VSTHRD003 to allow returning foreign tasks from lambda expressions

microsoft · Nov 16, 2023 · 350dc7f · 350dc7f
1 parent 8fae01d
commit 350dc7f
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Showing 2 changed files with 48 additions and 8 deletions.
diff --git a/src/Microsoft.VisualStudio.Threading.Analyzers.CSharp/VSTHRD003UseJtfRunAsyncAnalyzer.cs b/src/Microsoft.VisualStudio.Threading.Analyzers.CSharp/VSTHRD003UseJtfRunAsyncAnalyzer.cs
@@ -195,16 +195,30 @@ private void AnalyzeAwaitExpression(SyntaxNodeAnalysisContext context)
                     }
 
                     // Do not report a warning if the task is a member of an object that was created in this method.
-                    if (memberAccessExpression.Expression is IdentifierNameSyntax identifier &&
-                        semanticModel.GetSymbolInfo(identifier, cancellationToken).Symbol is ILocalSymbol local)
+                    if (memberAccessExpression.Expression is IdentifierNameSyntax identifier)
                     {
-                        // Search for assignments to the local and see if it was to a new object or the result of an invocation.
-                        containingFunc ??= CSharpUtils.GetContainingFunction(focusedExpression);
-                        if (containingFunc.Value.BlockOrExpression is not null &&
-                            CSharpUtils.FindAssignedValuesWithin(containingFunc.Value.BlockOrExpression, semanticModel, local, cancellationToken).Any(
-                                v => v is ObjectCreationExpressionSyntax or ImplicitObjectCreationExpressionSyntax or InvocationExpressionSyntax))
+                        ISymbol? symbol = semanticModel.GetSymbolInfo(identifier, cancellationToken).Symbol;
+                        switch (symbol)
                         {
-                            return null;
+                            case ILocalSymbol local:
+                                // Search for assignments to the local and see if it was to a new object or the result of an invocation.
+                                containingFunc ??= CSharpUtils.GetContainingFunction(focusedExpression);
+                                if (containingFunc.Value.BlockOrExpression is not null &&
+                                    CSharpUtils.FindAssignedValuesWithin(containingFunc.Value.BlockOrExpression, semanticModel, local, cancellationToken).Any(
+                                        v => v is ObjectCreationExpressionSyntax or ImplicitObjectCreationExpressionSyntax or InvocationExpressionSyntax))
+                                {
+                                    return null;
+                                }
+
+                                break;
+                            case IParameterSymbol parameter:
+                                // We allow returning members of a parameter in a lambda, to support `.Select(x => x.Completion)` syntax.
+                                if (parameter.ContainingSymbol is IMethodSymbol method && method.MethodKind == MethodKind.AnonymousFunction)
+                                {
+                                    return null;
+                                }
+
+                                break;
                         }
                     }
                 }

diff --git a/.../Microsoft.VisualStudio.Threading.Analyzers.Tests/VSTHRD003UseJtfRunAsyncAnalyzerTests.cs b/.../Microsoft.VisualStudio.Threading.Analyzers.Tests/VSTHRD003UseJtfRunAsyncAnalyzerTests.cs
@@ -1402,6 +1402,32 @@ async Task GetTask()
         await CSVerify.VerifyAnalyzerAsync(test);
     }
 
+    [Fact]
+    public async Task DoNotReportWarningWhenReturningTaskFromLambdaArgument()
+    {
+        var test = """
+            using System.Linq;
+            using System.Threading.Tasks;
+
+            class JsonRpc
+            {
+                internal static JsonRpc Attach() => throw new System.NotImplementedException();
+
+                internal Task Completion { get; }
+            }
+
+            class Tests
+            {
+                static async Task ListenAndWait()
+                {
+                    JsonRpc[] rpcs = new [] { JsonRpc.Attach(), JsonRpc.Attach() };
+                    await Task.WhenAll(rpcs.Select(r => r.Completion));
+                }
+            }
+            """;
+        await CSVerify.VerifyAnalyzerAsync(test);
+    }
+
     private DiagnosticResult CreateDiagnostic(int line, int column, int length) =>
         CSVerify.Diagnostic().WithSpan(line, column, line, column + length);
 }