Fix System.IO.File/Directory property functions with relative paths in -mt mode

[JanProvaznik]

Summary

Property functions like False and False resolved relative paths against Environment.CurrentDirectory (process-global), which produces wrong results in -mt mode where multiple projects build concurrently on different threads sharing the same process.

This change resolves relative path arguments against FileUtilities.CurrentThreadWorkingDirectory (the thread-local working directory set by the multithreaded task environment driver), matching the existing behavior of Path.GetFullPath which was already intercepted in WellKnownFunctions.

Changes

src/Shared/FileUtilities.cs

• Add MakeFullPathFromThreadWorkingDirectory(string path) helper that resolves relative paths using AbsolutePath + NormalizePath. Calls FixFilePath before resolution (critical on Linux where backslash is a valid filename character). Returns path unchanged when CurrentThreadWorkingDirectory is null (non-mt mode) or path is already rooted.

src/Build/Evaluation/Expander.cs

• Add IsFileOrDirectoryPathArgument(string methodName, int argIndex) to identify which arguments are file/directory paths (arg0=always, arg1=Copy/Move/Replace, arg2=Replace).
• Add path resolution in the Function<T>.Execute() arg assembly loop for System.IO.File and System.IO.Directory receiver types, after FixFilePath and before UnescapeAll.
• Fix pre-existing bug: Type comparisons used typeof(Directory) which resolves to Microsoft.IO.Directory on net472 due to FEATURE_MSIOREDIST alias, but _receiverType from AvailableStaticMethods is always System.IO.Directory. Changed to fully-qualified typeof(System.IO.Directory) / typeof(System.IO.Path).

src/Build.UnitTests/Evaluation/Expander_Tests.cs

• Add 38 unit tests across 6 categories:
  • A: Default-allowed File methods (ReadAllText, Exists, GetAttributes, GetCreationTime, GetLastAccessTime, GetLastWriteTime)
  • A: Default-allowed Directory methods (Exists, GetDirectories, GetFiles, GetLastAccessTime, GetLastWriteTime, GetParent)
  • A+: Extended methods under MSBUILDENABLEALLPROPERTYFUNCTIONS=1 (File.Copy, File.Move, File.Delete, File.*Utc, Directory.CreateDirectory, Directory.Delete, Directory.Move)
  • B: Regular mode (no thread working dir) — verifies zero behavior change
  • C/D: Absolute path passthrough and multi-path methods (Copy, Move)
  • E/F: Parent traversal (../) and backslash parent traversal (..\\)

Design Notes

• The fix is in the arg assembly loop, before both WellKnownFunctions and InvokeMember, so it covers all File/Directory methods generically.
• Item functions share the same Function<T>.Execute() codepath, so they're covered automatically.
• The guard string.IsNullOrEmpty(CurrentThreadWorkingDirectory) ensures zero behavior change in non-mt modes (multi-process, single-threaded).
• Drive-relative paths (C:file.txt) are a known limitation — Path.Combine ignores the base when the second argument has a drive letter.

Fixes #13237

[Copilot]

Pull request overview

Fixes MSBuild property function evaluation in multi-threaded (-mt) builds by resolving relative path arguments for System.IO.File/System.IO.Directory against MSBuild’s thread-local working directory rather than the process-global Environment.CurrentDirectory, aligning behavior with existing Path.GetFullPath interception.

Changes:

• Added FileUtilities.MakeFullPathFromThreadWorkingDirectory to resolve relative paths using the thread-local working directory.
• Updated Expander.Function<T>.Execute() to apply thread-local relative-path resolution for System.IO.File/System.IO.Directory path arguments and fixed receiver type comparisons to use System.IO.* explicitly.
• Added extensive unit tests validating correct resolution behavior (including .. traversal and backslash normalization cases).

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 5 comments.

File	Description
src/Shared/FileUtilities.cs	Introduces helper to resolve relative paths against CurrentThreadWorkingDirectory.
src/Build/Evaluation/Expander.cs	Applies the helper during property function argument assembly and corrects System.IO.* type comparisons.
src/Build.UnitTests/Evaluation/Expander_Tests.cs	Adds coverage for relative/absolute path behavior across File/Directory APIs in -mt and non--mt modes.

[Copilot]

In the System.IO.File/System.IO.Directory path-argument case, argumentValue is already passed through FrameworkFileUtilities.FixFilePath immediately above, but MakeFullPathFromThreadWorkingDirectory currently calls FixFilePath again. Consider avoiding double-normalization here (e.g., have the helper assume fixed input, or only call the helper and do FixFilePath once) to keep property function expansion as cheap as possible.

[Copilot]

This helper manually saves/restores Environment.CurrentDirectory and FileUtilities.CurrentThreadWorkingDirectory. In this repo, tests are expected to use TestEnvironment to manage state and avoid manual try/finally restore blocks (e.g., use env.SetCurrentDirectory(...) for the working directory). Refactoring this helper to leverage TestEnvironment will make the tests less error-prone and consistent with the test infrastructure.

[Copilot]

New tests here create the test environment via TestEnvironment.Create() without wiring xUnit's ITestOutputHelper. The repository guidance is to inject ITestOutputHelper into the test class and pass it to TestEnvironment.Create(_output) so failures include diagnostic output in CI logs.