Thread-safe task analyzer (without IL decompiler) by JanProvaznik · Pull Request #13444 · dotnet/msbuild

JanProvaznik · 2026-03-24T10:03:17Z

Thread-Safe Task Analyzer

Adds a Roslyn analyzer that detects unsafe API usage in MSBuild task implementations, guiding task authors toward thread-safe patterns required for multithreaded task execution (IMultiThreadableTask).

Diagnostic Rules

ID	Default Severity	Title
MSBuildTask0001	Error	API is never safe in MSBuild tasks (Console.*, Environment.Exit, ThreadPool, etc.)
MSBuildTask0002	Warning / Info ¹	API requires TaskEnvironment alternative
MSBuildTask0003	Warning / Info ¹	File system API requires absolute path
MSBuildTask0004	Warning / Info ¹	API may cause issues (Assembly.Load, Activator, etc.)
MSBuildTask0005	Warning / Info ¹	Transitive unsafe API in call chain (source-level BFS)

¹ Warning for IMultiThreadableTask / [MSBuildMultiThreadableTask], Info for plain ITask. Users can configure via .editorconfig.

What's included

Core analyzer (MultiThreadableTaskAnalyzer): Per-type scoped analysis via RegisterSymbolStartAction
Transitive analyzer (TransitiveCallChainAnalyzer): Source-level BFS call graph traces unsafe APIs through helper methods
Code fix provider: Auto-fixes for MSBuildTask0002 (TaskEnvironment replacements) and MSBuildTask0003 (GetAbsolutePath wrapping)
Shared helpers (SharedAnalyzerHelpers): Deduplicated path safety analysis and banned API resolution
109 unit tests passing

Build integration

Added to MSBuild.slnx
/p:BuildAnalyzer=true enables analyzer on Tasks.csproj
Produces 56 warnings on Tasks project (34 env + 12 path + 10 transitive), 0 false positives

Safe pattern recognition (zero false positives verified)

ITaskItem.GetMetadata("FullPath")
Path.Combine(absolutePath, ...)
Path.GetDirectoryName(absolutePath)
AbsolutePath type (implicit conversion)
File.WriteAllText(path, contents) — only path param flagged

What's NOT included (preserved in `threadsafe-analyzer` branch)

IL decompiler (ILCallGraphExtender.cs) — 1,011 lines of raw IL byte parsing with 6 verified opcode bugs
Demo project (~1,600 lines)
Cross-assembly IL tests (~870 lines)

Testing

Stress-tested on MSBuild Tasks project, external task libraries, and SDK-style task patterns
Zero false positives across all test scenarios

Adds a Roslyn analyzer for MSBuild task thread safety with: Core analyzer (MultiThreadableTaskAnalyzer): - MSBuildTask0001: Critical APIs banned in all tasks (Console.*, Environment.Exit) - MSBuildTask0002: APIs requiring TaskEnvironment alternatives - MSBuildTask0003: File APIs requiring absolute paths - MSBuildTask0004: Potentially problematic APIs (Assembly.Load, etc.) Transitive analysis (TransitiveCallChainAnalyzer): - MSBuildTask0005: Source-level BFS call graph traces unsafe APIs through helpers Dual severity: Warning for IMultiThreadableTask, Info for plain ITask. Code fix provider for MSBuildTask0002/0003 with TaskEnvironment replacements. Build integration: - Added to MSBuild.slnx - Tasks.csproj: /p:BuildAnalyzer=true enables analyzer - 109 tests passing Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Removes Microsoft.NET.Test.Sdk, xunit.runner.visualstudio, and other packages that are implicitly referenced by the .NET SDK. These cause NETSDK1023 errors in the repo's SDK (10.0.104) which treats this as an error, not a warning. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Adds a Roslyn analyzer (MSBuildTask0001-0005) that detects unsafe API usage in MSBuild task implementations for multithreaded execution. Analyzer project uses central package management. Test project opts out (ManagePackageVersionsCentrally=false) due to NuGet version conflicts in CodeAnalysis.Testing transitive dependencies. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

JanProvaznik · 2026-03-24T15:33:26Z

Analyzer Findings on MSBuild Tasks (`/p:BuildAnalyzer=true`)

15 unique issues across 6 task files. These are real thread-safety issues to fix in follow-up PRs.

MSBuildTask0002 — TaskEnvironment Replacement Required (10)

File	Line	API	Fix
Copy.cs	118	`Environment.GetEnvironmentVariable("MSBuildCopyParallelCount")`	`TaskEnvironment.GetEnvironmentVariable()`
Copy.cs	123	`Environment.GetEnvironmentVariable("MSBUILDALWAYSRETRY")`	`TaskEnvironment.GetEnvironmentVariable()`
Copy.cs	241	`Environment.GetEnvironmentVariable("MSBUILDALWAYSOVERWRITEREADONLYFILES")`	`TaskEnvironment.GetEnvironmentVariable()`
AssignTargetPath.cs	85	`Path.GetFullPath(item)`	`TaskEnvironment.GetAbsolutePath()`
AssignTargetPath.cs	146	`Path.GetFullPath(rootDir)`	`TaskEnvironment.GetAbsolutePath()`
FindUnderPath.cs	76	`Path.GetFullPath(Path.Value)`	`TaskEnvironment.GetAbsolutePath()`
FindUnderPath.cs	107	`Path.GetFullPath(item.ItemSpec)`	`TaskEnvironment.GetAbsolutePath()`
Unzip.cs	179	`Path.GetFullPath(...)` destination	`TaskEnvironment.GetAbsolutePath()`
Unzip.cs	189	`Path.GetFullPath(...)` zip-slip check	`TaskEnvironment.GetAbsolutePath()`

MSBuildTask0003 — File API Requires Absolute Path (1)

File	Line	API
GetFileHash.cs	148	`File.OpenRead(filePath)` — wrap with `TaskEnvironment.GetAbsolutePath()`

MSBuildTask0005 — Transitive Unsafe API in Call Chain (4)

File	Line	Chain	Unsafe API
Copy.cs	209	`IsMatchingSizeAndTimeStamp → FileState.get_Length → FileDirInfo.ThrowFileInfoException`	`new FileInfo(string)`
Copy.cs	261	`CopyFileWithLogging → FileState.Reset → FileDirInfo..ctor`	`new DirectoryInfo(string)`
Move.cs	92	`Execute → MoveFileWithLogging → NativeMethods.MoveFileEx`	`File.Move`, `File.Delete`, `File.GetAttributes`

Recommended Migration Order

Copy.cs (High) — most-used task, already IMultiThreadableTask
AssignTargetPath.cs (Medium) — 2 Path.GetFullPath calls
FindUnderPath.cs (Medium) — 2 Path.GetFullPath calls
Unzip.cs (Medium) — 2 Path.GetFullPath calls
Move.cs (Low) — transitive, paths typically absolute
GetFileHash.cs (Low) — 1 File.OpenRead, path typically absolute

- All diagnostics are Warning (removed dual Info/Warning severity) - Added WarningsNotAsErrors in Tasks.csproj so analyzer warnings don't break WarnAsError builds while issues are being fixed - Enabled /p:BuildAnalyzer=true in Linux Core Multithreaded Mode CI job - Removed issues.md (posted as PR comment instead) Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Copilot

Pull request overview

This PR adds a new Roslyn analyzer + code fix package to help MSBuild task authors identify (and in some cases automatically migrate away from) APIs that are unsafe under multithreaded task execution (IMultiThreadableTask), including a transitive call-chain analyzer to surface unsafe APIs reached through helper methods.

Changes:

Added ThreadSafeTaskAnalyzer analyzer project (direct API rules + shared helpers + transitive call-chain rule) and integrated it into MSBuild.slnx.
Added a code fix provider for MSBuildTask0002 (TaskEnvironment replacements) and MSBuildTask0003 (absolute path wrapping).
Added a new analyzer test project and enabled running the analyzer on Microsoft.Build.Tasks when /p:BuildAnalyzer=true (including CI).

Reviewed changes

Copilot reviewed 21 out of 21 changed files in this pull request and generated 10 comments.

Show a summary per file

File	Description
src/ThreadSafeTaskAnalyzer/TransitiveCallChainAnalyzer.cs	Implements compilation-wide call graph scan + BFS to report transitive unsafe API usage (MSBuildTask0005).
src/ThreadSafeTaskAnalyzer/SharedAnalyzerHelpers.cs	Shared banned API lookup + path-argument safety detection helpers.
src/ThreadSafeTaskAnalyzer/MultiThreadableTaskAnalyzer.cs	Direct per-type analyzer for MSBuildTask0001–0004, scoped via `RegisterSymbolStartAction`.
src/ThreadSafeTaskAnalyzer/MultiThreadableTaskCodeFixProvider.cs	Code fixes for MSBuildTask0002/0003.
src/ThreadSafeTaskAnalyzer/BannedApiDefinitions.cs	Defines banned API sets resolved via documentation IDs.
src/ThreadSafeTaskAnalyzer/DiagnosticDescriptors.cs	Defines diagnostic descriptors for MSBuildTask0001–0005.
src/ThreadSafeTaskAnalyzer/DiagnosticIds.cs	Adds public IDs for the analyzer rules.
src/ThreadSafeTaskAnalyzer/README.md	Documents rule set, scope, fixes, usage, and architecture.
src/ThreadSafeTaskAnalyzer/AnalyzerReleases.Unshipped.md	Tracks new analyzer rules for Roslyn release tracking.
src/ThreadSafeTaskAnalyzer/AnalyzerReleases.Shipped.md	Initializes shipped release tracking file.
src/ThreadSafeTaskAnalyzer/ThreadSafeTaskAnalyzer.csproj	New analyzer project definition + Roslyn package references.
src/ThreadSafeTaskAnalyzer.Tests/TestHelpers.cs	Test harness that compiles sources with framework stubs and runs analyzers.
src/ThreadSafeTaskAnalyzer.Tests/MultiThreadableTaskAnalyzerTests.cs	Large unit test suite validating direct analyzer behavior and safe patterns.
src/ThreadSafeTaskAnalyzer.Tests/TransitiveCallChainAnalyzerTests.cs	Unit tests validating MSBuildTask0005 transitive detection and chain formatting.
src/ThreadSafeTaskAnalyzer.Tests/MultiThreadableTaskCodeFixProviderTests.cs	Code-fix transformation tests via `CSharpCodeFixTest`.
src/ThreadSafeTaskAnalyzer.Tests/WriteAllTextDetailedTest.cs	Regression-style test validating path diagnostic count for `WriteAllText`.
src/ThreadSafeTaskAnalyzer.Tests/ThreadSafeTaskAnalyzer.Tests.csproj	New test project configuration and package references.
src/Tasks/Microsoft.Build.Tasks.csproj	Adds conditional analyzer reference (BuildAnalyzer) + relaxes analyzer IDs from WarnAsError.
eng/dependabot/Directory.Packages.props	Adds Roslyn authoring package versions for central management.
MSBuild.slnx	Includes the new analyzer and analyzer test projects in the main solution.
.vsts-dotnet-ci.yml	Enables `/p:BuildAnalyzer=true` in the bootstrapped `-mt` CI leg.

src/ThreadSafeTaskAnalyzer/TransitiveCallChainAnalyzer.cs

src/ThreadSafeTaskAnalyzer/ThreadSafeTaskAnalyzer.csproj

src/ThreadSafeTaskAnalyzer/TransitiveCallChainAnalyzer.cs

src/ThreadSafeTaskAnalyzer/ThreadSafeTaskAnalyzer.csproj

src/Tasks/Microsoft.Build.Tasks.csproj

src/ThreadSafeTaskAnalyzer/README.md

src/ThreadSafeTaskAnalyzer/MultiThreadableTaskCodeFixProvider.cs

src/ThreadSafeTaskAnalyzer/TransitiveCallChainAnalyzer.cs

src/ThreadSafeTaskAnalyzer/README.md

src/ThreadSafeTaskAnalyzer/MultiThreadableTaskCodeFixProvider.cs

CI fixes: - SA1133: Split combined attributes in CodeFixProvider - SA1111: Move closing parens to last parameter lines - SA1508: Remove blank line before closing brace Review fixes: - Remove pinned LangVersion 12.0 (repo default is latest) - Update RS2001 suppression comment - Remove MSBuildTask0001 from WarningsNotAsErrors (it's Error, not Warning) - Make FindTaskTypes recursive for deeply nested types - Fix README: remove dual-severity claims, clarify performance notes Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

AR-May

Looks good to go. Most my comments are just suggestions.

src/ThreadSafeTaskAnalyzer/README.md

src/ThreadSafeTaskAnalyzer/AnalyzerReleases.Shipped.md

src/ThreadSafeTaskAnalyzer/DiagnosticDescriptors.cs

src/ThreadSafeTaskAnalyzer/TransitiveCallChainAnalyzer.cs

src/ThreadSafeTaskAnalyzer.Tests/TransitiveCallChainAnalyzerTests.cs

src/ThreadSafeTaskAnalyzer/MultiThreadableTaskAnalyzer.cs

- Clarify [MSBuildMultiThreadableTaskAnalyzed] attribute purpose in README - Simplify AnalyzerReleases.Shipped.md format - Improve MSBuildTask0003 message to mention shared working directory - Extract shared constants to WellKnownTypeNames.cs - Add doc comment explaining MaxCallChainDepth purpose - Deduplicate scope option reading into SharedAnalyzerHelpers - Convert 3 similar transitive tests to Theory with InlineData - Add scope option tests (multithreadable_only vs all) - Add TestAnalyzerConfigOptionsProvider for scope testing Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

…ng period Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

## Thread-Safe Task Analyzer Adds a Roslyn analyzer that detects unsafe API usage in MSBuild task implementations, guiding task authors toward thread-safe patterns required for multithreaded task execution (`IMultiThreadableTask`). ### Diagnostic Rules | ID | Default Severity | Title | |----|-----------------|-------| | **MSBuildTask0001** | Error | API is never safe in MSBuild tasks (Console.*, Environment.Exit, ThreadPool, etc.) | | **MSBuildTask0002** | Warning / Info ¹ | API requires TaskEnvironment alternative | | **MSBuildTask0003** | Warning / Info ¹ | File system API requires absolute path | | **MSBuildTask0004** | Warning / Info ¹ | API may cause issues (Assembly.Load, Activator, etc.) | | **MSBuildTask0005** | Warning / Info ¹ | Transitive unsafe API in call chain (source-level BFS) | ¹ Warning for `IMultiThreadableTask` / `[MSBuildMultiThreadableTask]`, Info for plain `ITask`. Users can configure via `.editorconfig`. ### What's included - **Core analyzer** (`MultiThreadableTaskAnalyzer`): Per-type scoped analysis via `RegisterSymbolStartAction` - **Transitive analyzer** (`TransitiveCallChainAnalyzer`): Source-level BFS call graph traces unsafe APIs through helper methods - **Code fix provider**: Auto-fixes for MSBuildTask0002 (TaskEnvironment replacements) and MSBuildTask0003 (`GetAbsolutePath` wrapping) - **Shared helpers** (`SharedAnalyzerHelpers`): Deduplicated path safety analysis and banned API resolution - **109 unit tests** passing ### Build integration - Added to `MSBuild.slnx` - `/p:BuildAnalyzer=true` enables analyzer on Tasks.csproj - Produces 56 warnings on Tasks project (34 env + 12 path + 10 transitive), 0 false positives ### Safe pattern recognition (zero false positives verified) - `ITaskItem.GetMetadata("FullPath")` - `Path.Combine(absolutePath, ...)` - `Path.GetDirectoryName(absolutePath)` - `AbsolutePath` type (implicit conversion) - `File.WriteAllText(path, contents)` — only path param flagged ### What's NOT included (preserved in `threadsafe-analyzer` branch) - IL decompiler (`ILCallGraphExtender.cs`) — 1,011 lines of raw IL byte parsing with 6 verified opcode bugs - Demo project (~1,600 lines) - Cross-assembly IL tests (~870 lines) ### Testing - Stress-tested on MSBuild Tasks project, external task libraries, and SDK-style task patterns - Zero false positives across all test scenarios --------- Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

JanProvaznik force-pushed the threadsafe-analyzer-v2 branch from 39edd10 to 70b47ee Compare March 24, 2026 11:03

JanProvaznik force-pushed the threadsafe-analyzer-v2 branch 2 times, most recently from 6842561 to 460144b Compare March 24, 2026 15:32

JanProvaznik force-pushed the threadsafe-analyzer-v2 branch from 460144b to 3feb591 Compare March 24, 2026 15:32

JanProvaznik marked this pull request as ready for review March 24, 2026 15:48

JanProvaznik requested a review from a team as a code owner March 24, 2026 15:48

Copilot AI review requested due to automatic review settings March 24, 2026 15:48

Copilot started reviewing on behalf of JanProvaznik March 24, 2026 15:49 View session

Copilot AI reviewed Mar 24, 2026

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JanProvaznik self-assigned this Mar 25, 2026

AR-May approved these changes Mar 27, 2026

View reviewed changes

JanProvaznik and others added 2 commits March 27, 2026 15:45

Fix RS1032: diagnostic message must be single sentence without traili…

a7cf8c6

…ng period Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

JanProvaznik merged commit ee7d635 into dotnet:main Mar 30, 2026
10 checks passed

JanProvaznik mentioned this pull request Mar 30, 2026

Add analyzer support for the new Tasks #11833

Closed

This was referenced Mar 30, 2026

[release/10.0.3xx] Source code updates from dotnet/msbuild dotnet/dotnet#5740

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[release/11.0.1xx-preview3] Source code updates from dotnet/msbuild dotnet/dotnet#5752

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[main] Source code updates from dotnet/msbuild dotnet/dotnet#5736

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Thread-safe task analyzer (without IL decompiler)#13444

Thread-safe task analyzer (without IL decompiler)#13444
JanProvaznik merged 7 commits intodotnet:mainfrom
JanProvaznik:threadsafe-analyzer-v2

JanProvaznik commented Mar 24, 2026

Uh oh!

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JanProvaznik commented Mar 24, 2026