Fix VSTHRD103 missing diagnostic for sync extension methods with async alternatives in the same static class by Copilot · Pull Request #1569 · microsoft/vs-threading

Copilot · 2026-04-12T13:15:00Z

VSTHRD103 failed to flag synchronous extension method calls from async methods when the *Async counterpart was defined in the same static class (e.g., exec.GetOutput() with ExecutableExtensions.GetOutputAsync(this IExecutable) in scope).

Root cause

AnalyzeInvocation called LookupSymbols(container: methodSymbol.ContainingType, ...) to find async alternatives. For reduced extension methods (instance-syntax calls like exec.GetOutput()), ContainingType is the declaring static class (e.g., ExecutableExtensions). LookupSymbols with a static class as container returns nothing useful — it looks for instance-accessible members, but static classes have no instances and their extension methods are scoped to other receiver types.

Fix

VSTHRD103UseAsyncOptionAnalyzer.cs — When methodSymbol.ReducedFrom is non-null (reduced extension method), use reducedFrom.Parameters[0].Type (the receiver type, e.g., IExecutable) as the LookupSymbols container instead of ContainingType. With includeReducedExtensionMethods: true, this correctly finds extension methods applicable to the receiver type across all in-scope static classes.
VSTHRD103UseAsyncOptionAnalyzerTests.cs — Added SyncExtensionMethodWhereAsyncAlternativeExistsInSameStaticClassGeneratesWarning covering the repro scenario from the issue, including code fix verification.

// Before fix: no diagnostic on exec.GetOutput()
// After fix: VSTHRD103 flags GetOutput, code fix produces:
string result = await exec.GetOutputAsync();

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… exists in same static class Agent-Logs-Url: https://github.com/microsoft/vs-threading/sessions/d0908deb-1f03-4a2b-8c97-4c4530598e07 Co-authored-by: drewnoakes <350947+drewnoakes@users.noreply.github.com>

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Pull request overview

Fixes a gap in VSTHRD103 where synchronous reduced extension method invocations (instance-syntax) were not producing diagnostics when an *Async alternative existed as an extension method in the same (or any in-scope) static class.

Changes:

Updates VSTHRD103’s async-alternative lookup to use the reduced extension method’s receiver type as the LookupSymbols container (instead of the declaring static class).
Adds a regression test covering the scenario where both sync/async extension methods live in the same static class and the sync one is invoked via instance syntax.
Verifies the code fix produces await receiver.MethodAsync() as expected.

Reviewed changes

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

File	Description
src/Microsoft.VisualStudio.Threading.Analyzers.CSharp/VSTHRD103UseAsyncOptionAnalyzer.cs	Adjusts symbol lookup to correctly find async alternatives for reduced extension method invocations.
test/Microsoft.VisualStudio.Threading.Analyzers.Tests/VSTHRD103UseAsyncOptionAnalyzerTests.cs	Adds a regression test + code-fix verification for the same-static-class extension method repro.

….23 (#3704) Updated [Microsoft.VisualStudio.Threading.Analyzers](https://github.com/microsoft/vs-threading) from 17.14.15 to 18.7.23. <details> <summary>Release notes</summary> _Sourced from [Microsoft.VisualStudio.Threading.Analyzers's releases](https://github.com/microsoft/vs-threading/releases)._ ## 18.7.23 ## What's Changed ### Fixes * Fix `CancellationToken.Combine` with 3+ cancelable tokens by @AArnott in microsoft/vs-threading#1443 * Fix VSTHRD110 firing in Expression-valued scenarios by @AArnott with @Copilot in microsoft/vs-threading#1467 * Fix super set for VSTHRD103 by @AArnott in microsoft/vs-threading#1545 * Fix VSTHRD114 not firing for null in ternary conditional expressions by @AArnott with @Copilot in microsoft/vs-threading#1548 * Disable VSTHRD010 in AppWithoutMainThread.editorconfig by @ArturDorochowicz in microsoft/vs-threading#1562 * Fix VSTHRD103 missing diagnostic for sync extension methods with async alternatives in the same static class by @drewnoakes with @Copilot in microsoft/vs-threading#1569 ### Enhancements * Add `JoinableTaskFactory.DisableProcessing()` by @AArnott in microsoft/vs-threading#1576 * Add `NoMessagePumpSyncContext..ctor(SynchronizationContext)` for Post/Send behaviors by @AArnott in microsoft/vs-threading#1578 * Add trim and NativeAOT safety attributes by @AArnott in microsoft/vs-threading#1471 * Add `IPendingExecutionRequestState` interface to expose completion state of `SingleExecuteProtector` by @lifengl in microsoft/vs-threading#1447 * Add AdditionalFiles support to VSTHRD103 analyzer for excluding specific APIs by @AArnott with @Copilot in microsoft/vs-threading#1465 * Document InvalidOperationException for AsyncReaderWriterLock acquisition methods by @AArnott with @Copilot in microsoft/vs-threading#1466 * Allow library code to detect the JoinableTaskContext is not associated with Main thread by @lifengl in microsoft/vs-threading#1477 * remove NotifyOfCrossThreadDependency call inside get_NoMessagePumpSynchronizationContext by @lifengl in microsoft/vs-threading#1486 * reduce overhead when running in no main thread mode by @lifengl in microsoft/vs-threading#1502 * Join tasks waited by JoinableTaskCollection.JoinUntilEmpty in dumpasync result by @lifengl in microsoft/vs-threading#1538 * Remove slow regex from threading analyzers by @AArnott in microsoft/vs-threading#1547 ## New Contributors * @jgrosic made their first contribution in microsoft/vs-threading#1485 * @AbhitejJohn made their first contribution in microsoft/vs-threading#1533 * @ArturDorochowicz made their first contribution in microsoft/vs-threading#1562 * @microsoft-github-policy-service[bot] made their first contribution in microsoft/vs-threading#1587 **Full Changelog**: microsoft/vs-threading@v17.14.15...v18.7.23 Commits viewable in [compare view](microsoft/vs-threading@v17.14.15...v18.7.23). </details> [![Dependabot compatibility score](https://dependabot-badges.githubapp.com/badges/compatibility_score?dependency-name=Microsoft.VisualStudio.Threading.Analyzers&package-manager=nuget&previous-version=17.14.15&new-version=18.7.23)](https://docs.github.com/en/github/managing-security-vulnerabilities/about-dependabot-security-updates#about-compatibility-scores) Dependabot will resolve any conflicts with this PR as long as you don't alter it yourself. You can also trigger a rebase manually by commenting `@dependabot rebase`. [//]: # (dependabot-automerge-start) [//]: # (dependabot-automerge-end) --- <details> <summary>Dependabot commands and options</summary> <br /> You can trigger Dependabot actions by commenting on this PR: - `@dependabot rebase` will rebase this PR - `@dependabot recreate` will recreate this PR, overwriting any edits that have been made to it - `@dependabot show <dependency name> ignore conditions` will show all of the ignore conditions of the specified dependency - `@dependabot ignore this major version` will close this PR and stop Dependabot creating any more for this major version (unless you reopen the PR or upgrade to it yourself) - `@dependabot ignore this minor version` will close this PR and stop Dependabot creating any more for this minor version (unless you reopen the PR or upgrade to it yourself) - `@dependabot ignore this dependency` will close this PR and stop Dependabot creating any more for this dependency (unless you reopen the PR or upgrade to it yourself) </details> Signed-off-by: dependabot[bot] <support@github.com> Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Initial plan

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Copilot AI assigned Copilot and Drew Noakes (drewnoakes) Apr 12, 2026

Copilot started work on behalf of Drew Noakes (drewnoakes) April 12, 2026 13:15 View session

Copilot AI linked an issue Apr 12, 2026 that may be closed by this pull request

VSTHRD103 does not flag sync extension method when async alternative exists in the same static class #1568

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Copilot AI and others added 2 commits April 12, 2026 13:29

Fix VSTHRD103 to detect sync extension methods when async alternative…

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… exists in same static class Agent-Logs-Url: https://github.com/microsoft/vs-threading/sessions/d0908deb-1f03-4a2b-8c97-4c4530598e07 Co-authored-by: drewnoakes <350947+drewnoakes@users.noreply.github.com>

Revert accidental nuget.config change (local package source for testi…

3f6ea70

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Copilot AI changed the title ~~[WIP] Fix VSTHRD103 diagnostic for sync extension method calls~~ Fix VSTHRD103 missing diagnostic for sync extension methods with async alternatives in the same static class Apr 12, 2026

Copilot finished work on behalf of Drew Noakes (drewnoakes) April 12, 2026 13:33

Copilot AI requested a review from Drew Noakes (drewnoakes) April 12, 2026 13:33

Drew Noakes (drewnoakes) marked this pull request as ready for review April 13, 2026 09:10

Copilot AI review requested due to automatic review settings April 13, 2026 09:10

Copilot started reviewing on behalf of Drew Noakes (drewnoakes) April 13, 2026 09:11 View session

Copilot AI reviewed Apr 13, 2026

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Andrew Arnott (AArnott) approved these changes Apr 25, 2026

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Andrew Arnott (AArnott) merged commit ea0435c into main Apr 25, 2026
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Andrew Arnott (AArnott) deleted the copilot/fix-vsthrd103-diagnostic-issue branch April 25, 2026 17:51

dependabot Bot mentioned this pull request Aug 30, 2026

Bump Microsoft.VisualStudio.Threading from 17.12.19 to 18.7.23 OffroadOps/Hatch#42

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Fix VSTHRD103 missing diagnostic for sync extension methods with async alternatives in the same static class - #1569

Fix VSTHRD103 missing diagnostic for sync extension methods with async alternatives in the same static class#1569
Andrew Arnott (AArnott) merged 3 commits into
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Copilot AI commented Apr 12, 2026 •

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