Current proposal update.

src/Compilers/Core/Portable/Compilation/Extensions.cs

@@ -24,6 +24,12 @@ public static class ModelExtensions
             return semanticModel.GetSymbolInfo(node, cancellationToken);
         }
 
+        // If there is no single symbol, return will be the same as GetSymbolInfoWithNullability
+        public static SymbolInfo GetSymbolInfoWithNullability(this SemanticModel semanticModel, SyntaxNode, CancellationToken ct = default)
+        {
+            throw new NotImplementedException();
+        }
+
         /// <summary>
         /// Binds the node in the context of the specified location and get semantic information
         /// such as type, symbols and diagnostics. This method is used to get semantic information
@@ -60,6 +66,11 @@ public static SymbolInfo GetSpeculativeSymbolInfo(this SemanticModel semanticMod
             return semanticModel.GetTypeInfo(node, cancellationToken);
         }
 
+        public static TypeInfo GetTypeInfoWithNullability(this SemanticModel semanticModel, SyntaxNode node, CancellationToken cancellationToken = default)
+        {
+            throw new NotImplementedException();
+        }
+
         /// <summary>
         /// If "nameSyntax" resolves to an alias name, return the IAliasSymbol corresponding
         /// to A. Otherwise return null.
@@ -135,6 +146,46 @@ public static TypeInfo GetSpeculativeTypeInfo(this SemanticModel semanticModel,
             return semanticModel.GetDeclaredSymbolForNode(declaration, cancellationToken);
         }
 
+        public static TypeInfo GetTypeWithNullability(this SemanticModel semanticModel, IDiscardSymbol discard, CancellationToken ct = default)
+        {
+            throw new NotImplementedException();
+        }
+
+        public static TypeInfo GetTypeWithNullability(this SemanticModel semanticModel, IEventSymbol eventSymbol, CancellationToken ct = default)
+        {
+            throw new NotImplementedException();
+        }
+
+        public static TypeInfo GetTypeWithNullability(this SemanticModel semanticModel, IFieldSymbol field, CancellationToken ct = default)
+        {
+            throw new NotImplementedException();
+        }
+
+        public static TypeInfo GetTypeWithNullability(this SemanticModel semanticModel, ILocalSymbol local, CancellationToken ct = default)
+        {
+            throw new NotImplementedException();
+        }
+
+        public static TypeInfo GetReturnTypeWithNullability(this SemanticModel semanticModel, IMethodSymbol method, CancellationToken ct = default)
+        {
+            throw new NotImplementedException();
+        }
+
+        public static ImmutableArray<TypeInfo> GetTypeParametersWithNullability(this SemanticModel semanticModel, IMethodSymbol method, CancellationToken ct = default)
+        {
+            throw new NotImplementedException();
+        }
+
+        public static TypeInfo GetReceiverTypeWithNullability(this SemanticModel semanticModel, IMethodSymbol method, CancellationToken ct = default)
+        {
+            throw new NotImplementedException();
+        }
+
+        public static TypeInfo GetTypeWithNullability(this SemanticModel semanticModel, IParameterSymbol local, CancellationToken ct = default)
+        {
+            throw new NotImplementedException();
+        }
+
         /// <summary>
         /// Gets a list of method or indexed property symbols for a syntax node.
         /// </summary>

src/Compilers/Core/Portable/Compilation/TypeInfo.cs

@@ -35,11 +35,13 @@ public struct TypeInfo : IEquatable<TypeInfo>
         /// </summary>
         public Nullability ConvertedNullability { get; }
 
-        internal TypeInfo(ITypeSymbol type, ITypeSymbol convertedType)
+        internal TypeInfo(ITypeSymbol type, ITypeSymbol convertedType, Nullability nullability = Nullability.NotComputed, Nullability convertedNullability = Nullability.NotComputed)
             : this()
         {
             this.Type = type;
             this.ConvertedType = convertedType;
+            this.Nullability = nullability;
+            this.ConvertedNullability = convertedNullability;
         }
 
         public bool Equals(TypeInfo other)

src/Compilers/Core/Portable/PublicAPI.Unshipped.txt

@@ -30,11 +30,17 @@ Microsoft.CodeAnalysis.ISymbol.ToDisplayString(Microsoft.CodeAnalysis.Nullabilit
 Microsoft.CodeAnalysis.ISymbol.ToMinimalDisplayParts(Microsoft.CodeAnalysis.SemanticModel semanticModel, int position, Microsoft.CodeAnalysis.Nullability nullability, Microsoft.CodeAnalysis.SymbolDisplayFormat format = null) -> System.Collections.Immutable.ImmutableArray<Microsoft.CodeAnalysis.SymbolDisplayPart>
 Microsoft.CodeAnalysis.ISymbol.ToMinimalDisplayString(Microsoft.CodeAnalysis.SemanticModel semanticModel, int position, Microsoft.CodeAnalysis.Nullability nullability, Microsoft.CodeAnalysis.SymbolDisplayFormat format = null) -> string
 Microsoft.CodeAnalysis.ITypeParameterSymbol.ConstraintsNullability.get -> System.Collections.Immutable.ImmutableArray<Microsoft.CodeAnalysis.Nullability>
+Microsoft.CodeAnalysis.ITypeParameterSymbol.ReferenceTypeConstraintNullability.get -> Microsoft.CodeAnalysis.Nullability
+Microsoft.CodeAnalysis.ITypeSymbol.ToDisplayParts(Microsoft.CodeAnalysis.Nullability nullability, Microsoft.CodeAnalysis.SymbolDisplayFormat format = null) -> System.Collections.Immutable.ImmutableArray<Microsoft.CodeAnalysis.SymbolDisplayPart>
+Microsoft.CodeAnalysis.ITypeSymbol.ToDisplayString(Microsoft.CodeAnalysis.Nullability nullability, Microsoft.CodeAnalysis.SymbolDisplayFormat format = null) -> string
+Microsoft.CodeAnalysis.ITypeSymbol.ToMinimalDisplayParts(Microsoft.CodeAnalysis.SemanticModel semanticModel, int position, Microsoft.CodeAnalysis.Nullability nullability, Microsoft.CodeAnalysis.SymbolDisplayFormat format = null) -> System.Collections.Immutable.ImmutableArray<Microsoft.CodeAnalysis.SymbolDisplayPart>
+Microsoft.CodeAnalysis.ITypeSymbol.ToMinimalDisplayString(Microsoft.CodeAnalysis.SemanticModel semanticModel, int position, Microsoft.CodeAnalysis.Nullability nullability, Microsoft.CodeAnalysis.SymbolDisplayFormat format = null) -> string
 Microsoft.CodeAnalysis.Nullability
-Microsoft.CodeAnalysis.Nullability.MaybeNull = 3 -> Microsoft.CodeAnalysis.Nullability
-Microsoft.CodeAnalysis.Nullability.NonNull = 2 -> Microsoft.CodeAnalysis.Nullability
+Microsoft.CodeAnalysis.Nullability.MaybeNull = 4 -> Microsoft.CodeAnalysis.Nullability
+Microsoft.CodeAnalysis.Nullability.NonNull = 3 -> Microsoft.CodeAnalysis.Nullability
 Microsoft.CodeAnalysis.Nullability.NotApplicable = 0 -> Microsoft.CodeAnalysis.Nullability
-Microsoft.CodeAnalysis.Nullability.Unknown = 1 -> Microsoft.CodeAnalysis.Nullability
+Microsoft.CodeAnalysis.Nullability.NotComputed = 1 -> Microsoft.CodeAnalysis.Nullability
+Microsoft.CodeAnalysis.Nullability.Unknown = 2 -> Microsoft.CodeAnalysis.Nullability
 Microsoft.CodeAnalysis.OperationKind.SuppressNullableWarning = 97 -> Microsoft.CodeAnalysis.OperationKind
 Microsoft.CodeAnalysis.Operations.CommonConversion.IsImplicit.get -> bool
 Microsoft.CodeAnalysis.Operations.ISuppressNullableWarningOperation
@@ -150,6 +156,13 @@ static Microsoft.CodeAnalysis.FlowAnalysis.ControlFlowGraph.Create(Microsoft.Cod
 static Microsoft.CodeAnalysis.FlowAnalysis.ControlFlowGraph.Create(Microsoft.CodeAnalysis.Operations.IParameterInitializerOperation initializer, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) -> Microsoft.CodeAnalysis.FlowAnalysis.ControlFlowGraph
 static Microsoft.CodeAnalysis.FlowAnalysis.ControlFlowGraph.Create(Microsoft.CodeAnalysis.Operations.IPropertyInitializerOperation initializer, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) -> Microsoft.CodeAnalysis.FlowAnalysis.ControlFlowGraph
 static Microsoft.CodeAnalysis.FlowAnalysis.ControlFlowGraph.Create(Microsoft.CodeAnalysis.SyntaxNode node, Microsoft.CodeAnalysis.SemanticModel semanticModel, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) -> Microsoft.CodeAnalysis.FlowAnalysis.ControlFlowGraph
+static Microsoft.CodeAnalysis.ModelExtensions.GetReturnTypeWithNullability(this Microsoft.CodeAnalysis.SemanticModel semanticModel, Microsoft.CodeAnalysis.IMethodSymbol method, System.Threading.CancellationToken ct = default(System.Threading.CancellationToken)) -> Microsoft.CodeAnalysis.TypeInfo
+static Microsoft.CodeAnalysis.ModelExtensions.GetSymbolInfoWithNullability(this Microsoft.CodeAnalysis.SemanticModel semanticModel, Microsoft.CodeAnalysis.SyntaxNode , System.Threading.CancellationToken ct = default(System.Threading.CancellationToken)) -> Microsoft.CodeAnalysis.SymbolInfo
+static Microsoft.CodeAnalysis.ModelExtensions.GetTypeInfoWithNullability(this Microsoft.CodeAnalysis.SemanticModel semanticModel, Microsoft.CodeAnalysis.SyntaxNode node, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) -> Microsoft.CodeAnalysis.TypeInfo
+static Microsoft.CodeAnalysis.ModelExtensions.GetTypeWithNullability(this Microsoft.CodeAnalysis.SemanticModel semanticModel, Microsoft.CodeAnalysis.IEventSymbol eventSymbol, System.Threading.CancellationToken ct = default(System.Threading.CancellationToken)) -> Microsoft.CodeAnalysis.TypeInfo
+static Microsoft.CodeAnalysis.ModelExtensions.GetTypeWithNullability(this Microsoft.CodeAnalysis.SemanticModel semanticModel, Microsoft.CodeAnalysis.IFieldSymbol field, System.Threading.CancellationToken ct = default(System.Threading.CancellationToken)) -> Microsoft.CodeAnalysis.TypeInfo
+static Microsoft.CodeAnalysis.ModelExtensions.GetTypeWithNullability(this Microsoft.CodeAnalysis.SemanticModel semanticModel, Microsoft.CodeAnalysis.ILocalSymbol local, System.Threading.CancellationToken ct = default(System.Threading.CancellationToken)) -> Microsoft.CodeAnalysis.TypeInfo
+static Microsoft.CodeAnalysis.ModelExtensions.GetTypeWithNullability(this Microsoft.CodeAnalysis.SemanticModel semanticModel, Microsoft.CodeAnalysis.IParameterSymbol local, System.Threading.CancellationToken ct = default(System.Threading.CancellationToken)) -> Microsoft.CodeAnalysis.TypeInfo
 virtual Microsoft.CodeAnalysis.Operations.OperationVisitor.VisitCaughtException(Microsoft.CodeAnalysis.FlowAnalysis.ICaughtExceptionOperation operation) -> void
 virtual Microsoft.CodeAnalysis.Operations.OperationVisitor.VisitFlowCapture(Microsoft.CodeAnalysis.FlowAnalysis.IFlowCaptureOperation operation) -> void
 virtual Microsoft.CodeAnalysis.Operations.OperationVisitor.VisitFlowCaptureReference(Microsoft.CodeAnalysis.FlowAnalysis.IFlowCaptureReferenceOperation operation) -> void

src/Compilers/Core/Portable/Symbols/IDiscardSymbol.cs

@@ -14,10 +14,5 @@ public interface IDiscardSymbol : ISymbol
         /// The type of the discarded value.
         /// </summary>
         ITypeSymbol Type { get; }
-
-        /// <summary>
-        /// The nullability of the discarded value.
-        /// </summary>
-        Nullability Nullability { get; }
     }
 }

src/Compilers/Core/Portable/Symbols/IEventSymbol.cs

@@ -19,11 +19,6 @@ public interface IEventSymbol : ISymbol
         /// </summary>
         ITypeSymbol Type { get; }
 
-        /// <summary>
-        /// The declareted nullability of the this event.
-        /// </summary>
-        Nullability DeclaredNullability { get; }
-
         /// <summary>
         /// Returns true if the event is a WinRT type event.
         /// </summary>

src/Compilers/Core/Portable/Symbols/IFieldSymbol.cs

@@ -44,11 +44,6 @@ public interface IFieldSymbol : ISymbol
         /// </summary>
         ITypeSymbol Type { get; }
 
-        /// <summary>
-        /// The declared nullability of this field.
-        /// </summary>
-        Nullability DeclaredNullability { get; }
-
         /// <summary>
         /// Returns false if the field wasn't declared as "const", or constant value was omitted or erroneous.
         /// True otherwise.

src/Compilers/Core/Portable/Symbols/ILocalSymbol.cs

@@ -16,12 +16,6 @@ public interface ILocalSymbol : ISymbol
         /// </summary>
         ITypeSymbol Type { get; }
 
-        /// <summary>
-        /// The declared nullability of this local. If the local's type was inferred (i.e. via <code>var</code>), then
-        /// this declared nullability is inferred from the expression that initialized the local.
-        /// </summary>
-        Nullability DeclaredNullability { get; }
-
         /// <summary>
         /// Returns true if this local variable was declared as "const" (i.e. is a constant declaration).
         /// Also returns true for an enum member.

src/Compilers/Core/Portable/Symbols/IMethodSymbol.cs

@@ -90,24 +90,13 @@ public interface IMethodSymbol : ISymbol
         /// </summary>
         ITypeSymbol ReturnType { get; }
 
-        /// <summary>
-        /// Gets the declared nullability of the return type of the method.
-        /// </summary>
-        Nullability ReturnNullability { get; }
-
         /// <summary>
         /// Returns the type arguments that have been substituted for the type parameters. 
         /// If nothing has been substituted for a given type parameter,
         /// then the type parameter itself is consider the type argument.
         /// </summary>
         ImmutableArray<ITypeSymbol> TypeArguments { get; }
 
-        /// <summary>
-        /// Returns the nullability of the type arguments that have been substituted for the
-        /// type paramters.
-        /// </summary>
-        ImmutableArray<Nullability> TypeArgumentsNullability { get; }
-
         /// <summary>
         /// Get the type parameters on this method. If the method has not generic,
         /// returns an empty list.

src/Compilers/Core/Portable/Symbols/IParameterSymbol.cs

@@ -40,11 +40,6 @@ public interface IParameterSymbol : ISymbol
         /// </summary>
         ITypeSymbol Type { get; }
 
-        /// <summary>
-        /// Gets the declared nullability of the parameter
-        /// </summary>
-        Nullability DeclaredNullability { get; }
-
         /// <summary>
         /// Custom modifiers associated with the parameter type, or an empty array if there are none.
         /// </summary>

src/Compilers/Core/Portable/Symbols/IPropertySymbol.cs

@@ -55,11 +55,6 @@ public interface IPropertySymbol : ISymbol
         /// </summary>
         ITypeSymbol Type { get; }
 
-        /// <summary>
-        /// Gets the declared nullability of the property
-        /// </summary>
-        Nullability DeclaredNullability { get; }
-
         /// <summary>
         /// The parameters of this property. If this property has no parameters, returns
         /// an empty list. Parameters are only present on indexers, or on some properties

src/Compilers/Core/Portable/Symbols/ISymbol.cs

@@ -213,14 +213,6 @@ public interface ISymbol : IEquatable<ISymbol>
         /// <returns>A formatted string representation of the symbol.</returns>
         string ToDisplayString(SymbolDisplayFormat format = null);
 
-        /// <summary>
-        /// Converts the symbol to a string representation with given nullability.
-        /// </summary>
-        /// <param name="nullability">The nullability to use for the symbol.</param>
-        /// <param name="format">Format or null for the default.</param>
-        /// <returns>A formatted string representation of the symbol.</returns>
-        string ToDisplayString(Nullability nullability, SymbolDisplayFormat format = null);
-
         /// <summary>
         /// Convert a symbol to an array of string parts, each of which has a kind. Useful for
         /// colorizing the display string.
@@ -230,16 +222,6 @@ public interface ISymbol : IEquatable<ISymbol>
         /// <returns>A read-only array of string parts.</returns>
         ImmutableArray<SymbolDisplayPart> ToDisplayParts(SymbolDisplayFormat format = null);
 
-        /// <summary>
-        /// Convert a symbol to an array of string parts, each of which has a kind, with a given
-        /// nullability. Useful for colorizing the display string.
-        /// </summary>
-        /// <param name="nullability">The nullability to use for formatting.</param>
-        /// <param name="format">Formatting rules - null implies
-        /// SymbolDisplayFormat.ErrorMessageFormat.</param>
-        /// <returns>A read-only array of string parts.</returns>
-        ImmutableArray<SymbolDisplayPart> ToDisplayParts(Nullability nullability, SymbolDisplayFormat format = null);
-
         /// <summary>
         /// Convert a symbol to a string that can be displayed to the user. May be tailored to a
         /// specific location in the source code.
@@ -255,22 +237,6 @@ string ToMinimalDisplayString(
             int position,
             SymbolDisplayFormat format = null);
 
-        /// <summary>
-        /// Convert a symbol to a string that can be displayed to the user. May be tailored to a
-        /// specific location in the source code.
-        /// </summary>
-        /// <param name="semanticModel">Binding information (for determining names appropriate to
-        /// the context).</param>
-        /// <param name="position">A position in the source code (context).</param>
-        /// <param name="nullability">The nullability to use in formatting.</param>
-        /// <param name="format">Formatting rules - null implies
-        /// <returns>A formatted string that can be displayed to the user.</returns>
-        string ToMinimalDisplayString(
-            SemanticModel semanticModel,
-            int position,
-            Nullability nullability,
-            SymbolDisplayFormat format = null);
-
         /// <summary>
         /// Convert a symbol to an array of string parts, each of which has a kind. May be tailored
         /// to a specific location in the source code. Useful for colorizing the display string.
@@ -286,24 +252,6 @@ ImmutableArray<SymbolDisplayPart> ToMinimalDisplayParts(
             int position,
             SymbolDisplayFormat format = null);
 
-        /// <summary>
-        /// Convert a symbol to an array of string parts, each of which has a kind, including
-        /// nullability. May be tailored to a specific location in the source code. Useful 
-        /// for colorizing the display string.
-        /// </summary>
-        /// <param name="semanticModel">Binding information (for determining names appropriate to
-        /// the context).</param>
-        /// <param name="position">A position in the source code (context).</param>
-        /// <param name="nullability">The nullability to use in formatting.</param>
-        /// <param name="format">Formatting rules - null implies
-        /// SymbolDisplayFormat.MinimallyQualifiedFormat.</param>
-        /// <returns>A read-only array of string parts.</returns>
-        ImmutableArray<SymbolDisplayPart> ToMinimalDisplayParts(
-            SemanticModel semanticModel,
-            int position,
-            Nullability nullability,
-            SymbolDisplayFormat format = null);
-
         /// <summary>
         /// Indicates that this symbol uses metadata that cannot be supported by the language.
         /// 

src/Compilers/Core/Portable/Symbols/ITypeParameterSymbol.cs

@@ -45,6 +45,11 @@ public interface ITypeParameterSymbol : ITypeSymbol
         /// </summary>
         bool HasReferenceTypeConstraint { get; }
 
+        /// <summary>
+        /// <see cref="Nullability.NotApplicable"/> if <see cref="HasReferenceTypeConstraint"/> is false.
+        /// </summary>
+        Nullability ReferenceTypeConstraintNullability { get; }
+
         /// <summary>
         /// True if the value type constraint (<c>struct</c>) was specified for the type parameter.
         /// </summary>