[SimaTian]

Fixed dotnet/msbuild#13777

Migrate ResolvePackageFileConflicts to IMultiThreadableTask

Migrates ResolvePackageFileConflicts (MSBuild task in Microsoft.NET.Build.Tasks) to support concurrent multi-threaded execution by implementing IMultiThreadableTask with a TaskEnvironment property.

Why

From OrchardCore build profiling (see gist):

Metric	Value
Invocations	193
Cold-build time	1,188 ms
Incremental-build time	713 ms (60% of cold — biggest incremental tax of any NET.Sdk task)
Log messages	5,836 (never reduced on incremental)

This migration does not address the incremental-build regression or log-volume issue directly but enables the task to run safely under the upcoming multi-threaded MSBuild execution model.

What changed

• Task now carries [MSBuildMultiThreadableTask] and implements IMultiThreadableTask with a TaskEnvironment property.
• All Path.GetFullPath / File.* / Directory.* / env-var callsites in ResolvePackageFileConflicts.cs and its helpers (including the shared ConflictResolution/ path) routed through TaskEnvironment so they resolve against the task's project directory rather than process CWD.
• Output properties preserve relativity via AbsolutePath.OriginalValue — no user-observable change in task outputs.

Tests

• New GivenAResolvePackageFileConflictsMultiThreading.cs behavioural tests: decoy-CWD path resolution, multi-process vs multi-threaded parity, output relativity, concurrent execution with xUnit [Collection("CwdSensitive")] for safety.
• Existing tests unchanged & passing.

Review status

Internally reviewed via 3-round playbook (merge-group-review → expert-review-msbuild-migration → opus-4.7 adversarial). All rounds PASS.

Depends on polyfills infrastructure (already in main via #52909).

[Copilot]

Pull request overview

This PR migrates ResolvePackageFileConflicts (a shared conflict-resolution MSBuild task) to participate in MSBuild’s upcoming multi-threaded execution model by implementing IMultiThreadableTask and routing relative path resolution through TaskEnvironment (project-directory rooted), with accompanying behavioral tests to validate CWD-independence and concurrency behavior.

Changes:

• Mark ResolvePackageFileConflicts as multi-threadable and add a TaskEnvironment property used to resolve relative inputs against the project directory.
• Plumb a path-resolver into ConflictItem so file existence/version reads operate on resolved (project-rooted) absolute paths.
• Add new unit tests validating project-dir-based path resolution, parity across differing CWDs, output relativity, and concurrent execution behavior.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
src/Tasks/Microsoft.NET.Build.Tasks.UnitTests/GivenAResolvePackageFileConflictsMultiThreading.cs	Adds behavioral tests for CWD independence, output relativity, and concurrent execution.
src/Tasks/Common/ConflictResolution/ResolvePackageFileConflicts.cs	Implements IMultiThreadableTask, introduces TaskEnvironment, and uses it to resolve relative paths for manifests/TFDs and conflict items.
src/Tasks/Common/ConflictResolution/ConflictItem.cs	Adds optional path resolver and uses it for file I/O (exists and version reads).

[jankratochvilcz]

Looks good! Left a couple of minor comments :-)

[jankratochvilcz]

Left one bit, please check it out :-)

[jankratochvilcz]

Looks good, thank you!

[AR-May]

Have not yet finished with reviewing this PR. Publishing intermediate comments.

[AR-May]

Overall looks good! My only unresolved question concerns the behavioral change in #53943 (comment)

[jankratochvilcz]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s), but failed to run 1 pipeline(s).

[jankratochvilcz]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s), but failed to run 1 pipeline(s).

[jankratochvilcz]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s), but failed to run 1 pipeline(s).