Annotate more of the binder

src/Compilers/CSharp/Portable/Binder/Binder.cs

@@ -674,7 +674,7 @@ internal static ObsoleteDiagnosticKind ReportDiagnosticsIfObsoleteInternal(Diagn
         internal static bool IsSymbolAccessibleConditional(
             Symbol symbol,
             AssemblySymbol within,
-            ref HashSet<DiagnosticInfo> useSiteDiagnostics)
+            ref HashSet<DiagnosticInfo>? useSiteDiagnostics)
         {
             return AccessCheck.IsSymbolAccessible(symbol, within, ref useSiteDiagnostics);
         }
@@ -682,7 +682,7 @@ internal static ObsoleteDiagnosticKind ReportDiagnosticsIfObsoleteInternal(Diagn
         internal bool IsSymbolAccessibleConditional(
             Symbol symbol,
             NamedTypeSymbol within,
-            ref HashSet<DiagnosticInfo> useSiteDiagnostics,
+            ref HashSet<DiagnosticInfo>? useSiteDiagnostics,
             TypeSymbol? throughTypeOpt = null)
         {
             return this.Flags.Includes(BinderFlags.IgnoreAccessibility) || AccessCheck.IsSymbolAccessible(symbol, within, ref useSiteDiagnostics, throughTypeOpt);
@@ -693,7 +693,7 @@ internal static ObsoleteDiagnosticKind ReportDiagnosticsIfObsoleteInternal(Diagn
             NamedTypeSymbol within,
             TypeSymbol throughTypeOpt,
             out bool failedThroughTypeCheck,
-            ref HashSet<DiagnosticInfo> useSiteDiagnostics,
+            ref HashSet<DiagnosticInfo>? useSiteDiagnostics,
             ConsList<TypeSymbol>? basesBeingResolved = null)
         {
             if (this.Flags.Includes(BinderFlags.IgnoreAccessibility))

src/Compilers/CSharp/Portable/Binder/Binder_AnonymousTypes.cs

-// Licensed to the .NET Foundation under one or more agreements.
+// Licensed to the .NET Foundation under one or more agreements.
 // 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.Collections.Generic;
 using System.Diagnostics;
@@ -8,6 +9,7 @@
 using Microsoft.CodeAnalysis.CSharp.Symbols;
 using Microsoft.CodeAnalysis.CSharp.Syntax;
 using Microsoft.CodeAnalysis.PooledObjects;
+using Roslyn.Utilities;
 
 namespace Microsoft.CodeAnalysis.CSharp
 {
@@ -40,7 +42,7 @@ private BoundExpression BindAnonymousObjectCreation(AnonymousObjectCreationExpre
             for (int i = 0; i < fieldCount; i++)
             {
                 AnonymousObjectMemberDeclaratorSyntax fieldInitializer = initializers[i];
-                NameEqualsSyntax nameEquals = fieldInitializer.NameEquals;
+                NameEqualsSyntax? nameEquals = fieldInitializer.NameEquals;
                 ExpressionSyntax expression = fieldInitializer.Expression;
 
                 SyntaxToken nameToken = default(SyntaxToken);
@@ -63,11 +65,11 @@ private BoundExpression BindAnonymousObjectCreation(AnonymousObjectCreationExpre
                 boundExpressions[i] = BindRValueWithoutTargetType(expression, diagnostics);
 
                 //  check the name to be unique
-                string fieldName = null;
+                string? fieldName = null;
                 if (nameToken.Kind() == SyntaxKind.IdentifierToken)
                 {
                     fieldName = nameToken.ValueText;
-                    if (!uniqueFieldNames.Add(fieldName))
+                    if (!uniqueFieldNames.Add(fieldName!))
                     {
                         //  name duplication
                         Error(diagnostics, ErrorCode.ERR_AnonymousTypeDuplicatePropertyName, fieldInitializer);
@@ -85,7 +87,7 @@ private BoundExpression BindAnonymousObjectCreation(AnonymousObjectCreationExpre
                 TypeSymbol fieldType = GetAnonymousTypeFieldType(boundExpressions[i], fieldInitializer, diagnostics, ref hasError);
 
                 // build anonymous type field descriptor
-                fieldSyntaxNodes[i] = (nameToken.Kind() == SyntaxKind.IdentifierToken) ? (CSharpSyntaxNode)nameToken.Parent : fieldInitializer;
+                fieldSyntaxNodes[i] = (nameToken.Kind() == SyntaxKind.IdentifierToken) ? (CSharpSyntaxNode)nameToken.Parent! : fieldInitializer;
                 fields[i] = new AnonymousTypeField(
                     fieldName == null ? "$" + i.ToString() : fieldName,
                     fieldSyntaxNodes[i].Location,
@@ -107,7 +109,7 @@ private BoundExpression BindAnonymousObjectCreation(AnonymousObjectCreationExpre
                 ArrayBuilder<BoundAnonymousPropertyDeclaration>.GetInstance();
             for (int i = 0; i < fieldCount; i++)
             {
-                NameEqualsSyntax explicitName = initializers[i].NameEquals;
+                NameEqualsSyntax? explicitName = initializers[i].NameEquals;
                 if (explicitName != null)
                 {
                     AnonymousTypeField field = fields[i];
@@ -178,7 +180,7 @@ private static bool IsAnonymousTypeMemberExpression(ExpressionSyntax expr)
         private bool IsAnonymousTypesAllowed()
         {
             var member = this.ContainingMemberOrLambda;
-            if ((object)member == null)
+            if (member is null)
             {
                 return false;
             }
@@ -205,13 +207,14 @@ private bool IsAnonymousTypesAllowed()
         /// </summary>
         private TypeSymbol GetAnonymousTypeFieldType(BoundExpression expression, CSharpSyntaxNode errorSyntax, DiagnosticBag diagnostics, ref bool hasError)
         {
-            object errorArg = null;
-            TypeSymbol expressionType = expression.Type;
+            object? errorArg = null;
+            TypeSymbol? expressionType = expression.Type;
 
             if (!expression.HasAnyErrors)
             {
                 if (expression.HasExpressionType())
                 {
+                    RoslynDebug.Assert(expressionType is object);
                     if (expressionType.IsVoidType())
                     {
                         errorArg = expressionType;
@@ -233,7 +236,7 @@ private TypeSymbol GetAnonymousTypeFieldType(BoundExpression expression, CSharpS
                 }
             }
 
-            if ((object)expressionType == null)
+            if (expressionType is null)
             {
                 expressionType = CreateErrorType("error");
             }

src/Compilers/CSharp/Portable/Binder/Binder_Await.cs

-// Licensed to the .NET Foundation under one or more agreements.
+// Licensed to the .NET Foundation under one or more agreements.
 // 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.Collections.Generic;
 using System.Collections.Immutable;
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 using Microsoft.CodeAnalysis.CSharp.Symbols;
 using Microsoft.CodeAnalysis.CSharp.Syntax;
+using Roslyn.Utilities;
 
 namespace Microsoft.CodeAnalysis.CSharp
 {
@@ -45,15 +48,15 @@ internal void ReportBadAwaitDiagnostics(SyntaxNode node, Location location, Diag
             hasErrors |= ReportBadAwaitContext(node, location, diagnostics);
         }
 
-        internal BoundAwaitableInfo BindAwaitInfo(BoundAwaitableValuePlaceholder placeholder, SyntaxNode node, DiagnosticBag diagnostics, ref bool hasErrors, BoundExpression expressionOpt = null)
+        internal BoundAwaitableInfo BindAwaitInfo(BoundAwaitableValuePlaceholder placeholder, SyntaxNode node, DiagnosticBag diagnostics, ref bool hasErrors, BoundExpression? expressionOpt = null)
         {
             bool hasGetAwaitableErrors = !GetAwaitableExpressionInfo(
                 expressionOpt ?? placeholder,
                 placeholder,
                 out bool isDynamic,
-                out BoundExpression getAwaiter,
-                out PropertySymbol isCompleted,
-                out MethodSymbol getResult,
+                out BoundExpression? getAwaiter,
+                out PropertySymbol? isCompleted,
+                out MethodSymbol? getResult,
                 getAwaiterGetResultCall: out _,
                 node,
                 diagnostics);
@@ -78,7 +81,7 @@ private bool CouldBeAwaited(BoundExpression expression)
             }
 
             var type = expression.Type;
-            if (((object)type == null) ||
+            if ((type is null) ||
                 type.IsDynamic() ||
                 (type.IsVoidType()))
             {
@@ -101,7 +104,7 @@ private bool CouldBeAwaited(BoundExpression expression)
 
             // Finally, if we're in an async method, and the expression could be awaited, report that it is instead discarded.
             var containingMethod = this.ContainingMemberOrLambda as MethodSymbol;
-            if ((object)containingMethod == null || !containingMethod.IsAsync)
+            if (containingMethod is null || !containingMethod.IsAsync)
             {
                 return false;
             }
@@ -136,9 +139,9 @@ private bool ContextForbidsAwait
         /// <returns>True if the expression contains errors.</returns>
         private bool ReportBadAwaitWithoutAsync(Location location, DiagnosticBag diagnostics)
         {
-            DiagnosticInfo info = null;
+            DiagnosticInfo? info = null;
             var containingMemberOrLambda = this.ContainingMemberOrLambda;
-            if ((object)containingMemberOrLambda != null)
+            if (containingMemberOrLambda is object)
             {
                 switch (containingMemberOrLambda.Kind)
                 {
@@ -230,7 +233,7 @@ private bool ReportBadAwaitContext(SyntaxNode node, Location location, Diagnosti
         /// <returns>True if the expression is awaitable; false otherwise.</returns>
         internal bool GetAwaitableExpressionInfo(
             BoundExpression expression,
-            out BoundExpression getAwaiterGetResultCall,
+            [NotNullWhen(true)] out BoundExpression? getAwaiterGetResultCall,
             SyntaxNode node,
             DiagnosticBag diagnostics)
         {
@@ -241,10 +244,10 @@ private bool ReportBadAwaitContext(SyntaxNode node, Location location, Diagnosti
             BoundExpression expression,
             BoundExpression getAwaiterArgument,
             out bool isDynamic,
-            out BoundExpression getAwaiter,
-            out PropertySymbol isCompleted,
-            out MethodSymbol getResult,
-            out BoundExpression getAwaiterGetResultCall,
+            out BoundExpression? getAwaiter,
+            out PropertySymbol? isCompleted,
+            out MethodSymbol? getResult,
+            out BoundExpression? getAwaiterGetResultCall,
             SyntaxNode node,
             DiagnosticBag diagnostics)
         {
@@ -272,10 +275,10 @@ private bool ReportBadAwaitContext(SyntaxNode node, Location location, Diagnosti
                 return false;
             }
 
-            TypeSymbol awaiterType = getAwaiter.Type;
-            return GetIsCompletedProperty(awaiterType, node, expression.Type, diagnostics, out isCompleted)
+            TypeSymbol awaiterType = getAwaiter.Type!;
+            return GetIsCompletedProperty(awaiterType, node, expression.Type!, diagnostics, out isCompleted)
                 && AwaiterImplementsINotifyCompletion(awaiterType, node, diagnostics)
-                && GetGetResultMethod(getAwaiter, node, expression.Type, diagnostics, out getResult, out getAwaiterGetResultCall);
+                && GetGetResultMethod(getAwaiter, node, expression.Type!, diagnostics, out getResult, out getAwaiterGetResultCall);
         }
 
         /// <summary>
@@ -289,7 +292,7 @@ private static bool ValidateAwaitedExpression(BoundExpression expression, Syntax
                 return false;
             }
 
-            if ((object)expression.Type == null)
+            if (expression.Type is null)
             {
                 Error(diagnostics, ErrorCode.ERR_BadAwaitArgIntrinsic, node, expression.Display);
                 return false;
@@ -309,8 +312,9 @@ private static bool ValidateAwaitedExpression(BoundExpression expression, Syntax
         /// NOTE: this is an error in the spec.  An extension method of the form
         /// Awaiter&lt;T&gt; GetAwaiter&lt;T&gt;(this Task&lt;T&gt;) may be used.
         /// </remarks>
-        private bool GetGetAwaiterMethod(BoundExpression expression, SyntaxNode node, DiagnosticBag diagnostics, out BoundExpression getAwaiterCall)
+        private bool GetGetAwaiterMethod(BoundExpression expression, SyntaxNode node, DiagnosticBag diagnostics, [NotNullWhen(true)] out BoundExpression? getAwaiterCall)
         {
+            RoslynDebug.Assert(expression.Type is object);
             if (expression.Type.IsVoidType())
             {
                 Error(diagnostics, ErrorCode.ERR_BadAwaitArgVoidCall, node);
@@ -352,7 +356,7 @@ private bool GetGetAwaiterMethod(BoundExpression expression, SyntaxNode node, Di
         /// Spec 7.7.7.1:
         /// An Awaiter A has an accessible, readable instance property IsCompleted of type bool.
         /// </remarks>
-        private bool GetIsCompletedProperty(TypeSymbol awaiterType, SyntaxNode node, TypeSymbol awaitedExpressionType, DiagnosticBag diagnostics, out PropertySymbol isCompletedProperty)
+        private bool GetIsCompletedProperty(TypeSymbol awaiterType, SyntaxNode node, TypeSymbol awaitedExpressionType, DiagnosticBag diagnostics, [NotNullWhen(true)] out PropertySymbol? isCompletedProperty)
         {
             var receiver = new BoundLiteral(node, ConstantValue.Null, awaiterType);
             var name = WellKnownMemberNames.IsCompleted;
@@ -398,7 +402,7 @@ private bool GetIsCompletedProperty(TypeSymbol awaiterType, SyntaxNode node, Typ
         private bool AwaiterImplementsINotifyCompletion(TypeSymbol awaiterType, SyntaxNode node, DiagnosticBag diagnostics)
         {
             var INotifyCompletion = GetWellKnownType(WellKnownType.System_Runtime_CompilerServices_INotifyCompletion, diagnostics, node);
-            HashSet<DiagnosticInfo> useSiteDiagnostics = null;
+            HashSet<DiagnosticInfo>? useSiteDiagnostics = null;
 
             var conversion = this.Conversions.ClassifyImplicitConversionFromType(awaiterType, INotifyCompletion, ref useSiteDiagnostics);
             if (!conversion.IsImplicit)
@@ -419,7 +423,7 @@ private bool AwaiterImplementsINotifyCompletion(TypeSymbol awaiterType, SyntaxNo
         /// Spec 7.7.7.1:
         /// An Awaiter A has an accessible instance method GetResult with no parameters and no type parameters.
         /// </remarks>
-        private bool GetGetResultMethod(BoundExpression awaiterExpression, SyntaxNode node, TypeSymbol awaitedExpressionType, DiagnosticBag diagnostics, out MethodSymbol getResultMethod, out BoundExpression getAwaiterGetResultCall)
+        private bool GetGetResultMethod(BoundExpression awaiterExpression, SyntaxNode node, TypeSymbol awaitedExpressionType, DiagnosticBag diagnostics, out MethodSymbol? getResultMethod, [NotNullWhen(true)] out BoundExpression? getAwaiterGetResultCall)
         {
             var awaiterType = awaiterExpression.Type;
             getAwaiterGetResultCall = MakeInvocationExpression(node, awaiterExpression, WellKnownMemberNames.GetResult, ImmutableArray<BoundExpression>.Empty, diagnostics);
@@ -430,6 +434,7 @@ private bool GetGetResultMethod(BoundExpression awaiterExpression, SyntaxNode no
                 return false;
             }
 
+            RoslynDebug.Assert(awaiterType is object);
             if (getAwaiterGetResultCall.Kind != BoundKind.Call)
             {
                 Error(diagnostics, ErrorCode.ERR_NoSuchMember, node, awaiterType, WellKnownMemberNames.GetResult);
@@ -461,7 +466,7 @@ private bool GetGetResultMethod(BoundExpression awaiterExpression, SyntaxNode no
 
         private static bool HasOptionalOrVariableParameters(MethodSymbol method)
         {
-            Debug.Assert(method != null);
+            RoslynDebug.Assert(method != null);
 
             if (method.ParameterCount != 0)
             {

src/Compilers/CSharp/Portable/Binder/Binder_Constraints.cs

-// Licensed to the .NET Foundation under one or more agreements.
+// Licensed to the .NET Foundation under one or more agreements.
 // 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.Collections.Generic;
 using System.Collections.Immutable;
@@ -30,7 +31,7 @@ internal partial class Binder
             bool isForOverride = false)
         {
             Debug.Assert(this.Flags.Includes(BinderFlags.GenericConstraintsClause));
-            Debug.Assert((object)containingSymbol != null);
+            RoslynDebug.Assert((object)containingSymbol != null);
             Debug.Assert((containingSymbol.Kind == SymbolKind.NamedType) || (containingSymbol.Kind == SymbolKind.Method));
             Debug.Assert(typeParameters.Length > 0);
             Debug.Assert(clauses.Count > 0);
@@ -51,20 +52,20 @@ internal partial class Binder
             }
 
             // An array of constraint clauses, one for each type parameter, indexed by ordinal.
-            var results = ArrayBuilder<TypeParameterConstraintClause>.GetInstance(n, fillWithValue: null);
-            var syntaxNodes = ArrayBuilder<ArrayBuilder<TypeConstraintSyntax>>.GetInstance(n, fillWithValue: null);
+            var results = ArrayBuilder<TypeParameterConstraintClause?>.GetInstance(n, fillWithValue: null);
+            var syntaxNodes = ArrayBuilder<ArrayBuilder<TypeConstraintSyntax>?>.GetInstance(n, fillWithValue: null);
 
             // Bind each clause and add to the results.
             foreach (var clause in clauses)
             {
                 var name = clause.Name.Identifier.ValueText;
                 int ordinal;
-                if (names.TryGetValue(name, out ordinal))
+                if (names.TryGetValue(name!, out ordinal))
                 {
                     Debug.Assert(ordinal >= 0);
                     Debug.Assert(ordinal < n);
 
-                    (TypeParameterConstraintClause constraintClause, ArrayBuilder<TypeConstraintSyntax> typeConstraintNodes) = this.BindTypeParameterConstraints(typeParameterList.Parameters[ordinal], clause, isForOverride, diagnostics);
+                    (TypeParameterConstraintClause constraintClause, ArrayBuilder<TypeConstraintSyntax>? typeConstraintNodes) = this.BindTypeParameterConstraints(typeParameterList.Parameters[ordinal], clause, isForOverride, diagnostics);
                     if (results[ordinal] == null)
                     {
                         results[ordinal] = constraintClause;
@@ -100,7 +101,7 @@ internal partial class Binder
 
             TypeParameterConstraintClause.AdjustConstraintTypes(containingSymbol, typeParameters, results, ref isValueTypeOverride);
 
-            RemoveInvalidConstraints(typeParameters, results, syntaxNodes, diagnostics);
+            RemoveInvalidConstraints(typeParameters, results!, syntaxNodes, diagnostics);
 
             foreach (var typeConstraintsSyntaxes in syntaxNodes)
             {
@@ -109,17 +110,17 @@ internal partial class Binder
 
             syntaxNodes.Free();
 
-            return results.ToImmutableAndFree();
+            return results.ToImmutableAndFree()!;
         }
 
         /// <summary>
         /// Bind and return a single type parameter constraint clause along with syntax nodes corresponding to type constraints.
         /// </summary>
-        private (TypeParameterConstraintClause, ArrayBuilder<TypeConstraintSyntax>) BindTypeParameterConstraints(TypeParameterSyntax typeParameterSyntax, TypeParameterConstraintClauseSyntax constraintClauseSyntax, bool isForOverride, DiagnosticBag diagnostics)
+        private (TypeParameterConstraintClause, ArrayBuilder<TypeConstraintSyntax>?) BindTypeParameterConstraints(TypeParameterSyntax typeParameterSyntax, TypeParameterConstraintClauseSyntax constraintClauseSyntax, bool isForOverride, DiagnosticBag diagnostics)
         {
             var constraints = TypeParameterConstraintKind.None;
-            ArrayBuilder<TypeWithAnnotations> constraintTypes = null;
-            ArrayBuilder<TypeConstraintSyntax> syntaxBuilder = null;
+            ArrayBuilder<TypeWithAnnotations>? constraintTypes = null;
+            ArrayBuilder<TypeConstraintSyntax>? syntaxBuilder = null;
             SeparatedSyntaxList<TypeParameterConstraintSyntax> constraintsSyntax = constraintClauseSyntax.Constraints;
             Debug.Assert(!InExecutableBinder); // Cannot eagerly report diagnostics handled by LazyMissingNonNullTypesContextDiagnosticInfo 
             bool hasTypeLikeConstraint = false;
@@ -258,7 +259,7 @@ internal partial class Binder
                             }
 
                             constraintTypes.Add(type);
-                            syntaxBuilder.Add(typeConstraintSyntax);
+                            syntaxBuilder!.Add(typeConstraintSyntax);
                         }
                         continue;
                     default:
@@ -309,7 +310,7 @@ private TypeParameterConstraintClause GetDefaultTypeParameterConstraintClause(Ty
         private static void RemoveInvalidConstraints(
             ImmutableArray<TypeParameterSymbol> typeParameters,
             ArrayBuilder<TypeParameterConstraintClause> constraintClauses,
-            ArrayBuilder<ArrayBuilder<TypeConstraintSyntax>> syntaxNodes,
+            ArrayBuilder<ArrayBuilder<TypeConstraintSyntax>?> syntaxNodes,
             DiagnosticBag diagnostics)
         {
             Debug.Assert(typeParameters.Length > 0);
@@ -324,7 +325,7 @@ private TypeParameterConstraintClause GetDefaultTypeParameterConstraintClause(Ty
         private static TypeParameterConstraintClause RemoveInvalidConstraints(
             TypeParameterSymbol typeParameter,
             TypeParameterConstraintClause constraintClause,
-            ArrayBuilder<TypeConstraintSyntax> syntaxNodesOpt,
+            ArrayBuilder<TypeConstraintSyntax>? syntaxNodesOpt,
             DiagnosticBag diagnostics)
         {
             if (syntaxNodesOpt != null)
@@ -367,7 +368,7 @@ private TypeParameterConstraintClause GetDefaultTypeParameterConstraintClause(Ty
             TypeWithAnnotations constraintType,
             DiagnosticBag diagnostics)
         {
-            HashSet<DiagnosticInfo> useSiteDiagnostics = null;
+            HashSet<DiagnosticInfo>? useSiteDiagnostics = null;
             if (!containingSymbol.IsNoMoreVisibleThan(constraintType, ref useSiteDiagnostics))
             {
                 // "Inconsistent accessibility: constraint type '{1}' is less accessible than '{0}'"

src/Compilers/CSharp/Portable/Binder/BuckStopsHereBinder.cs

@@ -60,7 +60,7 @@ internal override Imports GetImports(ConsList<TypeSymbol> basesBeingResolved)
 
         protected override bool InExecutableBinder => false;
 
-        internal override bool IsAccessibleHelper(Symbol symbol, TypeSymbol accessThroughType, out bool failedThroughTypeCheck, ref HashSet<DiagnosticInfo> useSiteDiagnostics, ConsList<TypeSymbol> basesBeingResolved)
+        internal override bool IsAccessibleHelper(Symbol symbol, TypeSymbol accessThroughType, out bool failedThroughTypeCheck, ref HashSet<DiagnosticInfo>? useSiteDiagnostics, ConsList<TypeSymbol> basesBeingResolved)
         {
             failedThroughTypeCheck = false;
             return IsSymbolAccessibleConditional(symbol, Compilation.Assembly, ref useSiteDiagnostics);

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

@@ -1783,11 +1783,11 @@ internal bool ReturnsAwaitableToVoidOrInt(MethodSymbol method, DiagnosticBag dia
             var syntax = method.ExtractReturnTypeSyntax();
             var dumbInstance = new BoundLiteral(syntax, ConstantValue.Null, namedType);
             var binder = GetBinder(syntax);
-            BoundExpression result;
+            BoundExpression? result;
             var success = binder.GetAwaitableExpressionInfo(dumbInstance, out result, syntax, diagnostics);
 
             return success &&
-                (result.Type!.IsVoidType() || result.Type!.SpecialType == SpecialType.System_Int32);
+                (result!.Type!.IsVoidType() || result.Type!.SpecialType == SpecialType.System_Int32);
         }
 
         /// <summary>
@@ -3168,7 +3168,7 @@ protected override IPointerTypeSymbol CommonCreatePointerTypeSymbol(ITypeSymbol
             return NamedTypeSymbol.CreateTuple(
                 locationOpt: null, // no location for the type declaration
                 elementTypesWithAnnotations: typesBuilder.ToImmutableAndFree(),
-                elementLocations: elementLocations,
+                elementLocations: elementLocations!,
                 elementNames: elementNames,
                 compilation: this,
                 shouldCheckConstraints: false,
@@ -3194,7 +3194,7 @@ protected override IPointerTypeSymbol CommonCreatePointerTypeSymbol(ITypeSymbol
             CheckTupleElementNullableAnnotations(cardinality, elementNullableAnnotations);
 
             var tupleType = NamedTypeSymbol.CreateTuple(
-                csharpUnderlyingTuple, elementNames, elementLocations: elementLocations);
+                csharpUnderlyingTuple, elementNames, elementLocations: elementLocations!);
             if (!elementNullableAnnotations.IsDefault)
             {
                 tupleType = tupleType.WithElementTypes(

src/Compilers/CSharp/Portable/Symbols/SymbolExtensions.cs

@@ -91,7 +91,7 @@ public static bool IsNoMoreVisibleThan(this Symbol symbol, TypeSymbol type, ref
             return type.IsAtLeastAsVisibleAs(symbol, ref useSiteDiagnostics);
         }
 
-        public static bool IsNoMoreVisibleThan(this Symbol symbol, TypeWithAnnotations type, ref HashSet<DiagnosticInfo> useSiteDiagnostics)
+        public static bool IsNoMoreVisibleThan(this Symbol symbol, TypeWithAnnotations type, ref HashSet<DiagnosticInfo>? useSiteDiagnostics)
         {
             return type.IsAtLeastAsVisibleAs(symbol, ref useSiteDiagnostics);
         }

src/Compilers/CSharp/Portable/Symbols/Tuples/TupleTypeSymbol.cs

@@ -29,7 +29,7 @@ internal abstract partial class NamedTypeSymbol
         internal static NamedTypeSymbol CreateTuple(
             Location? locationOpt,
             ImmutableArray<TypeWithAnnotations> elementTypesWithAnnotations,
-            ImmutableArray<Location> elementLocations,
+            ImmutableArray<Location?> elementLocations,
             ImmutableArray<string?> elementNames,
             CSharpCompilation compilation,
             bool shouldCheckConstraints,
@@ -104,7 +104,7 @@ static NamedTypeSymbol getTupleUnderlyingType(ImmutableArray<TypeWithAnnotations
             NamedTypeSymbol tupleCompatibleType,
             ImmutableArray<string?> elementNames = default,
             ImmutableArray<bool> errorPositions = default,
-            ImmutableArray<Location> elementLocations = default,
+            ImmutableArray<Location?> elementLocations = default,
             ImmutableArray<Location> locations = default)
         {
             Debug.Assert(tupleCompatibleType.IsTupleType);
@@ -162,7 +162,7 @@ internal NamedTypeSymbol WithElementTypes(ImmutableArray<TypeWithAnnotations> ne
         /// Drops the inferred positions.
         /// </summary>
         internal NamedTypeSymbol WithElementNames(ImmutableArray<string?> newElementNames,
-                                                  ImmutableArray<Location> newElementLocations,
+                                                  ImmutableArray<Location?> newElementLocations,
                                                   ImmutableArray<bool> errorPositions,
                                                   ImmutableArray<Location> locations)
         {
@@ -555,7 +555,7 @@ public sealed override bool IsTupleType
         private ImmutableArray<bool> TupleErrorPositions
             => _lazyTupleData is null ? default : _lazyTupleData.ErrorPositions;
 
-        private ImmutableArray<Location> TupleElementLocations
+        private ImmutableArray<Location?> TupleElementLocations
             => _lazyTupleData is null ? default : _lazyTupleData.ElementLocations;
 
         public sealed override ImmutableArray<TypeWithAnnotations> TupleElementTypesWithAnnotations
@@ -898,7 +898,7 @@ internal sealed class TupleExtraData
             /// Declaration locations for individual elements, if provided.
             /// Declaration location for this tuple type symbol
             /// </summary>
-            internal ImmutableArray<Location> ElementLocations { get; }
+            internal ImmutableArray<Location?> ElementLocations { get; }
 
             /// <summary>
             /// Which element names were inferred and therefore cannot be used.
@@ -933,7 +933,7 @@ internal TupleExtraData(NamedTypeSymbol underlyingType)
             }
 
             internal TupleExtraData(NamedTypeSymbol underlyingType, ImmutableArray<string?> elementNames,
-                ImmutableArray<Location> elementLocations, ImmutableArray<bool> errorPositions, ImmutableArray<Location> locations)
+                ImmutableArray<Location?> elementLocations, ImmutableArray<bool> errorPositions, ImmutableArray<Location> locations)
                 : this(underlyingType)
             {
                 ElementNames = elementNames;

src/Compilers/CSharp/Portable/Symbols/TypeSymbolExtensions.cs

@@ -488,9 +488,9 @@ public static MethodSymbol DelegateInvokeMethod(this TypeSymbol type)
             return null;
         }
 
-        public static SpecialType GetSpecialTypeSafe(this TypeSymbol type)
+        public static SpecialType GetSpecialTypeSafe(this TypeSymbol? type)
         {
-            return (object)type != null ? type.SpecialType : SpecialType.None;
+            return type is object ? type.SpecialType : SpecialType.None;
         }
 
         public static bool IsAtLeastAsVisibleAs(this TypeSymbol type, Symbol sym, ref HashSet<DiagnosticInfo>? useSiteDiagnostics)