaskEnvironment property to external MSBuild task
src/Tasks/CallTarget.cs	Added IMultiThreadableTask support and TaskEnvironment property to external CallTarget task
src/Tasks.UnitTests/MSBuild_Tests.cs	Updated all test instances to use CreateMSBuildTask helper with proper TaskEnvironment initialization
src/Shared/UnitTests/CommunicationUtilities_Tests.cs	Updated to use IReadOnlyDictionary for environment variables
src/Shared/CommunicationsUtilities.cs	Added CLR2COMPATIBILITY handling for SetEnvironment with IReadOnlyDictionary parameter
src/MSBuild/OutOfProcTaskHostNode.cs	Updated environment variable handling to support IReadOnlyDictionary
src/MSBuild.UnitTests/MSBuildMultithreaded_Tests.cs	New integration test class with EnvironmentIsolationTestTask for validating TaskEnvironment behavior
src/Framework/TaskEnvironment.cs	Updated SetEnvironment to use IReadOnlyDictionary parameter
src/Framework/ITaskEnvironmentDriver.cs	Updated SetEnvironment interface to use IReadOnlyDictionary parameter
src/Framework/ChangeWaves.cs	Added Wave18_3 for gating new TaskEnvironment features
src/Build/Instance/TaskFactories/TaskHostTask.cs	Added TaskEnvironment support with change wave gating for environment restoration
src/Build/Instance/TaskFactories/AssemblyTaskFactory.cs	Updated CreateTaskInstance to accept and pass TaskEnvironment parameter
src/Build/BackEnd/TaskExecutionHost/TaskExecutionHost.cs	Added TaskEnvironment property and logic to set it on IMultiThreadableTask instances
src/Build/BackEnd/TaskExecutionHost/MultiThreadedTaskEnvironmentDriver.cs	Updated SetEnvironment to use IReadOnlyDictionary
src/Build/BackEnd/TaskExecutionHost/MultiProcessTaskEnvironmentDriver.cs	Updated SetEnvironment and changed to use NativeMethodsShared.SetCurrentDirectory
src/Build/BackEnd/Shared/IBuildResults.cs	Changed SavedEnvironmentVariables from FrozenDictionary to IReadOnlyDictionary
src/Build/BackEnd/Shared/BuildResult.cs	Updated serialization logic to handle IReadOnlyDictionary for environment variables
src/Build/BackEnd/Shared/BuildRequestConfiguration.cs	Changed SavedEnvironmentVariables from FrozenDictionary to IReadOnlyDictionary
src/Build/BackEnd/Components/RequestBuilder/TaskBuilder.cs	Added SetTaskEnvironment method and change wave gated logic to set project directory via TaskEnvironment
src/Build/BackEnd/Components/RequestBuilder/TargetBuilder.cs	Added change wave gated logic to set/clear TaskEnvironment on task builder
src/Build/BackEnd/Components/RequestBuilder/RequestBuilder.cs	Renamed SetProjectCurrentDirectory to SetProjectDirectory, added change wave gating for TaskEnvironment operations
src/Build/BackEnd/Components/RequestBuilder/IntrinsicTasks/MSBuild.cs	Added IMultiThreadableTask support, TaskEnvironment property, and using TaskEnvironment.GetAbsolutePath for path resolution
src/Build/BackEnd/Components/RequestBuilder/IntrinsicTasks/CallTarget.cs	Added IMultiThreadableTask support and TaskEnvironment property to intrinsic CallTarget
src/Build/BackEnd/Components/RequestBuilder/ITaskBuilder.cs	Added SetTaskEnvironment method to interface
src/Build/BackEnd/Components/BuildRequestEngine/BuildRequestEntry.cs	Added TaskEnvironment parameter to constructor and property
src/Build/BackEnd/Components/BuildRequestEngine/BuildRequestEngine.cs	Added logic to create appropriate TaskEnvironment based on MultiThreaded build parameter
src/Build/BackEnd/BuildManager/BuildParameters.cs	Changed MultiThreaded property to use backing field for proper serialization
src/Build.UnitTests/BackEnd/*	Updated all test files to provide TaskEnvironment when creating BuildRequestEntry instances

Comments suppressed due to low confidence (1)

src/Build/BackEnd/Components/RequestBuilder/RequestBuilder.cs:1497

• This foreach loop implicitly filters its target sequence - consider filtering the sequence explicitly using '.Where(...)'.

            foreach (KeyValuePair<string, string> entry in savedEnvironment)
            {
                // If the environment doesn't have the variable set, or if its value differs from what we have saved, set it
                // to the saved value.  Doing the comparison before setting is faster than unconditionally setting it using
                // the API.
                if (!currentEnvironment.TryGetValue(entry.Key, out string value) || !String.Equals(entry.Value, value, StringComparison.Ordinal))
                {
                    Environment.SetEnvironmentVariable(entry.Key, entry.Value);
                }
            }

---

You can also share your feedback on Copilot code review for a chance to win a $100 gift card. Take the survey.

[JanProvaznik]

https://devdiv.visualstudio.com/DevDiv/_git/VS/pullrequest/691867 insertion validation ETA tomorrow

[JanProvaznik]

flagging why I think changewave is not necessary, the taskenv for multiprocess is a pretty clean wrap