Delegate UnboundLambda to BoundLambda conversion to the semantic model.

src/Compilers/CSharp/Portable/Compilation/MemberSemanticModel.cs

@@ -51,7 +51,7 @@ protected MemberSemanticModel(CSharpCompilation compilation, CSharpSyntaxNode ro
             _parentSemanticModelOpt = parentSemanticModelOpt;
             _speculatedPosition = speculatedPosition;
 
-            _operationFactory = new CSharpOperationFactory();
+            _operationFactory = new CSharpOperationFactory(this);
         }
 
         public override CSharpCompilation Compilation
@@ -983,6 +983,10 @@ internal override IOperation GetOperationWorker(CSharpSyntaxNode node, GetOperat
                     break;
             }
 
+            // The CSharp operation factory assumes that UnboundLambda will be bound for error recovery and never be passed to the factory
+            // as the start of a tree to get operations for. This is guaranteed by the builder that populates the node map, as it will call
+            // UnboundLambda.BindForErrorRecovery() when it encounters an UnboundLambda node.
+            Debug.Assert(result.Kind != BoundKind.UnboundLambda);
             return _operationFactory.Create(result);
         }
 

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

@@ -3,6 +3,7 @@
 using System;
 using System.Collections.Concurrent;
 using System.Collections.Immutable;
+using System.Diagnostics;
 using System.Linq;
 using Microsoft.CodeAnalysis.CSharp;
 using Microsoft.CodeAnalysis.CSharp.Symbols;
@@ -13,6 +14,12 @@ internal sealed partial class CSharpOperationFactory
     {
         private readonly ConcurrentDictionary<BoundNode, IOperation> _cache =
             new ConcurrentDictionary<BoundNode, IOperation>(concurrencyLevel: 2, capacity: 10);
+        private readonly SemanticModel _semanticModel;
+
+        public CSharpOperationFactory(SemanticModel semanticModel)
+        {
+            _semanticModel = semanticModel;
+        }
 
         public IOperation Create(BoundNode boundNode)
         {
@@ -353,18 +360,15 @@ private IObjectCreationExpression CreateBoundObjectCreationExpressionOperation(B
             return new LazyObjectCreationExpression(constructor, memberInitializers, argumentsInEvaluationOrder, isInvalid, syntax, type, constantValue);
         }
 
-        private ILambdaExpression CreateUnboundLambdaOperation(UnboundLambda unboundLambda)
+        private IOperation CreateUnboundLambdaOperation(UnboundLambda unboundLambda)
         {
-            bool isInvalid = unboundLambda.HasErrors;
-            SyntaxNode syntax = unboundLambda.Syntax;
-            // This matches the SemanticModel implementation. This is because in VB, lambdas by themselves
-            // do not have a type. To get the type of a lambda expression in the SemanticModel, you need to look at
-            // TypeInfo.ConvertedType, rather than TypeInfo.Type. We replicate that behavior here. To get the type of
-            // an IUnboundLambdaExpression, you need to look at the parent IConversionExpression.
-            ITypeSymbol type = null;
-            Optional<object> constantValue = ConvertToOptional(unboundLambda.ConstantValue);
-            Lazy<ILambdaExpression> internalLambda = new Lazy<ILambdaExpression>(() => CreateBoundLambdaOperation(unboundLambda.BindForErrorRecovery()));
-            return new LazyLambdaFromUnboundLambdaExpression(internalLambda, isInvalid, syntax, type, constantValue);
+            // We want to ensure that we never see the UnboundLambda node, and that we don't end up having two different IOperation
+            // nodes for the lambda expression. So, we ask the semantic model for the IOperation node for the unbound lambda syntax.
+            // We are counting on the fact that will do the error recovery and actually create the BoundLambda node appropriate for
+            // this syntax node.
+            var lambdaOperation = _semanticModel.GetOperationInternal(unboundLambda.Syntax);
+            Debug.Assert(lambdaOperation.Kind == OperationKind.LambdaExpression);
+            return lambdaOperation;
         }
 
         private ILambdaExpression CreateBoundLambdaOperation(BoundLambda boundLambda)

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

-using Microsoft.CodeAnalysis.CSharp.Syntax;
+using System.Linq;
+using Microsoft.CodeAnalysis.CSharp.Syntax;
+using Microsoft.CodeAnalysis.Semantics;
 using Microsoft.CodeAnalysis.Test.Utilities;
 using Xunit;
 
@@ -112,5 +114,49 @@ static void F()
 
             VerifyOperationTreeAndDiagnosticsForTest<EqualsValueClauseSyntax>(source, expectedOperationTree, expectedDiagnostics);
         }
+
+        [Fact]
+        public void ILambdaExpression_UnboundLambda_ReferenceEquality()
+        {
+           string source = @"
+using System;
+
+class Program
+{
+    static void Main(string[] args)
+    {
+        var x /*<bind>*/= () => F()/*</bind>*/;
+    }
+
+    static void F()
+    {
+    }
+}
+";
+
+            var compilation = CreateCompilationWithMscorlibAndSystemCore(source);
+            var syntaxTree = compilation.SyntaxTrees[0];
+            var semanticModel = compilation.GetSemanticModel(syntaxTree);
+
+            var variableDeclaration = syntaxTree.GetRoot().DescendantNodes().OfType<VariableDeclarationSyntax>().Single();
+            var lambdaSyntax = (LambdaExpressionSyntax)variableDeclaration.Variables.Single().Initializer.Value;
+
+            var variableDeclarationOperation = (IVariableDeclarationStatement)semanticModel.GetOperationInternal(variableDeclaration);
+            var variableTreeLambdaOperation = (ILambdaExpression)variableDeclarationOperation.Declarations.Single().Initializer;
+            var lambdaOperation = (ILambdaExpression)semanticModel.GetOperationInternal(lambdaSyntax);
+
+            // Assert that both ways of getting to the lambda (requesting the lambda directly, and requesting via the lambda syntax)
+            // return the same bound node.
+            Assert.Same(variableTreeLambdaOperation, lambdaOperation);
+
+            var variableDeclarationOperationSecondRequest = (IVariableDeclarationStatement)semanticModel.GetOperationInternal(variableDeclaration);
+            var variableTreeLambdaOperationSecondRequest = (ILambdaExpression)variableDeclarationOperation.Declarations.Single().Initializer;
+            var lambdaOperationSecondRequest = (ILambdaExpression)semanticModel.GetOperationInternal(lambdaSyntax);
+
+            // Assert that, when request the variable declaration or the lambda for a second time, there is no rebinding of the
+            // underlying UnboundLambda, and we get the same ILambdaExpression as before
+            Assert.Same(variableTreeLambdaOperation, variableTreeLambdaOperationSecondRequest);
+            Assert.Same(lambdaOperation, lambdaOperationSecondRequest);
+        }
     }
 }