Fix VSTHRD110 firing in Expression-valued scenarios #1467

Copilot · 2025-06-11T02:45:39Z

Summary

This PR fixes VSTHRD110 analyzer incorrectly firing when Task-valued lambdas are passed to methods expecting Expression<> parameters. In these scenarios, the lambda is converted to an expression tree (data structure) rather than being executed, so no warning should be shown.

Problem

When using libraries like Moq, VSTHRD110 would incorrectly fire on legitimate code:

using Moq;

var mock = new Mock<ILogger>();
mock.Verify(
    x => x.InfoAsync(It.IsAny<string>()), // VSTHRD110 incorrectly fires here
    Times.Never,
    "No Log should have been written");

public interface ILogger
{
    Task InfoAsync(string message);
}

The lambda x => x.InfoAsync(It.IsAny<string>()) is converted to an Expression<Func<ILogger, Task>> for inspection by Moq, not actually executed, so VSTHRD110 should not apply.

Solution

Added detection logic to AbstractVSTHRD110ObserveResultOfAsyncCallsAnalyzer that:

Checks if invocation is within a lambda: Walks up the operation tree to find containing IAnonymousFunctionOperation
Detects Expression<> conversion: Identifies when the lambda is converted to System.Linq.Expressions.Expression<T> via:
- IConversionOperation (direct assignment: Expression<Func<T, Task>> expr = x => x.Method())
- IArgumentOperation (method parameter: SomeMethod(x => x.Method()) where parameter is Expression<>)
Suppresses diagnostic: Skips VSTHRD110 when expression tree conversion is detected

Test Coverage

Added comprehensive test cases covering:

✅ Moq.Verify-like scenarios (mock.Verify(x => x.InfoAsync("test"), Times.Never))
✅ Direct assignment (Expression<Func<T, Task>> expr = x => x.InfoAsync("test"))
✅ Method parameters (SomeMethod(x => x.InfoAsync("test")) where parameter is Expression<>)
✅ Regression test ensuring normal Task calls still trigger VSTHRD110

Edge Cases Handled

Intermediate operations like parentheses between lambda and conversion
Generic Expression<> types with various Func signatures
Other expression tree types in System.Linq.Expressions namespace

Fixes #1167.

Warning

Firewall rules blocked me from connecting to one or more addresses

I tried to connect to the following addresses, but was blocked by firewall rules:

1elvsblobprodwus2177.vsblob.vsassets.io
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Co-authored-by: AArnott <[email protected]>

AArnott · 2025-06-11T03:03:11Z

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Copilot AI assigned Copilot and AArnott Jun 11, 2025

Copilot started work on behalf of AArnott June 11, 2025 02:45 View session

Copilot AI and others added 2 commits June 11, 2025 02:54

Implement fix for VSTHRD110 firing in expression-valued scenarios

19e83e9

Co-authored-by: AArnott <[email protected]>

Enhanced fix for VSTHRD110 with improved detection and additional tests

b54e5a6

Co-authored-by: AArnott <[email protected]>

Copilot AI changed the title ~~[WIP] VSTHRD110 fires in Expression-valued scenarios~~ Fix VSTHRD110 firing in Expression-valued scenarios Jun 11, 2025

Copilot AI requested a review from AArnott June 11, 2025 03:00

Copilot finished work on behalf of AArnott June 11, 2025 03:00

AArnott approved these changes Jun 11, 2025

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AArnott marked this pull request as ready for review June 11, 2025 13:40

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ekoppel approved these changes Jun 11, 2025

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AArnott merged commit b3c2d21 into main Jun 11, 2025
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AArnott deleted the copilot/fix-1167 branch June 11, 2025 15:14

AArnott mentioned this pull request Jun 11, 2025

Agent keeps rolling SDK version backward in global.json as first step copilot-coding-agent/user-feedback#38

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Fix VSTHRD110 firing in Expression-valued scenarios #1467

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Summary

Problem

Solution

Test Coverage

Edge Cases Handled

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