[SimaTian]

Fixes dotnet/msbuild#13774

Migrates \GenerateDepsFile\ to support \IMultiThreadableTask.

Changes

• Adds [MSBuildMultiThreadableTask]\ attribute and implements \IMultiThreadableTask.
• Absolutizes \ProjectPath\ and \DepsFilePath\ in \ExecuteCore; scopes \AssetsFilePath\ / \RuntimeGraphPath\ absolutization inside \WriteDepsFile\ (point-of-use).
• \DepsFilePath\ is backed by \AbsolutePath\ throughout: \File.Create\ uses .Value; \FilesWritten\ output uses .OriginalValue\ to preserve user-supplied relativity.
• Adds 6 behavioral tests: output-relativity preservation, ProjectPath absolutization, decoy-CWD resolution, cross-thread env-var isolation, multi-process parity, concurrent execution.

Addresses AR-May findings from #52936

• ✅ ProjectPath absolutized at task level before passing to \DependencyContextBuilder.
• ✅ Absolutization moved into \WriteDepsFile\ helper (point-of-use).
• ✅ \FilesWritten\ uses \AbsolutePath.OriginalValue\ (output fidelity).

Supersedes

Part of the split of stuck merge-group PR #52936. This is the 2-of-5 split for \GenerateDepsFile.

[Copilot]

Pull request overview

Migrates GenerateDepsFile to support MSBuild multithreaded execution by implementing IMultiThreadableTask, using TaskEnvironment for path resolution, and adding unit tests intended to validate correctness under concurrent execution / non-default working directories.

Changes:

• Add [MSBuildMultiThreadableTask] and implement IMultiThreadableTask on GenerateDepsFile, including TaskEnvironment handling.
• Absolutize ProjectPath/DepsFilePath before writing and move AssetsFilePath/RuntimeGraphPath absolutization to point-of-use.
• Add a new multithreading-focused unit test suite for GenerateDepsFile.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 4 comments.

File	Description
src/Tasks/Microsoft.NET.Build.Tasks/GenerateDepsFile.cs	Adds IMultiThreadableTask support and adjusts path handling for multithread-safe execution and output fidelity.
src/Tasks/Microsoft.NET.Build.Tasks.UnitTests/GivenAGenerateDepsFileMultiThreading.cs	Adds behavioral/concurrency tests for GenerateDepsFile in multithreaded / CWD-sensitive scenarios.

[AlesProkop]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 2 pipeline(s).

[jankratochvilcz]

Few minor changes, but no significant issues that I see ✨

[jankratochvilcz]

Looks good, no more concerns from me!

[OvesN]

Please recheck the flow of all paths that we receive as inputs. They can touch forbidden APIs. Mb there is more than I commented. Can analyzer help here?

[AlesProkop]

Summary

Eliminate analyzer-flagged unsafe-API calls on the GenerateDepsFile → WriteDepsFile graph; route all path/env access through TaskEnvironment.

• FrameworkReferenceResolver — dropped parameterless ctor; GenerateDepsFile now passes TaskEnvironment.GetEnvironmentVariable.
• GenerateDepsFile — File.Create(depsFilePath) uses the AbsolutePath overload; AssetsFilePath / RuntimeGraphPath go through string.IsNullOrEmpty(...) ? null : TaskEnvironment.GetAbsolutePath(...) to preserve prior null/empty semantics; both DependencyContextBuilder ctors get TaskEnvironment.GetAbsolutePath injected.
• DependencyContextBuilder — new _getAbsolutePath field + GetAbsolutePath helper; CreateRuntimeFile now takes AbsolutePath fullPath; GetRuntimeLibrary and GetRuntimePackLibraries wrap raw Path strings through GetAbsolutePath before File.Exists / CreateRuntimeFile.
• DependencyContextBuilder.GetProjectInfo — keeps Path.GetFullPath(Path.Combine(...)) for the _referenceProjectInfos lookup key (canonical MSBuildSourceProjectFile); AbsolutePath would preserve .. and miss the lookup. Pure string key, no file I/O, so MSBuildTask0003 doesn't apply.
• FileUtilities — added AbsolutePath overloads for GetFileVersion / TryGetAssemblyVersion, plus GetAssemblyVersion(AbsolutePath) in FileUtilities.MetadataReader.cs. Legacy string overloads retained for unmigrated callers (ResolvePackageFileConflicts, GenerateRegFreeComManifest); their MSBuildTask0005 transitive hits are out of scope.