Migrate ReadStaticWebAssetsManifestFile

[AlesProkop]

Fixes dotnet/msbuild#14060

Context

Migrates ReadStaticWebAssetsManifestFile to support MSBuild multithreaded task execution. The task reads the static web assets manifest from disk, so it needs to avoid resolving relative paths against process-wide current directory state.

Changes Made

• Added [MSBuildMultiThreadableTask] to ReadStaticWebAssetsManifestFile.
• Implemented IMultiThreadableTask and initialized TaskEnvironment with TaskEnvironment.Fallback.
• Absolutized ManifestPath with TaskEnvironment.GetAbsolutePath() before file system access.
• Preserved existing missing-manifest behavior and error text for valid missing paths and empty/invalid paths.
• Added a focused regression test for empty manifest path handling.

Testing

• Built D:\msbuild\src\ThreadSafeTaskAnalyzer\ThreadSafeTaskAnalyzer.csproj.
• Ran the thread-safe task analyzer against src\StaticWebAssetsSdk\Tasks\Microsoft.NET.Sdk.StaticWebAssets.Tasks.csproj.
  • No analyzer diagnostics for ReadStaticWebAssetsManifestFile.
  • The project still reports unrelated diagnostics in other task files.
• Built src\StaticWebAssetsSdk\Tasks\Microsoft.NET.Sdk.StaticWebAssets.Tasks.csproj.
• Ran focused tests:
  • Microsoft.NET.Sdk.StaticWebAssets.Tests.ReadStaticWebAssetsManifestFileTest
  • Result: 8 passed, 0 failed.

[Copilot]

Pull request overview

Migrates ReadStaticWebAssetsManifestFile to be safe for MSBuild multi-threaded task execution by eliminating reliance on process-wide current directory when resolving the manifest path.

Changes:

• Marked ReadStaticWebAssetsManifestFile as [MSBuildMultiThreadableTask] and implemented IMultiThreadableTask with a TaskEnvironment fallback.
• Resolved ManifestPath to an absolute path via TaskEnvironment.GetAbsolutePath() before doing file-system reads.
• Added a regression test ensuring empty ManifestPath continues to produce the existing “not found” error behavior instead of throwing.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
src/StaticWebAssetsSdk/Tasks/ReadStaticWebAssetsManifestFile.cs	Makes the task MSBuild-multithread friendly by resolving manifest paths via TaskEnvironment and using the absolute path for file IO.
test/Microsoft.NET.Sdk.StaticWebAssets.Tests/StaticWebAssets/ReadStaticWebAssetsManifestFileTest.cs	Adds a focused regression test for empty manifest path handling to ensure behavior remains stable post-migration.

[AlesProkop]

Reviewed this as an MSBuild multithreaded-task migration and I don't see actionable issues.

The task is marked [MSBuildMultiThreadableTask], implements IMultiThreadableTask with TaskEnvironment.Fallback, absolutizes ManifestPath before the file-system calls, keeps user-facing messages on the original ManifestPath, and does not leak absolute paths into outputs. The empty-path test covers the new GetAbsolutePath ArgumentException path. No review comments from me.

[jankratochvilcz]

Left a few comments, thanks for the PR!

[jankratochvilcz]

🚢 it!