PR feedbacks.

reverted encoding only changes
marked as implicit for expression statement that doesn't point to expression syntax node
added tracking bug in the comment

src/Compilers/CSharp/Portable/Operations/CSharpOperationFactory.cs

@@ -1381,7 +1381,11 @@ private IExpressionStatement CreateBoundExpressionStatementOperation(BoundExpres
             SyntaxNode syntax = boundExpressionStatement.Syntax;
             ITypeSymbol type = null;
             Optional<object> constantValue = default(Optional<object>);
-            bool isImplicit = boundExpressionStatement.WasCompilerGenerated;
+
+            // lambda body can point to expression directly and binder can insert exression statement there. and end up statement pointing to
+            // expression syntax node since there is no statement syntax node to point to. this will mark such one as implicit since it doesn't
+            // actually exist in code
+            bool isImplicit = boundExpressionStatement.WasCompilerGenerated || !boundExpressionStatement.Syntax.IsKind(SyntaxKind.ExpressionStatement);
             return new LazyExpressionStatement(expression, _semanticModel, syntax, type, constantValue, isImplicit);
         }
 

src/Compilers/CSharp/Test/Semantic/IOperation/IOperationTests_IAnonymousFunctionExpression.cs

@@ -60,7 +60,7 @@ class Program
 {
     static void Main(string[] args)
     {
-        Action x = /*<bind>*/() => F();/*</bind>*/
+        Action x = /*<bind>*/() => F()/*</bind>*/;
     }
 
     static void F()
@@ -70,13 +70,13 @@ static void F()
 ";
             string expectedOperationTree = @"
 IAnonymousFunctionExpression (Symbol: lambda expression) (OperationKind.AnonymousFunctionExpression, Type: null) (Syntax: '() => F()')
-    IBlockStatement (2 statements) (OperationKind.BlockStatement) (Syntax: 'F()')
-        IExpressionStatement (OperationKind.ExpressionStatement) (Syntax: 'F()')
-        Expression: IInvocationExpression (void Program.F()) (OperationKind.InvocationExpression, Type: System.Void) (Syntax: 'F()')
-            Instance Receiver: null
-            Arguments(0)
-        IReturnStatement (OperationKind.ReturnStatement) (Syntax: 'F()')
-        ReturnedValue: null
+  IBlockStatement (2 statements) (OperationKind.BlockStatement) (Syntax: 'F()')
+    IExpressionStatement (OperationKind.ExpressionStatement) (Syntax: 'F()')
+      Expression: IInvocationExpression (void Program.F()) (OperationKind.InvocationExpression, Type: System.Void) (Syntax: 'F()')
+          Instance Receiver: null
+          Arguments(0)
+    IReturnStatement (OperationKind.ReturnStatement) (Syntax: 'F()')
+      ReturnedValue: null
 ";
             var expectedDiagnostics = DiagnosticDescription.None;
 

src/Compilers/CSharp/Test/Semantic/IOperation/IOperationTests_IDynamicMemberReferenceExpression.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.
+// 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 Microsoft.CodeAnalysis.CSharp.Syntax;
 using Microsoft.CodeAnalysis.Test.Utilities;

src/Compilers/CSharp/Test/Semantic/IOperation/IOperationTests_IFieldReferenceExpression.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.
+// 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 Microsoft.CodeAnalysis.CSharp.Syntax;
 using Microsoft.CodeAnalysis.CSharp.Test.Utilities;

src/Compilers/CSharp/Test/Semantic/IOperation/IOperationTests_ILocalReferenceExpression.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.
+// 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 Microsoft.CodeAnalysis.CSharp.Syntax;

src/Compilers/CSharp/Test/Semantic/Semantics/ObjectAndCollectionInitializerTests.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.
+// 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.Linq;
 using Microsoft.CodeAnalysis.CSharp.Syntax;
@@ -2935,14 +2935,13 @@ static void Main()
 }
 ";
             string expectedOperationTree = @"
-IExpressionStatement (OperationKind.ExpressionStatement, IsInvalid) (Syntax: 'new C { 1 }')
-  Expression: IObjectCreationExpression (Constructor: C..ctor()) (OperationKind.ObjectCreationExpression, Type: C, IsInvalid) (Syntax: 'new C { 1 }')
-      Arguments(0)
-      Initializer: IObjectOrCollectionInitializerExpression (OperationKind.ObjectOrCollectionInitializerExpression, Type: C, IsInvalid) (Syntax: '{ 1 }')
-          Initializers(1):
-              ICollectionElementInitializerExpression (AddMethod: void C.Add(System.Int32 i)) (IsDynamic: False) (OperationKind.CollectionElementInitializerExpression, Type: System.Void, IsInvalid) (Syntax: '1')
-                Arguments(1):
-                    ILiteralExpression (OperationKind.LiteralExpression, Type: System.Int32, Constant: 1, IsInvalid) (Syntax: '1')
+IObjectCreationExpression (Constructor: C..ctor()) (OperationKind.ObjectCreationExpression, Type: C, IsInvalid) (Syntax: 'new C { 1 }')
+  Arguments(0)
+  Initializer: IObjectOrCollectionInitializerExpression (OperationKind.ObjectOrCollectionInitializerExpression, Type: C, IsInvalid) (Syntax: '{ 1 }')
+      Initializers(1):
+          ICollectionElementInitializerExpression (AddMethod: void C.Add(System.Int32 i)) (IsDynamic: False) (OperationKind.CollectionElementInitializerExpression, Type: System.Void, IsInvalid) (Syntax: '1')
+            Arguments(1):
+                ILiteralExpression (OperationKind.LiteralExpression, Type: System.Int32, Constant: 1, IsInvalid) (Syntax: '1')
 ";
             var expectedDiagnostics = new DiagnosticDescription[] {
                 // CS0765: Partial methods with only a defining declaration or removed conditional methods cannot be used in expression trees

src/Compilers/CSharp/Test/Semantic/Semantics/OutVarTests.cs

@@ -1070,6 +1070,11 @@ private static void VerifyModelForOutVarInNotExecutableCode(SemanticModel model,
 
         private static void AssertTypeFromOperation(SemanticModel model, TypeSymbol expectedType, DeclarationExpressionSyntax decl)
         {
+            // see https://github.com/dotnet/roslyn/issues/22175 for more detail.
+
+            // unlike GetSymbolInfo or GetTypeInfo, GetOperation doesn't use SemanticModel's recovery mode.
+            // what that means is that GetOperation might return null for ones GetSymbol/GetTypeInfo do return info from
+            // error recovery mode
             var variableDeclarator = decl.Ancestors().OfType<VariableDeclaratorSyntax>().FirstOrDefault();
             if (variableDeclarator?.ArgumentList?.FullSpan.Contains(decl.Span) == true)
             {

src/Compilers/VisualBasic/Portable/Binding/MemberSemanticModel.vb

@@ -795,6 +795,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic
 
         Friend Overrides Function GetOperationWorker(node As VisualBasicSyntaxNode, cancellationToken As CancellationToken) As IOperation
             ' see whether we can bind smaller scope than GetBindingRoot to make perf better
+            ' https://github.com/dotnet/roslyn/issues/22176
             Dim bindingRoot = DirectCast(GetBindingRoot(node), VisualBasicSyntaxNode)
 
             Dim statementOrRootOperation As IOperation = GetStatementOrRootOperation(bindingRoot, cancellationToken)