Add nullable annotations to NullableWalker

src/Compilers/CSharp/Portable/BoundTree/BoundExpressionWithNullability.cs

@@ -10,7 +10,7 @@ namespace Microsoft.CodeAnalysis.CSharp
 {
     internal sealed partial class BoundExpressionWithNullability : BoundExpression
     {
-        public BoundExpressionWithNullability(SyntaxNode syntax, BoundExpression expression, NullableAnnotation nullableAnnotation, TypeSymbol type)
+        public BoundExpressionWithNullability(SyntaxNode syntax, BoundExpression expression, NullableAnnotation nullableAnnotation, TypeSymbol? type)
             : this(syntax, expression, nullableAnnotation, type, hasErrors: false)
         {
             IsSuppressed = expression.IsSuppressed;

src/Compilers/CSharp/Portable/BoundTree/BoundNodes.xml

@@ -511,6 +511,8 @@
   </Node>
 
   <Node Name="BoundNullCoalescingOperator" Base="BoundExpression">
+    <!-- Non-null type is required for this node kind -->
+    <Field Name="Type" Type="TypeSymbol" Override="true" Null="disallow"/>
     <Field Name="LeftOperand" Type="BoundExpression"/>
     <Field Name="RightOperand" Type="BoundExpression"/>
     <Field Name="LeftConversion" Type="Conversion"/>

src/Compilers/CSharp/Portable/BoundTree/NullabilityRewriter.cs

@@ -50,15 +50,15 @@ private BoundNode VisitBinaryOperatorBase(BoundBinaryOperatorBase binaryOperator
             {
                 currentBinary = stack.Pop();
 
-                bool foundInfo = _updatedNullabilities.TryGetValue(currentBinary, out (NullabilityInfo Info, TypeSymbol Type) infoAndType);
+                bool foundInfo = _updatedNullabilities.TryGetValue(currentBinary, out (NullabilityInfo Info, TypeSymbol? Type) infoAndType);
                 var right = (BoundExpression)Visit(currentBinary.Right);
                 var type = foundInfo ? infoAndType.Type : currentBinary.Type;
 
                 currentBinary = currentBinary switch
                 {
-                    BoundBinaryOperator binary => binary.Update(binary.OperatorKind, binary.ConstantValueOpt, GetUpdatedSymbol(binary, binary.MethodOpt), binary.ResultKind, binary.OriginalUserDefinedOperatorsOpt, leftChild, right, type),
+                    BoundBinaryOperator binary => binary.Update(binary.OperatorKind, binary.ConstantValueOpt, GetUpdatedSymbol(binary, binary.MethodOpt), binary.ResultKind, binary.OriginalUserDefinedOperatorsOpt, leftChild, right, type!),
                     // https://github.com/dotnet/roslyn/issues/35031: We'll need to update logical.LogicalOperator
-                    BoundUserDefinedConditionalLogicalOperator logical => logical.Update(logical.OperatorKind, logical.LogicalOperator, logical.TrueOperator, logical.FalseOperator, logical.ResultKind, logical.OriginalUserDefinedOperatorsOpt, leftChild, right, type),
+                    BoundUserDefinedConditionalLogicalOperator logical => logical.Update(logical.OperatorKind, logical.LogicalOperator, logical.TrueOperator, logical.FalseOperator, logical.ResultKind, logical.OriginalUserDefinedOperatorsOpt, leftChild, right, type!),
                     _ => throw ExceptionUtilities.UnexpectedValue(currentBinary.Kind),
                 };
 

src/Compilers/CSharp/Portable/FlowAnalysis/LocalDataFlowPass.cs

@@ -2,8 +2,11 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
+#nullable enable
+
 using System;
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 using System.Linq;
 using Microsoft.CodeAnalysis.CSharp.Symbols;
 using Microsoft.CodeAnalysis.PooledObjects;
@@ -58,7 +61,7 @@ internal interface ILocalDataFlowState : ILocalState
 
         protected LocalDataFlowPass(
             CSharpCompilation compilation,
-            Symbol member,
+            Symbol? member,
             BoundNode node,
             EmptyStructTypeCache emptyStructs,
             bool trackUnassignments,
@@ -113,7 +116,6 @@ protected virtual bool IsEmptyStructType(TypeSymbol type)
             return _emptyStructTypeCache.IsEmptyStructType(type);
         }
 
-#nullable enable
         /// <summary>
         /// Force a variable to have a slot.  Returns -1 if the variable has an empty struct type.
         /// </summary>
@@ -171,7 +173,6 @@ protected virtual int GetOrCreateSlot(Symbol symbol, int containingSlot = 0, boo
 
             return slot;
         }
-#nullable restore
 
         private int GetSlotDepth(int slot)
         {
@@ -199,8 +200,7 @@ private int GetSlotDepth(int slot)
         /// </summary>
         private int DescendThroughTupleRestFields(ref Symbol symbol, int containingSlot, bool forceContainingSlotsToExist)
         {
-            var fieldSymbol = symbol as TupleFieldSymbol;
-            if ((object)fieldSymbol != null)
+            if (symbol is TupleFieldSymbol fieldSymbol)
             {
                 TypeSymbol containingType = symbol.ContainingType;
 
@@ -236,7 +236,7 @@ private int DescendThroughTupleRestFields(ref Symbol symbol, int containingSlot,
             return containingSlot;
         }
 
-        protected abstract bool TryGetReceiverAndMember(BoundExpression expr, out BoundExpression receiver, out Symbol member);
+        protected abstract bool TryGetReceiverAndMember(BoundExpression expr, out BoundExpression? receiver, [NotNullWhen(true)] out Symbol? member);
 
         protected Symbol GetNonMemberSymbol(int slot)
         {
@@ -271,7 +271,7 @@ protected virtual int MakeSlot(BoundExpression node)
                 case BoundKind.FieldAccess:
                 case BoundKind.EventAccess:
                 case BoundKind.PropertyAccess:
-                    if (TryGetReceiverAndMember(node, out BoundExpression receiver, out Symbol member))
+                    if (TryGetReceiverAndMember(node, out BoundExpression? receiver, out Symbol? member))
                     {
                         Debug.Assert((receiver is null) != member.RequiresInstanceReceiver());
                         return MakeMemberSlot(receiver, member);
@@ -283,7 +283,7 @@ protected virtual int MakeSlot(BoundExpression node)
             return -1;
         }
 
-        protected int MakeMemberSlot(BoundExpression receiverOpt, Symbol member)
+        protected int MakeMemberSlot(BoundExpression? receiverOpt, Symbol member)
         {
             int containingSlot;
             if (member.RequiresInstanceReceiver())

src/Compilers/CSharp/Portable/FlowAnalysis/NullableWalker.DebugVerifier.cs

@@ -18,12 +18,12 @@ internal sealed partial class NullableWalker
         /// </summary>
         private sealed class DebugVerifier : BoundTreeWalker
         {
-            private readonly ImmutableDictionary<BoundExpression, (NullabilityInfo Info, TypeSymbol Type)> _analyzedNullabilityMap;
+            private readonly ImmutableDictionary<BoundExpression, (NullabilityInfo Info, TypeSymbol? Type)> _analyzedNullabilityMap;
             private readonly SnapshotManager? _snapshotManager;
             private readonly HashSet<BoundExpression> _visitedExpressions = new HashSet<BoundExpression>();
             private int _recursionDepth;
 
-            private DebugVerifier(ImmutableDictionary<BoundExpression, (NullabilityInfo Info, TypeSymbol Type)> analyzedNullabilityMap, SnapshotManager? snapshotManager)
+            private DebugVerifier(ImmutableDictionary<BoundExpression, (NullabilityInfo Info, TypeSymbol? Type)> analyzedNullabilityMap, SnapshotManager? snapshotManager)
             {
                 _analyzedNullabilityMap = analyzedNullabilityMap;
                 _snapshotManager = snapshotManager;
@@ -34,7 +34,7 @@ protected override bool ConvertInsufficientExecutionStackExceptionToCancelledByS
                 return false; // Same behavior as NullableWalker
             }
 
-            public static void Verify(ImmutableDictionary<BoundExpression, (NullabilityInfo Info, TypeSymbol Type)> analyzedNullabilityMap, SnapshotManager? snapshotManagerOpt, BoundNode node)
+            public static void Verify(ImmutableDictionary<BoundExpression, (NullabilityInfo Info, TypeSymbol? Type)> analyzedNullabilityMap, SnapshotManager? snapshotManagerOpt, BoundNode node)
             {
                 var verifier = new DebugVerifier(analyzedNullabilityMap, snapshotManagerOpt);
                 verifier.Visit(node);

src/Compilers/CSharp/Portable/FlowAnalysis/NullableWalker.SnapshotManager.cs

@@ -55,7 +55,7 @@ private SnapshotManager(ImmutableArray<SharedWalkerState> walkerSharedStates, Im
                 int position,
                 BoundNode nodeToAnalyze,
                 Binder binder,
-                ImmutableDictionary<BoundExpression, (NullabilityInfo, TypeSymbol)>.Builder analyzedNullabilityMap,
+                ImmutableDictionary<BoundExpression, (NullabilityInfo, TypeSymbol?)>.Builder analyzedNullabilityMap,
                 SnapshotManager.Builder newManagerOpt)
             {
                 Snapshot incrementalSnapshot = GetSnapshotForPosition(position);
@@ -225,7 +225,7 @@ internal void ExitWalker(SharedWalkerState stableState, int previousSlot)
                     _currentWalkerSlot = previousSlot;
                 }
 
-                internal void TakeIncrementalSnapshot(BoundNode node, LocalState currentState)
+                internal void TakeIncrementalSnapshot(BoundNode? node, LocalState currentState)
                 {
                     if (node == null || node.WasCompilerGenerated)
                     {