Fix VSTHRD003 crash on conversion operators

src/Microsoft.VisualStudio.Threading.Analyzers.CSharp/CSharpUtils.cs

@@ -70,7 +70,7 @@ public static ContainingFunctionData GetContainingFunction(CSharpSyntaxNode? syn
                 {
                     BlockSyntax block => accessor.WithBody(block),
                     ArrowExpressionClauseSyntax expression => accessor.WithExpressionBody(expression),
-                    _ => throw new NotSupportedException(),
+                    _ => throw new NotSupportedException($"Body syntax type '{newBody.GetType().FullName}' is not supported."),
                 };
                 return new ContainingFunctionData(accessor, false, SyntaxFactory.ParameterList(), accessor.Body, bodyReplacement);
             }
@@ -83,27 +83,33 @@ public static ContainingFunctionData GetContainingFunction(CSharpSyntaxNode? syn
                     {
                         ArrowExpressionClauseSyntax expr => m.WithExpressionBody(expr),
                         BlockSyntax block => m.WithBody(block),
-                        _ => throw new NotSupportedException(),
+                        _ => throw new NotSupportedException($"Body syntax type '{newBody.GetType().FullName}' is not supported."),
                     },
                     ConstructorDeclarationSyntax c => (CSharpSyntaxNode newBody) => newBody switch
                     {
                         ArrowExpressionClauseSyntax expr => c.WithExpressionBody(expr),
                         BlockSyntax block => c.WithBody(block),
-                        _ => throw new NotSupportedException(),
+                        _ => throw new NotSupportedException($"Body syntax type '{newBody.GetType().FullName}' is not supported."),
                     },
                     OperatorDeclarationSyntax o => (CSharpSyntaxNode newBody) => newBody switch
                     {
                         ArrowExpressionClauseSyntax expr => o.WithExpressionBody(expr),
                         BlockSyntax block => o.WithBody(block),
-                        _ => throw new NotSupportedException(),
+                        _ => throw new NotSupportedException($"Body syntax type '{newBody.GetType().FullName}' is not supported."),
+                    },
+                    ConversionOperatorDeclarationSyntax c => (CSharpSyntaxNode newBody) => newBody switch
+                    {
+                        ArrowExpressionClauseSyntax expr => c.WithExpressionBody(expr),
+                        BlockSyntax block => c.WithBody(block),
+                        _ => throw new NotSupportedException($"Body syntax type '{newBody.GetType().FullName}' is not supported."),
                     },
                     DestructorDeclarationSyntax d => (CSharpSyntaxNode newBody) => newBody switch
                     {
                         ArrowExpressionClauseSyntax expr => d.WithExpressionBody(expr),
                         BlockSyntax block => d.WithBody(block),
-                        _ => throw new NotSupportedException(),
+                        _ => throw new NotSupportedException($"Body syntax type '{newBody.GetType().FullName}' is not supported."),
                     },
-                    _ => throw new NotSupportedException(),
+                    _ => throw new NotSupportedException($"Method syntax type '{method.GetType().FullName}' is not supported."),
                 };
                 return new ContainingFunctionData(method, method.Modifiers.Any(SyntaxKind.AsyncKeyword), method.ParameterList, method.Body, bodyReplacement);
             }

test/Microsoft.VisualStudio.Threading.Analyzers.Tests/VSTHRD003UseJtfRunAsyncAnalyzerTests.cs

@@ -158,6 +158,24 @@ public Task GetTask()
         await CSVerify.VerifyAnalyzerAsync(test, expected);
     }
 
+    [Fact]
+    public async Task ReturnStatementInConversionOperatorProducesNoDiagnostic()
+    {
+        string test = """
+            readonly struct Wrapper
+            {
+                private readonly byte value;
+
+                public static implicit operator byte(Wrapper value)
+                {
+                    return value.value;
+                }
+            }
+            """;
+
+        await CSVerify.VerifyAnalyzerAsync(test);
+    }
+
     [Fact]
     public async Task ReportWarningWhenTaskIsReturnedDirectlyFromMethodViaExpressionBody()
     {