Don't mutate LRO operator multiple times (Azure#53304)

Author: JoshLove-msft

eng/packages/http-client-csharp/generator/Azure.Generator/src/Visitors/LroVisitor.cs

@@ -5,6 +5,7 @@
 using System.Collections.Generic;
 using System.Linq;
 using System.Runtime.CompilerServices;
+using System.Text.Json;
 using System.Threading.Tasks;
 using Azure.Core;
 using Azure.Generator.Providers;
@@ -14,6 +15,7 @@
 using Microsoft.TypeSpec.Generator.Input;
 using Microsoft.TypeSpec.Generator.Primitives;
 using Microsoft.TypeSpec.Generator.Providers;
+using Microsoft.TypeSpec.Generator.Snippets;
 using Microsoft.TypeSpec.Generator.Statements;
 using static Microsoft.TypeSpec.Generator.Snippets.Snippet;
 
@@ -57,16 +59,24 @@ private static void UpdateExplicitOperatorMethod(
 
             foreach (var statement in explicitOperator.BodyStatements!)
             {
-                if (statement is ExpressionStatement { Expression: KeywordExpression
-                        { Keyword: "return", Expression: InvokeMethodExpression invokeMethodExpression } })
+                if (statement is ExpressionStatement
+                    {
+                        Expression: KeywordExpression
+                        {
+                            Keyword: "return", Expression: InvokeMethodExpression invokeMethodExpression
+                        }
+                    })
                 {
-                    invokeMethodExpression.Update(
-                        arguments:
-                        [
-                            invokeMethodExpression.Arguments[0]
-                                .Invoke("GetProperty", Literal(resultSegment)),
-                            ..invokeMethodExpression.Arguments.Skip(1)
-                        ]);
+                    if (invokeMethodExpression.Arguments.Count > 0 && invokeMethodExpression.Arguments[0] is ScopedApi<JsonElement>)
+                    {
+                        invokeMethodExpression.Update(
+                            arguments:
+                            [
+                                invokeMethodExpression.Arguments[0]
+                                    .Invoke("GetProperty", Literal(resultSegment)),
+                                ..invokeMethodExpression.Arguments.Skip(1)
+                            ]);
+                    }
                 }
             }
         }

eng/packages/http-client-csharp/generator/Azure.Generator/test/Visitors/LroVisitorTests.cs

@@ -162,6 +162,15 @@ public void UpdatesExplicitOperatorToUseResultSegment()
             Assert.IsNotNull(explicitOperator!.BodyStatements);
             var result = explicitOperator!.BodyStatements!.ToDisplayString();
             Assert.AreEqual(Helpers.GetExpectedFromFile(), result);
+
+            // does not mutate an already mutated operator
+            visitor.InvokeVisitServiceMethod(lroServiceMethod, clientProvider!, methodCollection);
+            serializationProvider = responseModelProvider!.SerializationProviders[0];
+            explicitOperator = serializationProvider.Methods
+                .FirstOrDefault(m => m.Signature.Modifiers.HasFlag(MethodSignatureModifiers.Explicit) &&
+                                     m.Signature.Modifiers.HasFlag(MethodSignatureModifiers.Operator));
+            result = explicitOperator!.BodyStatements!.ToDisplayString();
+            Assert.AreEqual(Helpers.GetExpectedFromFile(), result);
         }
 
         [Test]