changed to return IEnumerable<IOpeartion> from ImmutableArray<IOperation> for...

changed to return IEnumerable<IOpeartion> from ImmutableArray<IOperation> for IOperationHasChildren and made all IOperation to implement that interface

src/Compilers/Core/Portable/Operations/IInvalidExpression.cs

 // Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
 
-using System.Collections.Immutable;
+using System.Collections.Generic;
 
 namespace Microsoft.CodeAnalysis.Semantics
 {
@@ -13,7 +13,7 @@ public interface IInvalidExpression : IOperation
         /// <summary>
         /// Child operations.
         /// </summary>
-        ImmutableArray<IOperation> Children { get; }
+        IEnumerable<IOperation> Children { get; }
     }
 }
 

src/Compilers/Core/Portable/Operations/IInvalidStatement.cs

 // Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
 
-using System.Collections.Immutable;
+using System.Collections.Generic;
 
 namespace Microsoft.CodeAnalysis.Semantics
 {
@@ -16,7 +16,7 @@ public interface IInvalidStatement : IOperation
         /// <summary>
         /// Child operations.
         /// </summary>
-        ImmutableArray<IOperation> Children { get; }
+        IEnumerable<IOperation> Children { get; }
     }
 }
 

src/Compilers/Core/Portable/Operations/IOperationWithChildren.cs

 // Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
 
+using System.Collections.Generic;
 using System.Collections.Immutable;
 using System.Runtime.CompilerServices;
 
@@ -18,6 +19,6 @@ internal interface IOperationWithChildren: IOperation
         /// An array of child operations for this operation.
         /// </summary>
         /// <remarks>Note that any of the child operation nodes may be null.</remarks>
-        ImmutableArray<IOperation> Children { get; }
+        IEnumerable<IOperation> Children { get; }
     }
 }

src/Compilers/Core/Portable/Operations/Operation.cs

 // Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
 
 using System;
+using System.Collections.Generic;
 using System.Collections.Immutable;
 using Microsoft.CodeAnalysis.Semantics;
 
@@ -9,7 +10,7 @@ namespace Microsoft.CodeAnalysis
     /// <summary>
     /// Root type for representing the abstract semantics of C# and VB statements and expressions.
     /// </summary>
-    internal abstract class Operation : IOperation
+    internal abstract class Operation : IOperation, IOperationWithChildren
     {
         public Operation(OperationKind kind, SyntaxNode syntax, ITypeSymbol type, Optional<object> constantValue)
         {
@@ -39,6 +40,8 @@ public Operation(OperationKind kind, SyntaxNode syntax, ITypeSymbol type, Option
         /// </summary>
         public Optional<object> ConstantValue { get; }
 
+        public abstract IEnumerable<IOperation> Children { get; }
+
         public abstract void Accept(OperationVisitor visitor);
 
         public abstract TResult Accept<TArgument, TResult>(OperationVisitor<TArgument, TResult> visitor, TArgument argument);
@@ -77,7 +80,7 @@ public void Accept(OperationVisitor visitor)
                 return visitor.VisitNoneOperation(this, argument);
             }
 
-            public ImmutableArray<IOperation> Children => _getChildren();
+            public IEnumerable<IOperation> Children => _getChildren().NullToEmpty();
         }
     }
 }

src/Compilers/Core/Portable/Operations/OperationWalker.cs

 // Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
 
-using System.Collections.Immutable;
+using System.Collections.Generic;
 
 namespace Microsoft.CodeAnalysis.Semantics
 {
@@ -12,14 +12,11 @@ public abstract class OperationWalker : OperationVisitor
     {
         private int _recursionDepth;
 
-        internal void VisitArray<T>(ImmutableArray<T> list) where T : IOperation
+        internal void VisitArray<T>(IEnumerable<T> list) where T : IOperation
         {
-            if (!list.IsDefault)
+            foreach (var operation in list)
             {
-                foreach (var operation in list)
-                {
-                    Visit(operation);
-                }
+                Visit(operation);
             }
         }
 
@@ -40,7 +37,7 @@ public override void Visit(IOperation operation)
             }
         }
 
-        internal override void VisitNoneOperation(IOperation operation)
+        public override void DefaultVisit(IOperation operation)
         {
             if (operation is IOperationWithChildren operationWithChildren)
             {
@@ -48,430 +45,12 @@ internal override void VisitNoneOperation(IOperation operation)
             }
         }
 
-        public override void VisitBlockStatement(IBlockStatement operation)
-        {
-            VisitArray(operation.Statements);
-        }
-
-        public override void VisitVariableDeclarationStatement(IVariableDeclarationStatement operation)
-        {
-            VisitArray(operation.Declarations);
-        }
-
-        public override void VisitVariableDeclaration(IVariableDeclaration operation)
-        {
-            Visit(operation.Initializer);
-        }
-
-        public override void VisitSwitchStatement(ISwitchStatement operation)
-        {
-            Visit(operation.Value);
-            VisitArray(operation.Cases);
-        }
-
-        public override void VisitSwitchCase(ISwitchCase operation)
-        {
-            VisitArray(operation.Clauses);
-            VisitArray(operation.Body);
-        }
-
-        public override void VisitSingleValueCaseClause(ISingleValueCaseClause operation)
-        {
-            Visit(operation.Value);
-        }
-
-        public override void VisitRelationalCaseClause(IRelationalCaseClause operation)
-        {
-            Visit(operation.Value);
-        }
-
-        public override void VisitRangeCaseClause(IRangeCaseClause operation)
-        {
-            Visit(operation.MinimumValue);
-            Visit(operation.MaximumValue);
-        }
-
-        public override void VisitDefaultCaseClause(IDefaultCaseClause operation)
-        {
-        }
-
-        public override void VisitIfStatement(IIfStatement operation)
-        {
-            Visit(operation.Condition);
-            Visit(operation.IfTrueStatement);
-            Visit(operation.IfFalseStatement);
-        }
-
-        public override void VisitWhileUntilLoopStatement(IWhileUntilLoopStatement operation)
+        internal override void VisitNoneOperation(IOperation operation)
         {
-            if (operation.IsTopTest)
-            {
-                Visit(operation.Condition);
-                Visit(operation.Body);
-            }
-            else
+            if (operation is IOperationWithChildren operationWithChildren)
             {
-                Visit(operation.Body);
-                Visit(operation.Condition);
+                VisitArray(operationWithChildren.Children);
             }
         }
-
-        public override void VisitForLoopStatement(IForLoopStatement operation)
-        {
-            VisitArray(operation.Before);
-            Visit(operation.Condition);
-            Visit(operation.Body);
-            VisitArray(operation.AtLoopBottom);
-        }
-
-        public override void VisitForEachLoopStatement(IForEachLoopStatement operation)
-        {
-            Visit(operation.Collection);
-            Visit(operation.Body);
-        }
-
-        public override void VisitLabelStatement(ILabelStatement operation)
-        {
-            Visit(operation.LabeledStatement);
-        }
-
-        public override void VisitBranchStatement(IBranchStatement operation)
-        { }
-
-        public override void VisitYieldBreakStatement(IReturnStatement operation)
-        { }
-
-        public override void VisitEmptyStatement(IEmptyStatement operation)
-        { }
-
-        public override void VisitThrowStatement(IThrowStatement operation)
-        {
-            Visit(operation.ThrownObject);
-        }
-
-        public override void VisitReturnStatement(IReturnStatement operation)
-        {
-            Visit(operation.ReturnedValue);
-        }
-
-        public override void VisitLockStatement(ILockStatement operation)
-        {
-            Visit(operation.LockedObject);
-            Visit(operation.Body);
-        }
-
-        public override void VisitTryStatement(ITryStatement operation)
-        {
-            Visit(operation.Body);
-            VisitArray(operation.Catches);
-            Visit(operation.FinallyHandler);
-        }
-
-        public override void VisitCatchClause(ICatchClause operation)
-        {
-            Visit(operation.Filter);
-            Visit(operation.Handler);
-        }
-
-        public override void VisitUsingStatement(IUsingStatement operation)
-        {
-            Visit(operation.Declaration);
-            Visit(operation.Value);
-            Visit(operation.Body);
-        }
-
-        public override void VisitFixedStatement(IFixedStatement operation)
-        {
-            Visit(operation.Variables);
-            Visit(operation.Body);
-        }
-
-        public override void VisitExpressionStatement(IExpressionStatement operation)
-        {
-            Visit(operation.Expression);
-        }
-
-        public override void VisitWithStatement(IWithStatement operation)
-        {
-            Visit(operation.Value);
-            Visit(operation.Body);
-        }
-
-        public override void VisitStopStatement(IStopStatement operation)
-        { }
-
-        public override void VisitEndStatement(IEndStatement operation)
-        { }
-
-        public override void VisitInvocationExpression(IInvocationExpression operation)
-        {
-            Visit(operation.Instance);
-            VisitArray(operation.ArgumentsInEvaluationOrder);
-        }
-
-        public override void VisitArgument(IArgument operation)
-        {
-            Visit(operation.Value);
-            Visit(operation.InConversion);
-            Visit(operation.OutConversion);
-        }
-
-        public override void VisitOmittedArgumentExpression(IOmittedArgumentExpression operation)
-        { }
-
-        public override void VisitArrayElementReferenceExpression(IArrayElementReferenceExpression operation)
-        {
-            Visit(operation.ArrayReference);
-            VisitArray(operation.Indices);
-        }
-
-        public override void VisitPointerIndirectionReferenceExpression(IPointerIndirectionReferenceExpression operation)
-        {
-            Visit(operation.Pointer);
-        }
-
-        public override void VisitLocalReferenceExpression(ILocalReferenceExpression operation)
-        { }
-
-        public override void VisitParameterReferenceExpression(IParameterReferenceExpression operation)
-        { }
-
-        public override void VisitSyntheticLocalReferenceExpression(ISyntheticLocalReferenceExpression operation)
-        { }
-
-        public override void VisitInstanceReferenceExpression(IInstanceReferenceExpression operation)
-        { }
-
-        public override void VisitFieldReferenceExpression(IFieldReferenceExpression operation)
-        {
-            Visit(operation.Instance);
-        }
-
-        public override void VisitMethodBindingExpression(IMethodBindingExpression operation)
-        {
-            Visit(operation.Instance);
-        }
-
-        public override void VisitPropertyReferenceExpression(IPropertyReferenceExpression operation)
-        {
-            Visit(operation.Instance);
-            VisitArray(operation.ArgumentsInEvaluationOrder);
-        }
-
-        public override void VisitEventReferenceExpression(IEventReferenceExpression operation)
-        {
-            Visit(operation.Instance);
-        }
-
-        public override void VisitEventAssignmentExpression(IEventAssignmentExpression operation)
-        {
-            Visit(operation.EventInstance);
-            Visit(operation.HandlerValue);
-        }
-
-        public override void VisitConditionalAccessExpression(IConditionalAccessExpression operation)
-        {
-            Visit(operation.ConditionalInstance);
-            Visit(operation.ConditionalValue);
-        }
-
-        public override void VisitConditionalAccessInstanceExpression(IConditionalAccessInstanceExpression operation)
-        {
-        }
-
-        public override void VisitPlaceholderExpression(IPlaceholderExpression operation)
-        {
-        }
-
-        public override void VisitUnaryOperatorExpression(IUnaryOperatorExpression operation)
-        {
-            Visit(operation.Operand);
-        }
-
-        public override void VisitBinaryOperatorExpression(IBinaryOperatorExpression operation)
-        {
-            Visit(operation.LeftOperand);
-            Visit(operation.RightOperand);
-        }
-
-        public override void VisitConversionExpression(IConversionExpression operation)
-        {
-            Visit(operation.Operand);
-        }
-
-        public override void VisitConditionalChoiceExpression(IConditionalChoiceExpression operation)
-        {
-            Visit(operation.Condition);
-            Visit(operation.IfTrueValue);
-            Visit(operation.IfFalseValue);
-        }
-
-        public override void VisitNullCoalescingExpression(INullCoalescingExpression operation)
-        {
-            Visit(operation.PrimaryOperand);
-            Visit(operation.SecondaryOperand);
-        }
-
-        public override void VisitIsTypeExpression(IIsTypeExpression operation)
-        {
-            Visit(operation.Operand);
-        }
-
-        public override void VisitSizeOfExpression(ISizeOfExpression operation)
-        { }
-
-        public override void VisitTypeOfExpression(ITypeOfExpression operation)
-        { }
-
-        public override void VisitLambdaExpression(ILambdaExpression operation)
-        {
-            Visit(operation.Body);
-        }
-
-        public override void VisitLocalFunctionStatement(ILocalFunctionStatement operation)
-        {
-            Visit(operation.Body);
-        }
-
-        public override void VisitLiteralExpression(ILiteralExpression operation)
-        { }
-
-        public override void VisitAwaitExpression(IAwaitExpression operation)
-        {
-            Visit(operation.AwaitedValue);
-        }
-
-        public override void VisitNameOfExpression(INameOfExpression operation)
-        {
-            Visit(operation.Argument);
-        }
-
-        public override void VisitThrowExpression(IThrowExpression operation)
-        {
-            Visit(operation.Expression);
-        }
-
-        public override void VisitAddressOfExpression(IAddressOfExpression operation)
-        {
-            Visit(operation.Reference);
-        }
-
-        public override void VisitObjectCreationExpression(IObjectCreationExpression operation)
-        {
-            VisitArray(operation.ArgumentsInEvaluationOrder);
-            VisitArray(operation.Initializers);
-        }
-
-        public override void VisitAnonymousObjectCreationExpression(IAnonymousObjectCreationExpression operation)
-        {
-            VisitArray(operation.Initializers);
-        }
-
-        public override void VisitFieldInitializer(IFieldInitializer operation)
-        {
-            Visit(operation.Value);
-        }
-
-        public override void VisitPropertyInitializer(IPropertyInitializer operation)
-        {
-            Visit(operation.Value);
-        }
-
-        public override void VisitParameterInitializer(IParameterInitializer operation)
-        {
-            Visit(operation.Value);
-        }
-
-        public override void VisitArrayCreationExpression(IArrayCreationExpression operation)
-        {
-            VisitArray(operation.DimensionSizes);
-            Visit(operation.Initializer);
-        }
-
-        public override void VisitArrayInitializer(IArrayInitializer operation)
-        {
-            VisitArray(operation.ElementValues);
-        }
-
-        public override void VisitSimpleAssignmentExpression(ISimpleAssignmentExpression operation)
-        {
-            Visit(operation.Target);
-            Visit(operation.Value);
-        }
-
-        public override void VisitCompoundAssignmentExpression(ICompoundAssignmentExpression operation)
-        {
-            Visit(operation.Target);
-            Visit(operation.Value);
-        }
-
-        public override void VisitIncrementExpression(IIncrementExpression operation)
-        {
-            Visit(operation.Target);
-        }
-
-        public override void VisitParenthesizedExpression(IParenthesizedExpression operation)
-        {
-            Visit(operation.Operand);
-        }
-
-        public override void VisitLateBoundMemberReferenceExpression(ILateBoundMemberReferenceExpression operation)
-        {
-            Visit(operation.Instance);
-        }
-
-        public override void VisitDefaultValueExpression(IDefaultValueExpression operation)
-        { }
-
-        public override void VisitTypeParameterObjectCreationExpression(ITypeParameterObjectCreationExpression operation)
-        { }
-
-        public override void VisitInvalidStatement(IInvalidStatement operation)
-        {
-            VisitArray(operation.Children);
-        }
-
-        public override void VisitInvalidExpression(IInvalidExpression operation)
-        {
-            VisitArray(operation.Children);
-        }
-
-        public override void VisitInterpolatedStringExpression(IInterpolatedStringExpression operation)
-        {
-            VisitArray(operation.Parts);
-        }
-
-        public override void VisitInterpolatedStringText(IInterpolatedStringText operation)
-        {
-            Visit(operation.Text);
-        }
-
-        public override void VisitInterpolation(IInterpolation operation)
-        {
-            Visit(operation.Expression);
-            Visit(operation.Alignment);
-            Visit(operation.FormatString);
-        }
-
-        public override void VisitConstantPattern(IConstantPattern operation)
-        {
-            Visit(operation.Value);
-        }
-
-        public override void VisitDeclarationPattern(IDeclarationPattern operation)
-        {
-        }
-
-        public override void VisitIsPatternExpression(IIsPatternExpression operation)
-        {
-            Visit(operation.Expression);
-            Visit(operation.Pattern);
-        }
-
-        public override void VisitPatternCaseClause(IPatternCaseClause operation)
-        {
-            Visit(operation.Pattern);
-            Visit(operation.GuardExpression);
-        }
     }
 }

src/Test/Utilities/Portable/Compilation/OperationTreeVerifier.cs

@@ -232,17 +232,12 @@ private void Visit(IOperation operation, string header)
             Unindent();
         }
 
-        private void VisitArray<T>(ImmutableArray<T> list, string header, bool logElementCount)
+        private void VisitArray<T>(IEnumerable<T> list, string header, bool logElementCount)
             where T : IOperation
         {
             Debug.Assert(!string.IsNullOrEmpty(header));
 
-            if (list.IsDefaultOrEmpty)
-            {
-                return;
-            }
-
-            var elementCount = logElementCount ? $"({list.Length})" : string.Empty;
+            var elementCount = logElementCount ? $"({list.Count()})" : string.Empty;
             Indent();
             LogString($"{header}{elementCount}: ");
             VisitArray(list);