Fix VSTHRD004 mis-fire on NoThrowAwaitable()

Fixes microsoft#1232
AArnott · Oct 23, 2023 · 047a498 · 047a498
1 parent a74e8e8
commit 047a498
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Showing 2 changed files with 35 additions and 4 deletions.
diff --git a/...VisualStudio.Threading.Analyzers/AbstractVSTHRD004AwaitSwitchToMainThreadAsyncAnalyzer.cs b/...VisualStudio.Threading.Analyzers/AbstractVSTHRD004AwaitSwitchToMainThreadAsyncAnalyzer.cs
@@ -45,12 +45,23 @@ private void AnalyzeInvocation(OperationAnalysisContext context)
             methodSymbol.ContainingType.Name == Types.JoinableTaskFactory.TypeName &&
             methodSymbol.ContainingType.BelongsToNamespace(Types.JoinableTaskFactory.Namespace))
         {
-            // This is a call to JTF.SwitchToMainThreadAsync(). Is it being (directly) awaited?
-            if (!(invocation.Parent is IAwaitOperation))
+            // This is a call to JTF.SwitchToMainThreadAsync(). Is it being awaited in some ancestor?
+            for (IOperation? parentOp = invocation.Parent; parentOp is not null; parentOp = parentOp.Parent)
             {
-                Location? location = (this.LanguageUtils.IsolateMethodName(invocation) ?? invocation.Syntax).GetLocation();
-                context.ReportDiagnostic(Diagnostic.Create(Descriptor, location));
+                if (parentOp is IAwaitOperation)
+                {
+                    return;
+                }
+
+                if (parentOp is IExpressionStatementOperation or IReturnOperation)
+                {
+                    // We've reached the top of the statement without finding an await.
+                    break;
+                }
             }
+
+            Location? location = (this.LanguageUtils.IsolateMethodName(invocation) ?? invocation.Syntax).GetLocation();
+            context.ReportDiagnostic(Diagnostic.Create(Descriptor, location));
         }
     }
 }
diff --git a/...ualStudio.Threading.Analyzers.Tests/VSTHRD004AwaitSwitchToMainThreadAsyncAnalyzerTests.cs b/...ualStudio.Threading.Analyzers.Tests/VSTHRD004AwaitSwitchToMainThreadAsyncAnalyzerTests.cs
@@ -104,6 +104,26 @@ async Task FooAsync()
         await CSVerify.VerifyAnalyzerAsync(test);
     }
 
+    [Fact]
+    public async Task AsyncMethodWithAwaitNoThrowAwaitable_ProducesNoDiagnostic()
+    {
+        var test = @"
+using System.Threading.Tasks;
+
+class Test
+{
+    Microsoft.VisualStudio.Threading.JoinableTaskFactory jtf;
+
+    async Task FooAsync()
+    {
+        await jtf.SwitchToMainThreadAsync().NoThrowAwaitable();
+    }
+}
+";
+
+        await CSVerify.VerifyAnalyzerAsync(test);
+    }
+
     [Fact]
     public async Task TaskReturningSyncMethod_ProducesDiagnostic()
     {